Cultivation
Cannabis originated in China with evidence tracing back to the Neolithic Age (10,000 BC).
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Since the agricultural revolution, humans have been adapting and altering practices for large-scale cultivation of this plant. Before state-by-state legalization, the underground growers of the 20th century developed some of the most groundbreaking feats in breeding, cultivation, curing, and of course distribution of this plant on a large scale for both indoor, outdoor, and greenhouse growth.
Academia is just beginning to catch up and learn about the techniques that have been long utilized in industry and the underground. Though academia has been able to provide quantitative tools to standardize and explain what is going on inside the plant.
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Here is some of what is known by each thus far:
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Frequently Asked Questions (FAQ):
Q: What is the difference between Cannabis Sativa and Indica?
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A: Taxonomically, Indica plants are broad-leafed, with short structures, and typically reach fruit or bud maturity earlier, modeled by plants from Afghanistan. In Contrast, Sativa plants typically have narrow leaves, are taller and less bushy than Indicas, and typically reach fruit or bud maturity later, modeled by plants from India.
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Chemically, one cannot distinguish between cannabinoid content or effect based on sativa or indica growth patterns. Classification of Sativas as more energetic or Indicas as calming is based on anecdotal reports not based on the plant's structure.
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Q: What is Ruderalis?
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A: These are wild-type plants not typically cultivated for commercial purposes. Their flowering cycles are not induced by light like cannabis sativa or indica. They also typically have equal CBD to THC content.
Q: What is the best method for irrigation?
A: Higher frequency watering with smaller volumes of growing substrate tends to be favored. Dry downs are still necessary for root expansion and to prevent root rot.
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Q: What is the best substrate to grow in?
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A: This depends on where you are growing and what nutrient amendments you are using. It is universally observed that well-aerated porous substrates produce optimal growth conditions.
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Q: What nutrients are required?
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A: Nutrient requirements can be placed into three major categories. Primary macronutrients, are utilized in high amounts and are prone to deficiency these are nitrogen, potassium, and phosphorus. Secondary macronutrients are utilized slightly less than primary macronutrients but are still used in high amounts. These are calcium, magnesium, and sulfur. Finally, micronutrients utilized in smaller amounts by the plant and though not prone to deficiency may still occur. These are iron, zinc, manganese, molybdenum, copper, and boron.
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Q: Why do environmental conditions such as light cycles, light requirements, temperature, and humidity change at different stages of growth (flower vs. veg)?
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A: For light cycles this changes to mimic the time of year with longer days typically observed at the beginning of the season in early summer when the plant is in the vegetative stage. The days are shorter towards the end of the summer when the plant begins to flower and prepare for harvest.
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Q: Why do some strains/cultivars grow taller?
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A: Varieties that originate closer to the equator typically mature later. This gives them more time during the stretch phase of growth prior to flowering.
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Q: What pH is best for nutrient feed and the medium?
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A: Between 5.5 to 6.5 pH is best. This is because optimal pH is required for nutrient uptake of macro and micronutrients such as nitrogen, phosphorus, magnesium (macro), and Iron (micro) between 5.5 and 6.5 pH. Molecules exist in different forms at different pHs and some forms the plant can uptake and others it cannot. If plants are not uptaking nutrients effectively this can lead to salt building up causing root burn, nutrient deficiencies, and root rot.
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Q: What is the importance of leaf picks?
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A: Always keep in mind light is one of two main drivers to plant photorespiration or photosynthesis (the other is a carbon source like CO2) you want to give all new growth access to the light, darker older leaves are less efficient at photosynthesis lighter leaves better for light absorption).
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Q: What is the point of adding mycos (mycorrhizae) to media?
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A:Mycos are short for mycorrhizae which is a type of fungus that forms a symbiotic (mutually beneficial relationship) with plant roots. This fungus is made of small roots that are able to make more contact and extend the reach of regular plant roots. Meaning they can increase the area plants are absorbing nutrients from in the media. They also are able to absorb nutrients not normally available to the plant like insoluble phosphorus.
Q: Why use silica?
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A: Though silica is not an essential plant nutrient it can be incorporated into the plant cell wall which can be beneficial for a variety of reasons. For example, it has been found supplementation for silica in the form of SiO4 can increase a plant's resistance to fungal infection as well as environmental stressors like extreme wind or heat. Though, it should be kept in mind that though it can help a plant, it is not necessary for growth.
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Q: What is the importance of runoff?
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A: Runoff keeps excess salt or insoluble nutrients from building up in the root zone. When no runoff is given the excess salt can create a toxic environment with unstable pH which leads to inaccessible nutrients, this can burn the roots, cause nutrient deficiencies, and increase the spread of pathogens.
