How to Make Your Own Cannabis Planting Mix to Maximize Your Marijuana Harvest
Cannabis roots photo by Purple Caper Seeds
Let’s think about roots for a moment. We don’t see them since they are underground, so we hardly ever pay attention to them and often take them for granted. We rarely consider what roots do.
Roots hold the plant in an upright position by branching out and clinging to the media, forming a strong network attached to the stem that braces it against environmental stresses such as wind and rain.
In addition to holding the plants up, roots supply them with water and dissolved nutrients. In a complex process the plant absorbs water by maintaining a higher level of salts than the surrounding soil. Water moves through pores in the roots to lower the concentration in the plant. The same process is used to move water from the roots to the stem and leaves. The roots’ pores act as selective barriers to nutrients to maintain this equilibrium.
“In order for roots to thrive they require suitable conditions. They must have access to oxygen, water, and nutrients, and be able to grow into the planting mix.”
Roots maintain a relationship with other organisms to form a symbiotic community. For instance, some mycorrhizae grow hyphae that enter the roots. Other organisms are free-living or form a shield around the roots. These other organisms supply the roots with dissolved nutrients the plant requires, and the plant roots supply them with food, the sugars produced during photosynthesis.
Outdoors, a well-draining fertile soil high in nutrients may need no additional preparation. This is not usually true in soils that have not been used in productive gardens because naturally growing plants don’t require the same amount of fertility as intensively cultivated crops.
Soil is a complex mixture of clay and other weathered minerals, sand, and digested organic matter, as well as myriad variety of organisms, including plants (roots), insects, and other arthropods, fungi, bacteria, and organisms representing other kingdoms. It is so complex a mix that we cannot create it from scratch. However, we can make planting mixes that provide the roots with a healthful environment that promotes a healthy, vigorous plant.
What are the perfect conditions roots require to thrive?
Marijuana plant in raised bed filled with planting mix.
POROSITY AND STABILITY
Cannabis roots require a media that is loose enough for the roots to grow through and form a network to hold the stem upright. Media that is too loose can injure the roots by allowing them to break free from their bonds. As it is colonized by the community of organisms that earn their livings by digesting the organic matter and by providing nutrients to the roots in return for plant exudates such as sugars and other plant products, the community collectively forms a “glue” that holds the particles together.
DRAINAGE
The media must drain well. Media that becomes compacted or soggy prevents air from getting to the roots since there is not much space between particles. It’s not that the media holds too much water, it’s that it doesn’t hold enough air. Unlike leaves that use carbon dioxide as an ingredient of photosynthesis, roots require oxygen for survival and are injured and die under anaerobic conditions.
When water is added to the top of a well-drained mix or soil it starts to percolate down. The medium’s particles grab the water to the point of saturation before they let the rest continue down. In containers the pressure of the water pushes air in the soil down. When water flows from the container’s bottom holes the air is also drawn down by the venturi effect. As the water flows down it creates a vacuum starting at the top of the container. It pulls air into the container as it flows down.
Learn more about Fusarium Root Disease and how to prevent it.
Outdoors, sandy and loamy soils that contain only small amounts of clay drain well and provide a good place for roots to grow. Clay is composed of tiny, closely connected molecules of mostly aluminum and silica that form dense sheets, so the clay becomes plastic when wet but hardens as it dries. When they’re found in small percentages in sandy or loamy soil they help it to hold water and to maintain a stable texture that resists erosion. When soils contain large quantities of clay they drain slowly and hold so much water that air is forced out.
NUTRIENTS
Planting mixes contain nutrients only if they have been enriched. You can grow in a medium with no nutrient value of its own such as coir, peat moss, or bark, or a mineral media such as vermiculite or perlite. All of these mediums support microbial growth once they are irrigated with a water nutrient solution. However, I think plants do better when the planting mix itself contains nutrients. The mix that we are making is enriched with compost as well as added nutrients so the plants will be getting nutrients both from the soil itself as well as from the nutrient/water solution.
Why you want to make your own planting mix for cannabis plants
The compost process uses both bacterial and fungal decomposition as well as red worms, and sowbugs.
Most commercial mixes are made primarily from one base ingredient, usually peat moss or bark. A few contain coir either as the primary base or as an additional ingredient. Most mixes also contain nutrients that may include plant meals, minerals, and animal products.
“The reason I prefer to make my own mixes is that I prefer not to grow in mixes that contain peat moss, forest products, or dead animals.”
Three reasons not to use peat moss in your marijuana planting mix
It loses its structure quickly, and under pressure in large containers it compresses, sometimes creating anaerobic conditions. When a mix goes anaerobic it develops an acrid ammonia odor.
