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Class 207: Cannabis Soil

We are starting our outdoor flowering cycle, and it is very exciting to have beautiful weather in Arizona right now. We will be exploring the how-to’s and have our moments of checking-in on the grow but I was hoping to explore some concepts more in-depth. A subject I’m often asked about would be the amending or building of soil using all natural resources. In this article, we will cover many aspects of creating a soil that will benefit your cannabis most while also keeping it naturally sourced. We will explore the basics of worm farming for castings and explore the basics of vermiculture. Everything we cover here can be further explored and supplies sourced at my hydroponic shop of choice, Sea of Green in Tempe, AZ!

Good in, Good out

Cannabis has certain needs, and does not do well in most commercial potting soils for a variety of reasons, examples of such are poor water retention or drainage. These commercial mixes also do not have the bioreactive components needed because they usually lack the right amounts of the big three nutrients that cannabis needs. Those big three, Nitrogen, Potassium, and Phosphorus are usually listed in ratios on the front of these soils, fertilizers, and additives. The benefits of good soil will directly reflect in your harvest, and to enrich soil you have, or build a new soil takes some understanding of the ingredients. Here are some of the components that make a great soil: pH, EC (salinity), cation exchange capacity (ability to hold nutrients), air flow, moisture retention, and drainage. Amendments can benefit the soil in different ways and are usually composed of organic or inorganic material.

Organic vs. Inorganic

The terms Organic and Inorganic might be confusing when referring to soil amendments but let’s discuss what they mean and the role they play. Inorganic, in this context, should be seen as minerals added to help the soil texture, but are generally inert or contain little to no nutrient value. Some examples of inorganic materials are lime, vermiculite, perlite, pea gravel, and sand which are used to control the airflow, drainage, or water retention. Organic, in this context, is categorized as anything derived from a living or natural resource. Adding organic matter feeds the microorganisms who break down the organic material into nutrients that feed the plants. A few examples of organic materials include manure, compost, peat, worm castings, bone meal, blood meal, and bat or bird guano. These organic, and inorganics will be what you use to condition your soil while some might be used as fertilizers. The difference between fertilizers and a soil conditioner should also be clarified; as well as why a conditioner is needed.

Conditioner, Grow, Rinse, Repeat

The term soil conditioner should be synonymous with soil amendments as the two are both used to regenerate or improve the soil over time, so it might be used to grow again. Examples of common soil conditioners are peat moss, coco coir, worm castings and bat guano. We are going to explore both worm farming and bat guano sourcing but I want to explore a common conditioner, coco coir. The forms coco can take are numerous but the fibrous coir is what is usually sold in hydroponic shops. Coir is preferred over something like peat moss for its nutrient and water retention properties. When mixed into soil, the mix can determine traits such as air flow, water or nutrient retention, and drainage. Coir is not compatible with all plants due to its pH ranging from 5.5 to 6.5. Coir is also susceptible to the common greenhouse fungus Leucocoprinus and other pathogenic fungi. It is a great conditioner that I mix at a 60/40 ratio for my own plants, and it is commonly used in hydroponics as a medium. A soil conditioner can also be a fertilizer such as worm castings and bat or bird guano.

Vermiculture, or Yeah, I got Worms!

Vermiculture is the science of worm farming, and composting using worms is known as vermicomposting. Vermicompost is any organic waste broken down by worms in which the process produces valuable worm castings. These are a nitrogen rich natural fertilizer produced by the worm’s gut, basically worm poop that contains active beneficial bacteria and enzymes. The digestion process breaks down the compost and homogenizes the material with sugars, mucus, microbial organisms, as well as excretory fluids like urea. As the compost digests, digestive bacteria will continue to break it down until it is mineralized, stabilized, and excreted by the worms. The contents of compost the worms are fed can make the nutrient contents vary. Worm castings generally have an N-P-K ratio of 3:1:1. The nutrients castings contain are also soluble in water and uptake easily by plants. Worm castings offer the additional advantage that they will not cause nutrient burn to plants.