When 'stacking nutrients' you can water several times over the course of a day or even a couple of days without a runoff, but it is NOT recommended to go over 2 days without runoff for the above-mentioned reasons.
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Q: Why is air movement essential and what method is the best?
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A: Air movement mimics wind in a plant's natural environment, which reinforces a plant's stability and stem strength, increases the rate and consistency of dry downs, increases the rate of transpiration, and decreases the likelihood of bacterial and viral build-up. This regulates transpiration by regulating the rate of gas and water vapor exchange between the leaf surface and the environment.
The best method of air movement is bottom-up, followed by top-down, with side airflow being the least effective.
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Q: What are the important factors for indoor growing?
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A: The environment created for indoor growing must maintain a high-quality balance between light, photoperiod, temperature, relative humidity, air circulation, and carbon dioxide level. (1) When growing outdoors these parameters are regulated by the biotic and abiotic factors in the ecosystem, plants have evolved for millions of years to best survive outdoors. The key to indoor growing is to mimic peak environmental conditions for growth and health.
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**** If you have any additional questions you'd like answered send a message this page is updated weekly!*****
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Media (Root environment):
Based on where you are growing (indoor, outdoor, greenhouse), the plant caring for (mother, seedlings, clone, vegetative, flowering), Desired cost, and the equipment necessary you can choose from a range of media for your roots to thrive in. This includes peat-based mixes, coir-based mixes, coir blocks,
preformed rock wool, and more. Here are some of the basics to consider about the most commonly utilized mediums.
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Rockwool
Rockwool is comprised of minerals that can be liquidized temperate like basalt rocks(3). Due to its method of production, rockwool comes completely sterile and free of microbes and other pathogens (3) though this can change over the plant's growth cycle It has great aeration, superb water holding capacity, is lightweight, a near-zero nutrient retention capacity, and CEC is also near zero. One of the major downsides to rock wool is it is not easily recyclable or reusable, and is generally seen as not environmentally friendly. (3) IT is also prone to nutrient leaching due to low CEC so when using this incorporation of nutrient fertilizer feeds is recommended.
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Coir-based
Coir is a growing medium derived from coconut shells and is utilized for hydroponic growth systems. There are a few forms that this media may come in such as expandable bricks the formulations include varying amounts of pith, fiber, and husk, dependent on a brand's proprietary recipe. In addition to Pure coir (loose), coir and perlite mixes. This media has high aeration and excellent drainage, which contributes to its popularity as a hydropic medium.
Coir holds water well (3) and has a high CEC (cation exchange capacity) which contributes to its ability to lock in certain positive ions like calcium, potassium, sodium, and magnesium (14). This is why prior to using any coir-based mix it is recommended to "wash" and buffer the media. "Washing" means rinsing the media until runoff with at least water to remove any material that may have accumulated. Buffering entails rinsing the nutrient solution of your choice until, so you saturate the media with your necessary amendments.
An environmental plus to Coir is that since is it a residue product from the coconut industry it is one of the most sustainable mediums (3).
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Peat Based
Peat is harvest material from sphagnum peat bogs in Canada and certain Eastern European countries (3). This medium is naturally acidic, hydrophobic, and low in nutrients. When it is distributed commercially it is typically incorporated with amendments like neutralizing agents, perlite, wetting agents, nutrient charge, etc. (3) depending on the company and proprietary blend. Peat has a high buffering capacity which is important to keep in mind when considering necessary fertilizers for your plant.
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Living Soils
Living soil is made up of medium mixed with microbial and mycorrhizal populations. The propriety blends of living soils vary greatly. Some of the basic components include peat moss, coir pith, coir chunks, naturally aged bark, wood fiber, compost, bacterial inoculants, mycorrhizae, and actinomyces (3). There are many benefits to living in the soil such as soil flora providing greater nutrient bioavailability and accessibility to the plant. However, it can be difficult to structure a living medium that maintains the proper drainage, aeration, and texture for your plant. It is also important to consider when fertilizer your medium you are feeding not just your plant but the diverse community of your soil.
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*Recommendations of growth stages are based on container growing using rock wool, peat-based mixes, and coir-based mediums. For more information on best practices or the basics of plant stages in living in soil contact us today or subscribe.
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The image on the left depicts clones in Rockwool.
The image above depicts a plant in one type of coir blend incorporating husk and pith primarily.
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The image to the right depicts the roots of a plant grown in a coir blend with a high ratio of pith
The image to the left depicts the roots of a plant grown in a peat-based mix which includes perlite.
