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Cannabis has different nutrient requirements from strain to strain and particularly during the vegetative and flowering periods.
Cannabis requires both macronutrients (i.e. nitrogen, phosphorus and potassium) and micronutrients (i.e. calcium, sulfur, magnesium, copper, iron, manganese, molybdenum and zinc) for successful growth.
Most commercially available soils have fertilizers and nutrients in them and will not normally require additional fertilizers and nutrients during the first month or two of growth.
Cannabis normally requires the use of more nitrogen (N) during the vegetative growing cycle. During the flowering cycle cannabis will normally require an increase in phosphorus (P). Nitrogen (N) requirements also vary with light intensity and temperature. During “Hot” conditions (more than 90 degrees Fahrenheit) the plants will require 10 to 20% less nitrogen. During cool periods (less than 60 degrees Fahrenheit) the plant will require 10 to 20% more nitrogen. Intense light (greater than 80 watts per square foot) the plants will require more nitrogen (N) and for low light conditions (less than 25 watts per square foot) the plants will require less nitrogen (N).
Watch the plants closely for any changes or signs of nutrient deficiencies and disorders.
Soil Based Products and Cannabis Nutrients
Compost teas work best in soil-based systems, because the solids and particulates that make up the tea can cause problems with hydroponic equipment. Organic fertilizers and additives that can be used in soil-based systems are:
Ammonia – (NH3) is a gas containing 82% nitrogen. Often used as a foliar feed in its aqueous form.
Cottonseed Meal -A byproduct resulting from the extraction of oil from cottonseed with a nitrogen content of 67%. Generally it is used as a partial source of nitrogen in mixed fertilizers.
Blood Meal – Blood meal is a byproduct of the meatpacking industry and has a nitrogen content of 12 to 14%. The nitrogen is available in a short time, but it does little for the mechanical properties of the soil.
Urea – Urea is a white crystalline compound containing 46% readily available nitrogen.
Fish Emulsion – Fish emulsion is prepared from non-edible fish and waste from fisheries. It has about 8% nitrogen.
Bone Meal – Two kinds: raw and steamed. Steamed bone meal has less nitrogen than raw, but more phosphoric acid. This material releases its nutrients slowly so it can be used without fear of injuring the crop.
Rock Phosphate – Mineral occurring in deposits throughout the world. Its effectiveness is dependant on its degree of fineness, and the reaction of the soil.
Super Phosphate – A source of phosphoric acid in complete fertilizers and a direct treatment of soils deficient in phosphorous but well supplied with nitrogen and potassium.
Slag – Finely ground byproduct of steel manufacture. Its free lime content makes it of special value in the reclamation of acid soils.
Wood ashes – Rapidly absorbable form of potassium that will lower pH.
Seaweed – Contains a host of macro- and micro-nutrients, helps in water retention and absorption, and aids in weed prevention.
Growth and Flowering Supplements and Additives
There are more cannabis growth supplements, bloom supplements and stimulants, root stimulators and additives available than can be easily described here. All supplements and additives must be added with caution to prevent any nutrient disorders, over-fertilization or nutrient burns. We will provide an overview of what is commonly available.
Fulvic Acid – used as growth stimulators. Fulvic acid is a natural acidic organic polymer that is extracted from humus found in soil, sediment, or aquatic environments.
Humic Acid – a principal component of humic substances, which are the major organic constituents of soil, peat, coal, many upland streams, lakes and ocean water. It is produced by biodegradation of dead organic matter. It is not a single acid; rather, it is a complex mixture of many different acids.
Gibberellic Acid – a hormone found in and extracted from plants. It is a naturally occurring plant growth regulator, which may cause a variety of effects including increasing the number and size of buds and the stimulation of seed germination.
Amino Acid – the key elements are carbon, hydrogen, oxygen, and nitrogen. Amino acids are critical to life and have many functions in metabolism. One particularly important function is to serve as the building blocks of proteins.
Enzymes – proteins that increase or decrease the rates of chemical reactions. At this time there are limited products available that claim to promote the use of enzymes for improving and increasing the growth of medical cannabis.
Carbohydrates – plants require sugar and carbohydrates in order to have enough energy for intense flowering periods and rigorous growth. The logical solution would be to just add sugar to the nutrient solution right? Many have tried this and often molasses is used as a simple sugar additive. The problem with this is that the sugar is not as easily taken-in by plants in this form. It is better to add a carbohydrate additive, which is designed to make these carbohydrate supplements easier for the plant to take in. By using these additives, a grower can expect the plants to have sweeter tasting fruits, increase their essential oils, and nourish the plants to prepare them for intense flowering periods. If possible look for a carbohydrate additive that is organic, and combines easily with the rest of the nutrients being used.