So let’s talk about how-to vermicomposting, starting with the worms you need to get, being either Red Wigglers or Blue Worms. The worms will be put in a container with a bedding 8 inches deep made of shredded paper, green clippings, and coco coir. The bedding must be kept moist to keep the worms from drying out. The worms are then fed kitchen waste such as vegetables, fruit, bread, grains, tea, coffee, crushed egg shells, and other non-greasy food waste, as well as paper towels, or napkins. Be careful to feed only limited amounts of citrus and pineapple due to the acidity. Material to avoid composting includes meats, fish, greasy or oily foods, dairy, papaya seeds, twigs, branches and animal excrement. The timeframe for gathering worm castings is 3-4 months, with months 5-6 having the most amount of mature castings which will smell earthy when ready to harvest. After harvest, the vermicompost should be kept in a cool dark place for 8-10 weeks making sure to keep it moist and well ventilated. The curing process will further break down organic matter for better texture as well as nutritional availability.

Talkin’ Guano

Worm excrement is not the only valuable excrement for your soil, because bats and birds have plenty to offer. Guano is a carbon and nitrogen rich natural fertilizer that also contains micronutrients as well as beneficial microbes that are easily taken up by the plant. Guano has been used by many cultures around the world in horticulture to increase fertility and improve overall soil health. The age of the guano can vary but is commonly found fresh, semi-fossilized (semi-dried), and fossilized (aged and dried) with the nutritional availability being highest when the guano is fully fossilized. The pH, nutritional value, and overall effectiveness can depend on the bat’s diet.

  1. High carbon guano is sourced from fruit-eating bats

  2. High phosphorus guano is sourced from blood-eating bats

  3. High nitrogen guano is sourced from insect-eating bats

Bat guano is a powerful tool for the cannabis grower, but take caution as it is strong enough to cause nitrogen burn in your plants. A benefit is it can be used in small amounts to condition soil, with a common mixture ratio being 1 part guano to 20 parts soil. Always use caution when handling any guano, if dry make sure to wet, and always ensure the guano is sourced responsibly. Bird guano has been mentioned, with brands like Agromar Seaweed Solutions offering an organic sea-bird guano based liquid fertilizer. The sea-bird diet of fish carries high nutritional value and can be an awesome alternative to salt based nutrients or synthetics.

Meal to Feast

Meal is not something you would eat, but rather a powdered animal by-product that has high amounts of nutrients based on what the meal is derived from. The three main kinds of meal are Blood, Feather, and Bone, each of which has its own unique properties and benefits.

Blood Meal – A high nitrogen powder made from dried blood and known as one of the most nitrogen-rich soil amendments. Blood meal contains a high amount of iron from the hemoglobin in the blood, which is an added benefit to plants that might be suffering from iron deficiency. Blood meal can deter pests such as rabbits, and is acidic in nature meaning soil pH should be monitored prior to planting. It is highly water soluble so it can be added to established plants as well, feeding plants for 6 to 8 weeks after.

Feather Meal – Another nitrogen-rich meal that is made by heating and grinding poultry feathers in a pressurized system. Feather meal is not as water soluble as blood meal so it will release over time as its nutrients are less accessible to plants. This makes feather meal a better long term amendment while blood meal is best used to remedy deficiencies quickly. Both blood and feather meal can be added to compost to boost microorganisms which will speed up the decomposition of carbon-rich compost.

Bone Meal – Bone meal is a phosphorus rich amendment made from animal or fish bones, which are ground into course and fine powders then mixed. Bone meal is a slow-release amendment that also adds proteins and calcium to the soil The finer the powder, the quicker it is absorbed by the plants and is a preferred alternative to Rock Phosphate because Bone Meal is easier to obtain, spread, as well as a higher nutritional content Bone meal contains small amounts of nitrogen, and can be used to balance soils that are nitrogen-rich. Soil with a pH of 7.0 or above will need to be corrected and lowered to under 7.0 prior to adding bone meal to prevent phosphorus lockout.

These basics about amending soil could have you making your own worm casting and looking for the good guano. Continue to do your research and explore the market for your preferred castings, guano, and meals. I will be prepping and amending old soil for use next year, and starting now is the best option knowing what I do. I will be continuing my outdoor flowering, while also vegging my sprouts which include seeds from @bz_selects. Make sure you’re following along by downloading the Cannabis Cactus App or see the full grow series at!


See the whole cultivation series to keep reading and learning.



Adrian Ryan was born in New Mexico and attended school since elementary in Arizona, his time growing up split between the two states. He hopes to work towards recreational cannabis, enjoys reading, writing, film, music, and also writing music.

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