The Basics of the Propagation:
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-Two of the most common ways to start a plant is from seed or clone cutting.
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-For whatever germination method you choose light intensity should be at its lowest. If you are growing indoors this equates to about a 150 PAR light intensity.
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-Also, for environmental conditions (outside of the dome):
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-Humidity can range from 65-70%
​-Temperatures should be kept between 73-80F which may be maintained during the entire vegetative stage.
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*For those growing outdoors seeds/clones should be rooted/germinated between March-April depending on your climate.(1)
Germination from seed
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- Seeds can be sown in a variety of mediums, as long as it allows for proper drainage, a common example is a mix of peat moss, perlite, vermiculite, and amendments just as mycorrhizae can help the establishment of roots and limestone can help manage the pH.
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- Seeds should be planted at a depth between 1/4 to 1/2 inch for optimal germination.
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- Domes should be kept on for approx. 24-36 hours to allow for optimal humidity during the time of germination. Domes kept on too long or after germination can cause unnecessary stress on the plants and can cause abnormal growth patterns.
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-Heating mats can help root establishment during the germination period but are not recommended after germination.
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- It is recommended to start seeds in smaller cells, depending on the size of the cells that seeds are planted in they can be transplanted approx. 1 month after germination. From seed cell plants can be placed into 1 gallons pots of the medium of your choice.
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- For those interested in topping plants, this can be done approx. one month after germination as well.
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Cloning- from stem cutting
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-This is the act of reproducing a new genetically identical plant off of a mother plant exhibiting the traits one desires for mass production.
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-Mother plants should be kept in the vegetative stage (18 hour light-6 hour dark) constantly.
-When choosing cuttings it is best to consider what end product you desire.
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-The freshest growth with light green growth, from the top of the plant is where the mother plant is the healthiest, cutting from this area will give you the healthiest clones possible.
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-This stem cutting should be done diagonally to increase the surface area for rooting.
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-A clone cutting should be at least 3-5 node points long.
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-After cutting leave at least 3-4 leaves at the top of the clone.
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Why? It is optimal for rooting and photosynthetic capacity because nodes are areas of meristematic growth or new growth. They transport plant hormones for cell determination to areas that need it most. Areas of new growth are present in the root zone and stem at areas where new branching for branches, leaves, and roots develop. The leaves supply light to the clone which it requires as a form of energy to produce the sugars to make hormones, so it is important that the leaves which remain on have access to light.
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- The medium for a clone cutting can be a rockwool clone cube or peat moss plug, these allow for the exposed injured area of the plant to remain wet while the roots are established. Enabling nutrient/water uptake to continue without the cutting having roots yet.
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- Before placing the clone cutting in your medium it is recommended you lightly scrape the base of the cutting. This also increases the surface area for roots to become established.
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-It is also recommended to use plant rooting hormone or IBA (indolebutyric acid), which is sold commercially, but it is simply the same chemical the plant produces to grow roots. By applying it at the area of injury/where the cut was made it increases the rate of rooting.
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-the clone cutting should be placed 3/4 of the way to the bottom of the Rockwool cube or peat plug so roots can escape when established but still maintain moist conditions.
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-After placing it in the medium the clone should be domed for optimal humidity. The dome should be removed after approx. 5 days, longer could increase the likelihood of pathogens spreading or stress on the cutting.
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- Roots should begin showing approx. 10 days after cloning.
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-On days 14-18, the clone should be planted, 1-gallon pots are recommended.
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-For those interested in topping clones this should be done approx. 2 weeks after roots are established.
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The image to the right demonstrates the first day of germination.
The image to the right depicts new 'adventitious' roots originating from the site of scraping near the lower node which prior to this photo was inside a medium.
The Basics of the Vegetative Stage:
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-Just like in germination and for mother plants, the light cycle remains at 18 hours of light and 6 hours of dark.
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The vegetative stage begins essentially after the plant germinates/roots begin to grow.
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-If you are growing indoors light intensity begins to increase. It is recommended this is done gradually. Starting at approx 250 PAR for the first week. Gradually increasing to about a 400-450 PAR range over the course of the next 7 to 10 days.
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-Humidity can range from 65-70%
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​-Temperatures should be kept between 73-80F which may be maintained during the entire vegetative stage.
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-This 400-450 PAR range should be maintained for the rest of the vegetative stage.
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-If one is using nutrient feed the ideal EC (or electrical conductivity) should be about 1.2-1.6EC.