Silica based product – promote healthier and stronger plant growth. When the roots take up silica, it is deposited in the cell walls of the plant as a solid, rigid ‘quartz-like' matrix. This produces a ‘mechanically’ stronger plant, which enables superior leaf orientation and therefore greater rates of photosynthesis and growth. It increases the weight and shelf life of fruit due to the physical accumulation of silica in plant cells. Silica increases a plants tolerance to heat stress or “wilting”. It also increases resistance to fungal diseases, particularly mildews and botrytis. It resists fungal ingress by accumulating around the points of fungal attack. Silica improves the healing rate and neatness of pruning wounds. This property is especially beneficial in commercial cropping of plants such as medical cannabis. Regular pruning of these species threatens the plant's survival due to the risk of disease penetration through the site of the pruning wound. Finally, silica increases a plant’s tolerance to nuisance chemicals such as sodium and chloride.
Vitamin supplements – help a plant feel better when stressed and keep a plant healthy. Vitamins will help with resistance to fungal rots and insect attacks. While plants normally manufacture vitamins for themselves, if they have an external additional supply of them, they can then turn their energy to producing other elements they need, and thereby speed up growth.
Minerals – There are many minerals that are either required by the needs of the plant or are beneficial for improving the growth of the plant. Below are a few descriptions of minerals available for use.
Calcium-when added to the plants nutrient solution or to the soil it will improve the efficiency of nutrient uptake and encourage superior flowering.
Citric acids – can be added as a chelator (binder) for improved availability and plant uptake of nutrients and fertilizers.
Sulfur based additives – will activate enzymes, process compost and manure fertilizers, liberate roots systems and help balance soil pH.
Mycorrhiza – this is the relationship between the plant roots and beneficial fungi. Mycorrhizal products increase plant growth, nutrient and water uptake and improve soil structure.
Manufacturing Compost Tea
Compost tea for cannabis can be easily made by soaking or steeping compost in water. The resulting compost tea is used for either a foliar application (sprayed on the leaves) or applied to the soil. We all know that compost is a wonderful addition to soil and helps gardens grow better. The plants can benefit even more by using compost tea.
Using compost tea to replace chemical based fertilizers, pesticides, and fungicides, makes the cannabis garden safer and is more protective of the environment. Compost tea:
-Increases plant growth
-Provides nutrients to plants and soil
-Provides beneficial organisms
-Helps to suppress diseases
-Replaces toxic garden chemicals
2 five-gallon buckets
1 gallon mature compost
1 aquarium pump
1 gang valve (to divide the air supply into several streams)
4 gallons of water
3 feet + of aquarium hose
Attach 3 separate pieces of hose at least 12″ long to the gang valve.
Place the gang valve onto the bucket and make sure the hoses reach the bottom of the bucket. Weigh down the ends of the hoses with weights or small rocks taped or wired to the end of the hoses so that they remain at the bottom of the bucket.
Add the finished mature compost and make sure the ends of the hoses are covered. Add the water, filling the bucket to within 6 inches of the top. (NOTE: If using water from a public water source, run the pump and bubble air through the water for at least an hour before adding the water to the compost. This allows any chlorine to evaporate. Chlorine can kill beneficial organisms in the tea).
Add 1 ounce of unsulfured molasses to provide a food source for the beneficial microorganisms. Turn on the aquarium pump and let the mixture brew for 2 to 3 days. Stir the brew occasionally to help mix the compost and separate the microorganisms from the solid compost particles. After brewing the mixture, strain the tea. Use cheesecloth and strain the tea/compost mixture into another bucket. (Put the compost solids back into the compost pile or in the garden).
The tea should smell sweet and earthy. If it smells bad, do not use it on the plants, but dump the mixture back into the compost pile. Apply the compost tea to the plants immediately. The beneficial microbes will begin to die shortly after the air source is removed. Sprinkle the compost tea onto the foliage and the soil around each plant. The tea will provide nutrients and an energy boost to the plants. Apply compost tea every two weeks to the garden.
Mixing Growing Medium (soil)
There are many commercially available soil mixes on the market that have been specifically developed for growing cannabis both indoor and outdoor. These can be easily found online or at the local grow supply store.
For the experienced grower who chooses to mix their own soil, consider using this as a starting point for creating cannabis grow medium (soil):
50% Premium Potting Soil
20% Bat Guano High Phosphate Fertilizer
10% Organic Seafood Fertilizer
05% Sand (optional)
05% Organic Mix roots, bark, etc.
Add more if a deficiency occurs in flowering. It is highly doubtful that it will, but if it does, use a diluted foliar feed.
3 lbs. Bone Meal
1 cup Dolomite Lime
2 tbsp. Humic acids are highly recommended.
Apply as recommended per the manufacturer’s instructions.
5 lbs. Bat guano
2 five-gallon scoops Perlite
The use of a particle or dust mask is highly recommended to avoid breathing in clouds of dust.
It is recommended that all the ingredients be mixed together in a large barrel with a tight fitting lid, so as NOT to breathe in any dust or particles. Roll the barrel around to mix the ingredients. If mixing the grow medium without a barrel with a lid and instead mixing the ingredients in an open container, a particle or dust mask MUST be worn. Slightly moisten the ingredients to help avoid creating too much airborne dust and particles as the ingredients are mixed.
Some of the leading brands of cannabis nutrients are:
These are some of the best cannabis nutrients on the market today.
To learn how to grow robust, healthy cannabis plants from seed to harvest, enroll in Cannabis Training University's marijuana courses.