It has a low pH, and even after it is adjusted with lime, its pH gradually sinks so it constantly needs adjustment.
It is un-ecological. Peat bogs are part of the north temperate environment. Despite the public relations propaganda showing how ecological strip mining these bogs is, I just don’t think it’s a sound practice to strip the bogs, use the peat moss for a few months, and then dump it in a landfill.
“Rather than using potentially harmful ingredients I prefer to use plant ingredients and sterilized manures to provide nutrients.”
Bark is a by-product of the timber industry. Although trees are not felled for their bark it still has its ecological impact because the sale of the by-product makes forestry more profitable. Bark is more pH neutral and takes longer to decompose, so it maintains its structure longer than peat moss.
Ripened compost is sieved through a half inch screen.
The reason I don’t like animal products such as bone or blood meal, leather meal or tankage, is the bad reputation these products have in relation to diseases such as mad cow disease, pathological E. coli bacteria, and other chronic conditions and diseases. For instance, researchers found that E. coli can be transferred from infected fertilizers and nutrients through plants to humans. Mammal manures are supposed to be composted for six months before being used, but this step is often shortened or skipped, potentially leaving bacteria active. Even chicken manure, previously viewed as very safe, is now regarded with some suspicion since the emergence of bird flu and other fowl diseases.
Learn more about what the dangers are for Microbial Contaminants in Cannabis.
The final reason I prefer my own mix is that frankly I think that I use a higher grade of ingredients than is supplied in most mixes to create one that has customized water - and air - holding capacity.
The Base Ingredients you need to make a planting mix for your marijuana
The Base is: Coir, Perlite, Vermiculite, and Compost
Food waste, garden clippings, and small quantities of used planting mix are the ingredients placed in the compost bin. The bin, which is about a cubic yard, takes about a year to fill, and then it ripens for another year.
COIR
Rather than using either peat moss or bark we will use coir as part of the base. Coir is the outer husk of the coconut. It is by far the most ecological soil base because it is a farmed by-product of coconut production that has not been used economically. Until recently it was considered a waste product that accumulated in gigantic piles. Now indoor agriculture has created a use for it.
Coir is pH neutral and holds its structure for a long time. It comes as large or small chunks, broken separated fibers, or finely chopped pieces. Depending on which portion of the coconut shell is used and how it is processed coir has different qualities of water-holding and absorbency. It holds its structure longer than peat moss so it can be re-used a number of times and can help maintain long lived plants such as mothers or slow flowering sativas. I recommend using different coir products for the entire base since they can be processed for different water- and air-holding qualities. However, most of these coirs are not readily available, so we will use the standard coir fiber available in shops and blend it with perlite and vermiculite.
Making compost: Twigs and other partially composted material are returned to the bin for further decomposition. Any stray plastic or debris is removed.
PERLITE
Perlite is made by heating volcanic hydrated obsidian glass. When it is heated to about 1500ºF, the water in the mineral evaporates and the glass expands into a porous lightweight state, much like what happens to popcorn. The expanded material does not absorb water but holds drops of water on its irregular surface. It keeps its structure in the mix to provide air spaces for water movement. It is chopped to pieces ranging from sand to pea size.
VERMICULITE
Vermiculite is made from silicate clay that is exfoliated using heat. The mineral naturally forms thin layers on top of each other that expand when heated, creating spaces between the layers that hold both water and air. It has a high cation-exchange capacity so it buffers acids well and helps keep the mix balanced. The mineral is soft and somewhat spongy when compressed. It has been used for growing for more than 50 years.
COMPOST/WORM CASTINGS
The compost process uses both bacterial and fungal decomposition as well as sowbugs. and red worms (as shown above).
I recycle all my food waste including flesh into my compost pile. In addition, I use green garden waste such as weeds and dried leaves including processed cannabis leaves. The pile, actually two one-cubic-yard compost containers, processes the waste over a two-year period. First one container is filled. This is done gradually as the garden and kitchen yield ingredients to compost and takes about a year. Then I start to fill the second bin. After I add a layer of new waste to this container I take the top layer of compost from the first container then cover the new additions with dried garden leaf and debris. I add new layers almost weekly.
While the active pile is composting the size of the material shrinks so that at the end of the second year the second pile is filled and two thirds of the aging compost has been used to cover the new pile. This leaves a pile of mature aged compost of about one third a cubic yard or nine cubic feet. A cubic foot is equal to 6.4 gallons. I sieve this compost through a half-inch framed screen to remove larger particles, leaving only grit-sandy compost that contains some dead plum pits. The pits don’t deteriorate for a long time and they provide some larger particles to the mix.