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-An ideal watering cycle for plants in 1-gallon pots from transplant to flower should be approx. every 3 days for the first 10 days, 2 days for the next 4-8 days, then every day for the remainder of vegetative growth.*
*This can be subject to change based on excessive heat, decreased humidity, airflow in the room, and the strain/cultivar.
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-If topping the first topping should be completed by the 2nd week in the 1-gallon pot. As long as lighting and spacing between plants is optimal this should be the last topping.
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-This stage of growth should ideally be 28-35 days depending on the strain/cultivar. This will allow plants between 18-24in+ in height (again depending on the strain/cultivar).
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Above is a 22-inch plant at the end of a 32-day vegatative phase, derived from clone.
The Basics of the Flowering Stage:
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-The light cycle switches to 12hrs of light and 12 hours of dark. This switch induces flowering.
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-This stage lasts for about 2 months* (this can vary based on cultivar due to differences in requirements for Indicas and Sativas and their respective hybrids 2 months is average and one should always assess requirements for their particular cultivar)
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*For those growing outdoors the Flowering stage should begin around June.
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-An important difference between the vegetative stage and the flower is that watering should happen more consistently. Based on your irrigation strategy you can water or 'feed' plants up to 4-6 times per day. Typically when this is done small amounts of nutrient water are given to the plant (not enough for run-off) over the course of the day separated by 2-4 hours each time. If runoff is desired to avoid salt build up this is done during the last watering/'feed'. This practice is called 'stacking'.*
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-*Water requirements can vary based on the cultivar/strain, Sativas are known to prefer drier root zones than Indicas, and each strain may require varied nutrient inputs.
-* In addition pot size affects watering (often 1-3 gallons are utilized for container growing.)
-*The environment can also drastically change watering so if inputs fall out of the below-mentioned range so will watering consistency.
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-*If you are growing outdoors in the ground watering method, nutrient requirements, and environmental inputs will vary from the below parameters (this must be kept in mind)
(!!!When growing outdoors ORGANIC regenerative practices are highly recommended!!!)
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-If one is growing commercially and desires to LST (low-stress train) the branches using a trellis this should begin immediately after the plant starts the flowering stage.
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First 2 weeks(14 days)- This is when the plant first transitions from vegetative growth to flowering.
-Height increases substantially during this stage which is why it is referred to commercially as the 'stretch phase'.
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-The light intensity typically increases by about 300-400 par to about 700-800PAR.
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-Co2 requirements increase
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-Nutrient requirements increase to compensate for the increase in light and Co2.
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-The temperature range decreases slightly to 70-78F.
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-Humidity decreases to about 60-50%.
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-By Day 14- you'll start noticing the bud sites developing in the areas of new growth. This includes the apical meristem or top nodes for each branch, as well as nodes lower on the branch.
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-By Day 21-50 - Though the height of the plant continues to increase, energy allocation begins to shift from height to bud growth. The sites where bud growth began during day 14 will continue to increase in density.
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Nutrient inputs will increase overall. The most notable increases in potassium, calcium, and magnesium and decreases in nitrogen
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-Day 45-60- You'll notice the stigmas or 'hairs' on your buds begin to transition from white to a light orange or amber color. The leaves will begin to change from green to yellow, red, and purple resembling the trees outside during the fall. The buds should be at their maximum swell. The plant is now approaching harvest.
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-Nutrient feed (if used) begins to decrease in EC. Less nutrient feeds should be necessary and more runoff should be given to flush out excess nutrients.
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-If desired drought stress can be implemented (as long as regulated) to increase the plants production of its protective chemicals/secondary metabolites, these are cannabinoids and terpenes.
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-Specifically, drought stress week 6 of Flower can increase secondary metabolite levels by as much as 50%.
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-If drought stress is utilized it is important to stop stress/water plants when leaf wilting becomes noticeable.
-The environmental temperature should decrease to about 70-75F.
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-The humidity should also decrease to about 45-40%.
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-It is important to note that plants should not be harvested after the plant is ready, the amber color of the 'hairs' is a key indicator. If plants are kept for extra time cannabinoid and terpene content can begin to decrease dramatically, and you can increase the likelihood of pathogens infecting your buds.
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*For those growing outdoors harvest will occur between the months of August-November depending on climate, strain/cultivar, and date of propagation.
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Deficiency, Toxicity, Pests and Pathogens:
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Have you ever wondered why your leaves are beginning to turn yellow and you are still weeks away from harvest? What about unknown bugs wreaking havoc on your nugs? Well here are some of the key identifiers and reasons why your plants may be experiencing a type of stress, deficiency, toxicity, pest problem, or pathogen.
