There’s lots of information online about soil recipes and amendments, so we put together a list of the basics. 

The importance of nutrition and bioavailability

The health of your soil and the quality of your harvest depends on the balance of organic and inorganic matter. Organic matter is broken down by microorganisms to be released as important nutrients that feed your plant. Inorganic matter serves to increase the quality of your soil texture with improved aeration, water retention and drainage.

Using basic gardening soils may be an average start at best, but these soils are lower quality and don’t provide the full spectrum of nutrients that cannabis needs. Cheap potting soil typically has excessive lumber industry byproducts (mulched bark) and doesn’t drain well, resulting in waterlogged roots that stop your cannabis from thriving. 

Indoor cannabis growers especially benefit from adding soil amendments since they don’t have the natural processes that build up organic matter in a garden. By regularly replenishing nutrients, they’ll see results, like a larger yield and improved potency.

NPK- the most important nutrients

Growers use NPK ratios when building or purchasing soil and fertilizers. NPK stands for nitrogen, phosphorus, and potassium, which are the 3 most important nutrients for your cannabis plant’s health. Each growth stage in your plant’s life cycle will need different proportions of NPK, so you’ll need to monitor and supplement levels as needed. In general:

  •     Seedlings need more nitrogen and less phosphorus
  •     Vegetative plants need higher nitrogen and even lower phosphorus and potassium
  •     Flowering plants need equal parts nitrogen and phosphorus with lower potassium

Nitrogen is an important component of chlorophyll  which is needed for photosynthesis. Without the energy created by nitrogen, the plant can’t feed itself and it’s growth will be stunted. Phosphorus is important for developing strong roots and aids in many functions. Lastly, Potassium strengthens your plant by helping regulate the movement of water which enables your cannabis plant to stand upright and prevents wilting. Only small amounts of potassium are needed compared to nitrogen and phosphorus.

In addition to NPK, healthy soil will also need trace nutrients like calcium, magnesium, sulfur, iron, zinc, copper, and manganese.

Choosing your base soil

Before choosing which amendments you want to include, you need to decide on your base.

Here are a few of the most popular components: 

  •     Coco Coir- comes from the fibrous layer in between the hard outer coat and the internal coat of coconuts. Coir is very water resistant as well as is high in potassium and sodium, which prevent nutrient deficiencies in plants
  •     Peat Moss– a form of Sphagnum moss after it has been dried and decayed. Mix this with your soil to regulate air around the roots and increase moisture and nutrient retention
  •     Compost– an excellent source of potassium for your cannabis plant. Include food scraps but avoid meat, dairy, fish, and twigs or branches. When you have completed a harvest, add in the stalks and roots of your harvested plants.
  •     Perlite or vermiculite– effective additives that support air flow. Both of these inorganic materials are lightweight and do a terrific job of aerating the soil and warding off root rot.

Your soil amendments cheat sheet

We put together a list of the most popular and effective amendments to add to your soil. Take a look at our cheat sheet to learn more about how they work and what benefits they deliver to your plants.

Worm castings

  •     Created through vermicomposting and is essentially, worm poop
  •     Works well in compost created with scraps of veggies, fruit, grains, tea, coffee, crushed egg shells and non-greasy food waste
  •     Full of active bacteria, organic matter, enzymes, and worm cocoons
  •     Promotes earlier plant emergence and more consistent root growth
  •     Helps deliver nourishment and regulates pH levels
  •     Safe to use around children and pets

Guano

  •     Bat (and sometimes bird) guano comes from carbon and nitrogen rich bat feces
  •     Contains micronutrient minerals and microbes that are easy for the plant to consume
  •     Especially effective when combined with worm castings
  •     Enriches soil fertility and improves texture
  •     A little goes a long way, making it more efficient than other types of manure
  •     Doesn’t cause nutrient burn to plants

Neem cake

  •     Comes from the dried residue after oil has been pressed from the seeds of neem trees
  •     Boasts a solid NPK profile with many trace elements
  •     Improves the conditions for nitrification and prevents root rot
  •     Includes an active agent called Azadiractin, which provides defense against molds, nematodes, and leaf eating insects. Instead of killing pests directly, it triggers a stop-eating response so the pests starve to death
  •     Effective against aphids, beetles, cockroaches, flies, fungi, mosquitos, moths, snails, spider mites, and thrip

Karanja cake

  •     Comes from the dried residue after oil has been pressed from crushed Karanja seeds
  •     Like Neem, Karanja is naturally rich in NPK and works as an excellent organic fertilizer
  •     Known to increase earthworm populations where it has been added to the soil
  •     Has a milder aroma than neem oil; it smells and tastes nutty

Crab meal

  •     A popular fertilizer for as long as people have lived by the sea
  •     Composed of “chitin” which makes up the crab exoskeleton and is a strong deterrent to fungus gnats
  •     Works in conjunction with cannabis, which creates an enzyme that breaks down chitin and stimulates the immune system
  •     Includes very high concentrations of nitrogen, phosphorus, magnesium, and calcium
  •     Results in increased terpene or cannabinoid synthesis

Oyster shell

  •     Made of ground oyster shells and supplied through oyster farming which is a very sustainable aquaculture
  •     Provides calcium and micronutrients, regulates pH and improves nutrient uptake
  •     Provides an ecosystem for soil microbes that break down organic matter and replenish nutrients
  •     Keeps away moles, voles, snails, slugs and more

Kelp

  •     Made from dried seaweed
  •     Adds potassium to soil, as well as over 60 essential nutrients, elements and minerals that support soil microbes
  •     Increases sweetness, boosts flavor and enhances the color of your crop

Mycorrhizae

  •     A must-have beneficial fungi
  •     Supports the roots and helps plants absorb water and nutrients
  •     Solubilizes phosphorus and other nutrients, making it easier for the plant to take up food
  •     Protects roots from damage by harmful microbes

Adding compost teas

Some growers choose to use compost teas during vegetative and flowering stages to give plants a potent shot of nutrients. These cocktails of fungi, bacteria, protozoa and nematodes work together to improve your plant’s overall health. Teas can reduce the presence of weeds and pests, help plants fend off diseases, and improve water retention.

Teas can also safeguard cannabis from pathogens that can harm or kill it by strengthening their immune systems. It’s best to wait at least a few weeks or a month between applications. Common ingredients in compost tea are compost, kelp, molasses, worm castings and fish hydrolysate.

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