The pile is active and heats up a bit at times, but not to the pasteurization temperature of 160ºF. However, there is a large community of worms that turns the compost partially into worm castings. The nutrients they contain are readily available and are enriched with helpful enzymes while passing through the worms’ digestive systems.
The additives you will need for your cannabis planting mix
Additives: Activated charcoal, Alfalfa meal, Bat guano, Coffee grounds, Greensand, Iron-Zinc-Manganese chelates, Kelp meal, Mycorrhizae mix, Soft rock phosphate, Trichoderma, Volcanite Rock Dust®
Plants in commercial planting mixes at Dennis Peron’s garden in San Francisco. Dennis uses mostly smaller containers so he can move them around to follow the sun. He re-uses the planting mix, adding new material each time.
ACTIVATED CHARCOAL
Helps buffer the mix by absorbing excess nutrients and chemicals and may have other benefits in keeping the mix adjusted. Charcoal is associated with healthy plants.
ALFALFA MEAL
Contains 2.5 percent Nitrogen (N) as well as 1 percent Phosphorous(P) and 1 percent Potassium(K). It also contains natural plant regulators such as triacontanol.
BAT GUANO 10-3-1
Contains readily available N as well as small amounts of P and K. (I recommend using any combination of guanos including bat, seabird and cleaned poultry manure, to obtain high amounts of N and P.)
COFFEE GROUNDS
Contains 2.2 percent N as well as minor amounts of P, K, Magnesium (Mg) and Copper (Cu). The nutrients become available over a period of several months.
GREENSAND
Contains 25 percent Silicon (Si), 15 percent Iron (Fe), 7 percent K, 3 percent Magnesium.It is a sandstone called glauconite, the name given for iron-rich silica minerals. It gradually weathers, releasing its nutrients.
IRON(Fe)-ZINC(Zn)-MANGANESE(Mn) CHELATES
Chelated minerals increase the content of these minor nutrients quickly.
KELP MEAL
Contains 3 percent N that releases gradually.
MYCORRHIZAE
These are the beneficial fungi that develop symbiotic relationships with the roots. They form a major portion of the rhizosphere community surrounding the roots.
SEABIRD GUANO—0-10-0
This is a fast acting fertilizer that provides needed P to the soil. Bird and seabird guanos can be substituted with each other or with cleaned poultry manure (3-2-1) or insect frass to build up N-_p_K values.
SOFT ROCK PHOSPHATE—0-12-0
Contains an insoluble but easily available source of phosphate as well as an equal amount of lime. It gradually releases the nutrients as the plant uses them.
TRICHODERMA
Trichoderma is a species of very active fungi which protects plant roots from pathogens. They are found in the product RootShield®.
VOLCANITE ROCK DUST®
Contains a combination of rock dusts including granite and minerals. Rock dusts seem to enhance growth and plant vitality.
Recipe to make your own cannabis planting mix
3½ GALLONS of each:
Coir
Perlite (Size—Grade 3)
Vermiculite (Size—Grade 3)
2½ GALLONS:
Compost/worm castings
2 CUPS:
Activated charcoal
¾ CUP of each:
Alfalfa meal
Bat guano
Greensand
Kelp meal
Seab9ird guano
Soft rock phosphate
Coffee grounds
½ CUP of each:
Volcanite Rock Dust®
Iron-zinc-manganese chelates
1/8 CUP of each:
Mycorrhizae mix
RootShield®
I place all of the ingredients into the cement mixer that I converted into a soil mixer by never having mixed cement in it. Then I let the mixer do its thing for a few minutes. The result is about 13 gallons of grade AAA planting mix, ready to pour into a container.
Here are the analytical results for the soil
The analysis shows that the planting mix is pretty close to perfection for a high-energy crop. I did forget to add dolomitic lime, so it’s low in calcium and magnesium, both of which are essential for healthy, high-output, high-octane bud. I will resolve this deficiency using Cal-Mag and liquid lime when I irrigate the plants. The same goes for the low manganese, which will be resolved using manganese chelate.
Analysis: Soil (Worm Castings/ Compost)
You might have noticed that the N and P ratings are low. There is a reason behind this madness. Rather than loading the planting mix with high N and P material during vegetative growth and then trying to leach out the N during flowering, the soil is designed to be able to customize the amount by supplying most of it through the water/nutrient solution. This way the plants can get high N during vegetative growth, but during flowering, when their need for P increases (while their need for N decreases), the irrigation formula can easily be changed so the plants get exactly what they need.
“The planting mix feels good to the touch. It holds moisture and air, hardly clumps and has a very mild, pleasant odor. All of my plants thrive in it.”
Learn more about How to Start Cannabis Seeds Right.
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