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For Reference a HEALTHY LEAF:
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Nutrient Problems:
Basics for Avoiding Nutrient Problems:
Check the pH of your media/run regularly:
Nutrients are only available to plants at specific pHs. This is one of the most common causes of nutrient deficiency
You can buy equipment specifically designed for checking the pH of your growing environment.
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Nitrogen (N)
-Mobile nutrient
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-Necessity:
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Nitrogen is one of the fundamental building blocks for plant growth. It is essential for the development of chlorophyll. Chlorophyll is what is responsible for the green coloration of leaves, its role is to absorb energy in the form of light in order to catalyze the process of photosynthesis. It is also a part of amino acids, which make up proteins in all living organisms(9)
-Deficiency:
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Deficiency will be shown in lower leaves or older growth. It will present as yellowing of the leaf. This is often caused
by soil low in organic matter for organic growing or low in fertilizer if growing hydroponically. This can also happen
if you are watering excessively without nutrient feed. (4,8)
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Solution:
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A major solution is to increase your use of organic matter or nutrient fertilizer. Note the minerals in your fertilizer is it
has multiple parts. If growing outdoors it would be beneficial to grow legumes, clover, or other nitrogen-rich and fixing
cover crops
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-Excess/toxicity:
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Leaves will become a dark deep shade of green, accompanied by excessive leaf growth. This is most noticeable during late-stage flowers you will see buds growing excess leaves as opposed to typical swelling.
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Phosphorus (P)
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-Mobile nutrient
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Necessity:
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Phosphorus is another one of the building blocks of proteins. It also contributes to the structure of nucleic acids like DNA and RNA which are responsible for storing genetic information in all plants and animals. Phosphorus also is a component of ADP and ATP which are responsible for energy transfer. (8)
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Deficiency:
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Presents on older growth/lower leaves as leaf yellowing and necrosis (death) starting toward the outer edges and progressing to overall leaf yellowing with gray necrotic tissue. (4,8)
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Solution:
a pH imbalance is a major reason for this deficiency. If growing hydroponically track your runoff and see if it is out of range. If it is too low or too high adjusting the pH of your feed accordingly is key. Lime is also a great pH stabilizer for people who are not using salt-based nutrient feed.
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Potassium (K)
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-Mobile nutrient
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Necessity:
Potassium initiates enzymatic reactions in plants. These reactions include protein synthesis, translocation, starch (sugar) storage, and new (meristematic) growth. (4,8)
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Deficiency:
Presents on older growth/lower leaves. It will begin as yellowing around the edges of the leaves, progressing to a browning around the edge of the leaf as the rest of the leaf continues to yellow. (4,8)
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Solution:
A common cause of this is the pH being too high, using soil amendment can remediate this. If watering without nutrient feed then decreasing the frequency of watering can also help. If watering with nutrient feed ensure the product you are using has adequate amounts of potassium.
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-Excess/Toxicity:
Also presents on older leaves will typically present as yellowing between the veins.(8)
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Secondary Nutrients-
Despite the name secondary nutrients are still essential for the health and development of your plants.
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Calcium (Ca)
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-Immobile nutrient
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-Necessity:
Calcium is essential for cell growth, division, and cell wall formation. Calcium also aids in the absorption of other nutrients via the roots, as well as activates enzyme systems that regulate plant growth. Calcium also neutralizes soil acidity. (4,8)
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-Deficiency:
Presents on new growth/upper leaves as brown spots running down the area between the veins of the leaf and the outer edge. (4,8)
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Solution:
Calcium deficiency often occurs when there is not an adequate nutrient supply. Try altering the watering schedule by either increasing or decreasing depending on the fertilizer you are using. Calcium carbonate and calcium nitrate are useful amendments.
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Magnesium (Mg)
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Mobile nutrient
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-Necessity:
Magnesium is a central part of chlorophyll*(see nitrogen for the role of chlorophyll). It is also a component of numerous enzymes. (4,8)
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Deficiency:
Presents on older growth/lower leaves as yellowing beginning at the edges of the leaf typically you'll notice the midvein remaining a lime green color. Tip burns and speckled necrotic tissue are also evident in this deficiency. (4,8)
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Sulfur (S)
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-Immobile nutrient
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-Deficiency:
Presents new growth/upper leaves as yellowing. This deficiency progresses uniformly across the leaf surface. (4,8)
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Micronutrients:
Deficiencies to micronutrients are incredibly uncommon if any of these deficiencies are present it is likely that they will be accompanied by macronutrient deficiencies as well.
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Iron (Fe)
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-Mobile
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-Deficiency:
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Presents as yellowing of new growth/upper leaves. Iron deficiency can be distinguished as it typically starts at the center of the leaf and moves outward to the leaf edges. (4,8)
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Manganese (Mn)
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-Immobile
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-Deficiency:
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Presents as yellowing of new growth/upper leaves. Unlike the other micronutrient deficiencies this also typicall presents with brown spotting.(4,8)
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Zinc (Zn)
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-Mobile
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-Deficiency:
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Presents as yellowing of new growth/upper leaves. A distinguishing trait is tip burn often accompanies this deficiency. (4,8)
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Copper (Cu)
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-Mobile
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-Deficiency:
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Presents as yellowing of old growth/upper leaves. (4,8)
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Boron (B)
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-Immobile
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Additional Factors:
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Salt:
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-Salt in the insoluble form of the aforementioned nutrients. It will exist in the root zone for a variety of reasons including out-of-range pH, excess nutrient feed, and lack of calcium.
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-Salt build-up can contribute to nutrient deficiencies, root burn, and root rot, decreased soil pH, and pathogen susceptibility.
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-Excess/Toxicity:
Salt build-up typically begins with brown 'burning' starting at the tip of the leaf and progressing down the leaf surface. It may occur in both old growth and progress to newer growth. Salt build-up can also stunt growth in terms of height and bud growth. Buds may also be burned with excess salt.
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Solution:
A quick fix to salt buildup is if you are using the nutrient feed, regular amendments, or organic fertilizer decrease frequency until symptoms resolve. Also, water (free of fertilizer) to rinse out excess salts in the root zone.
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An alternative reason for tip burn:
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-Excess light:
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If light inputs increase too dramatically, outpace nutrient feeds, or are excessive for a plant stage (e.g. flower PAR is used during the vegetative stage) tip burn may occur.
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-Excessive heat:
If the temperature is too high, tip burn may occur which will typically be accompanied by wilting even when the root zone is wet.
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Common Pests:
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Thrips:
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A key indicator of thrips is white and black speckles across the leaf surface. Thrips can live on the leaf surface as well as on the underside of the leaf. They appear as small, tan, opaque cylindrical insects that are visible to the naked eye.
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Thrips suck the nutrients out of leaves and buds and can over time significantly decrease crop yields. They are often difficult to get rid of once their colony has become established.
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Eradication & Control:
The best way to control this is to do regular pest scouting. Thrips enjoy spending time along the midvein of the leaf. Once thrip pressure has been identified it is recommended to start a regular foliar spray schedule approx. 3 days a week until pests can no longer be identified. When using spray apply to leaves and surrounding area, wait approx. 1 hour for the solution to dry and then use a 1: 1.5 gallon ration of tap water to rinse the solution. Ensure lights are off or the sun is down during this process to avoid leaf burn. It is best to check at the end of every week to reevaluate the severity of the infestation.
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DO NOT use insecticidal spray after day 14 of flower/or after budsites are present.
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Fungus gnats:
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A key indicator is small flies surrounding the medium/soil environment. Though adult fungus gnats don't damage the plant at all, their larval or infantile stage can drastically damage roots resulting in stunted plant growth (12). Adult fungus gnats are attracted to light, and they are known to breed in wet and nutrient-rich environments like wet medium, compost, and puddles.
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Eradication & Control:
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Yellow sticky traps are a good way to trap adult fungus gnat and verify their identity. Once you have identified your pest it is best to use a magnifying lens to inspect root zone for larvae. Using an insecticidal soap to drench the roots, waiting 1 hour between application and rinsing solution out of media until runoff is achieved can treat larve infestation. It is also recommended that plants are allowed longer to dry down to decrease the favorability of breeding conditions.
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-Spider mites:
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A key indicator is the webbing they produce similar to that of a spider. To the naked, they appear as small, moving dots beneath the leaf surface. These are best viewed through a magnifying glass or microscope 10x and higher. These mites thrive in hot, dry, and dusty conditions (12). They cause damage by sucking the nutrients out of the leaves. When it comes to cannabis they pose the biggest risk by infesting buds which can leave the flower unsalvagable.
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Eradication:
Once identified it is best to start a regular foliar spray approx. 3x per week using insecticidal soap. When using spray apply to leaves and surrounding area, wait approx. 1 hour for the solution to dry and then use a 1: 1.5 gallon ration of tap water to rinse the solution. Ensure lights are off or the sun is down during this process to avoid leaf burn.
If the population continues to grow or to the termination of the plant and any surrounding plants that may also present signs of infestation.
DO NOT use insecticidal spray after day 14 of flowering/or after budsites are present.
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If the problem continues to grow or pests are spotted after bud sites present termination of the plant and any surrounding plants are highly recommended.
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Getting rid of pests:
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-Organic pesticides:
Examples include Green Clean, Plant Therapy, Dr. Zymes
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-Maintaining a clean growing environment. Pests often breed in sitting water.
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Beneficial:
Nematodes (Steinernema feltiae) - These biologicals reproduce exponentially while searching for pests continuously. Once applied they can stay indefinitely if conditions stay warm and moist. They are best applied via a soil drench or using spray equipment, through several applications.
Common Plant Pathogens:
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Powdery Mildew:
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Powdery mildew includes several species of fungi (Erysiphe spp., Sphaerotheca spp.). It presents as white blotches across the surface of a leaf. This fungus thrives in temperatures between 60-80 degrees Fahrenheit and in shade, spores are spread via wind.
Growth and germination of spores are inhibited by water on the leaf surface (12).
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Eradication:
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Fungicides are the best method of removal in addition to water application on the leaf surface.
Powdery mildew as a mold is a major NO-NO when it comes to commercial cannabis as infection of the bud as a finished product can lead to major health problems. If powdery mildew is found in your grow it is best to eliminate any plants where symptoms are present and any surrounding plants. For indoor and greenhouse grows make sure that the grow room is cleaned thoroughly after plant removal, use of 10% bleach solution is recommended.
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Root Rot (Fusarium spp.Pythium spp., Phytophthora spp., Rhizoctonia solani) :
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There are a number of root zone-dwelling fungi that cause root rot. Brown slimy roots are a key characteristic of these
pathogens. Root rot can stunt plant growth and eventually lead to plant death. (13)
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Solution:
Do not over-water. These fungi thrive in water-logged soil the easiest and best way to treat them is to increase dry-down
periods.
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Hop Latent Viroid:
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(Download Powerpoint below on Hop latent viroid)
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-Depending on the pathogen organic pesticides may be able to assist in remediation at early stages but for most it is likely best to kill the plant where symptoms are presenting and sterilize the area using at least 10% bleach to prevent the spread.
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-ALWAYS use gloves when handling plants to prevent the spread of pathogens!
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The figure above depicts the ideal pH range for the uptake of all required micro and macro nutrients.
The image to the left demonstrates late-stage nitrogen deficiency, the leaf was found at the bottom of the plant near the soil zone. Note the overall yellowing of the leaf
The image to the left depicts late stage potassium deficiency. Note the yellowing of the outer edges of the leaf and tip burn.
The image to the left depicts late-stage Phosphorus deficiency. Note the extreme discoloration ranging from yellow to brown and blackish grey.
The image above depicts early-stage calcium deficiency. Note that this is present at the top of the plant near new/meristematic growth. You'll notice discoloration starting as a burned yellowish color along the leaf surface
The image above depicts late-stage calcium deficiency. Notice discoloration region is much longer than in early-stage deficiency. The color also progresses to a deeper shade of brown as the leaf tissue dies back.
The image to the left shows stage Magnesium deficiency. Note this leaf is towards the bottom of the plant and is presenting yellowing starting at the outer edges of the leaf surface. Also, notice tip burn with speckled necrotic tissue.
The image to the left depicts a spider mite infestation on a pea plant (Pisum sativum) leaves. Note speckled necrotic tissue where nutrients have been sucked from a leaf. You can see the characteristic webbing of the mite also.
The image above to the left shows early-stage powdery mildew on the leaf of a summer squash (Cucurbita pepo). Powdery mildew is common in the Cucurbita family. Notice the white blotches on the edges of the leaf surface.
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The image above to the right shows late-stage powdery mildew on the same summer squash plant, notice how the overall coloration of the leaf has changed.
The image to the left depicts a dead fungus gnat on the surface of a healthy Cannabis leaf.
The image to the left demonstrates late-stage thrip damage. Notice the combination of black dots and white splotching across the leaf surface in addition to necrotic brown tissue at the leaf tip where the nutrients have been drained the most.
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If you look closely you can see 3 thrips down the midvein of the leaf.
The image on the left is late-stage sulfur deficiency. Note that the deficiency is presented at the top of the plant at the place of new growth, with overall leaf yellowing.
Solution:
A common cause of magnesium deficiency is low pH. Altering the pH of your nutrient feed or adding lime you your media is a great solution. Also, since magnesium is a mobile nutrient it can be treated via foliar spray. This is done by adding liquid fertilizer mixed with tap water to the surface of the leaves. Be sure this process is done with the lights off to avoid salt burn. After leaving the application on for at least an hour/ until it dries rinse off with tap water, let the tap water dry before turning the lights back on or before the sun comes up.
Solution:
Adding organic matter like compost can aid in this deficiency. If growing using fertilizers like those used in hydroponic environments addition of ammonium or calcium sulfate can also aid in remediation.
The image on the left shows the roots of a plant at the beginning stages of root rot. Note the transition from the root's healthy white coloration to tan.
Post Harvest / Cure
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The Cannabis 'bud' needs specific care after it is harvested for an extended period of time in order to dry down enough to be smoked while still maintaining its heat and light-sensitive chemicals like terpenes and cannabinoids.
Harvest:
Beginning at least 3 days prior to until you are at the time of harvest, you should pick as many large fan leaves off as possible. You can leave on 'sugar leaves' or leaves that are directly attached to the base of the bud as long as the material is not necrotic.
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Immediately after harvest the Cannabis Inflorescence 'Bud' has a moisture level between 70-80%. (7)
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By the end of the curing which typically takes an additional 2 weeks after the post-harvest/ drying period the moisture of your bud should be between 8-13%.
Post Harvest:
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Ideal conditions for your curing environment are as follows:
It should be dark with good air exchange
45% - 65% Humidity (7,11)
64 F - 69 F for the first 5-10 days (7) depending on dry down.
The moisture should be between near-ideal moisture levels 8-13% by the end of drying prior to being placed into containers.
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Cure:
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59 F-68 F loosely in airtight containers after that (7)
If the environment is too hot or dry, the bud will dry faster and terpenes will be lost as they are heat-humidity sensitive.
If the environment is too humid then you can increase your chances of getting mold, in addition to other fungal, bacterial, and viral pathogens.
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References:
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1. Chandra S, Lata H, ElSohly MA. Propagation of Cannabis for Clinical Research: An Approach Towards a Modern Herbal Medicinal Products Development. Front Plant Sci. 2020;11:958. Published 2020 Jun 26. doi:10.3389/fpls.2020.00958
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2.McPartland JM. Cannabis Systematics at the Levels of Family, Genus, and Species. Cannabis Cannabinoid Res. 2018;3(1):203-212. Published 2018 Oct 1. doi:10.1089/can.2018.0039
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3. Nemati R, Fortin J-P, Craig J, Donald S. Growing Mediums for Medical Cannabis Production in North America. Agronomy. 2021; 11(7):1366. https://doi.org/10.3390/agronomy11071366
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4. Cockson P, Landis H, Smith T, Hicks K, Whipker BE. Characterization of Nutrient Disorders of Cannabis sativa. Applied Sciences. 2019; 9(20):4432. https://doi.org/10.3390/app9204432
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5. Caplan D, Dixon M, Zheng Y. Increasing inflorescence dry weight and cannabinoid content in medical cannabis using controlled drought stress. HortScience. 2019;54(5):964-969. doi:10.21273/hortsci13510-18
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6.Luyckx M, Hausman J-F, Lutts S, Guerriero G. Silicon and plants: Current knowledge and technological perspectives. Frontiers in Plant Science. 2017;8. doi:10.3389/fpls.2017.00411
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7. Zheng Y. Handbook of Cannabis Production in Controlled Environments. CRC Press; 2022.
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8. Nutrient deficiencies in plants. Extension. Accessed August 23, 2023. https://extension.wvu.edu/lawn-gardening-pests/plant-disease/nutrient-deficiencies-in-plants.
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9. Wagner, S. C.. (2011) Biological Nitrogen Fixation. Nature Education Knowledge 3(10):15
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10. Secondary nutrients: Nutrient management. Mosaic Crop Nutrition. July 5, 2023. Accessed August 23, 2023. https://www.cropnutrition.com/nutrient-management/secondary-nutrients/.
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11. Christianson C. Terpene boiling points and temperature. True Labs for Cannabis. January 19, 2022. Accessed August 26, 2023. https://www.truelabscannabis.com/blog/terpene-boiling-points#:~:text=Some%20terpenes%20will%20begin%20to,product%2C%20but%20also%20its%20effects.
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12. How to manage pests. UC IPM Online. Accessed August 28, 2023. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7448.html.
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13. Root rots on houseplants. Wisconsin Horticulture. Accessed August 30, 2023. https://hort.extension.wisc.edu/articles/root-rots-houseplants/.
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14. What Is Coco Coir? - Washing vs Buffering, www.shogunfertilisers.com/en/growing-information/blogs/what-is-coco-coir-washing-vs-buffering/#:~:text=The%20average%20CEC%20of%20coco,important%20cations%20when%20buffering%20Coco. Accessed 30 Aug. 2023.