Growing great weed is not that difficult when you start with a fertile living soil.

Unfortunately, quality organic potting soils are not always available at the big box store.

Amazon will drop a bag at your door, but shipping plastic bags of soil is expensive, and the product might be dead on arrival due to improper storage.

You can do better if you are willing to put in a little bit of work.

This article will teach you everything you need to know to mix your own organic soil.  

My not-secret-anymore living soil recipe is included below.

Organic Potting Soil

Organic potting soils are designed for high-intensity cultivation in containers.

The best organic soils are nutrient dense, with a diverse microbial community, and a structure that supports rapid air and water exchange in the root zone.

When organic nutrients are in balance, plants can select from a diversity of elements to fuel their growth. This balanced fertility is provided by beneficial soil microorganisms breaking down organic residues to make them plant available.

In most cases, the best soil for cannabis is made from locally sourced inputs.

Super Soil

Super Soil is the legacy grower’s answer to the widespread availability of low quality potting soil.

A commercial potting mix was used as a base and amended with various inputs. The idea was to make a very fertile mix that would support a full cycle plant without additional feeding. This approach can work in some cases, but you can make a better soil for less money by skipping the commercial mix.

Plants respond better to a well balanced soil that is not too hot, and will benefit from supplemental feeding. Dry fert mixes can be applied to supply slow release nutrients, and liquid fertilizers can provide nutrients for immediate uptake.

Organic Compost

High-quality compost is the beating heart of an organic fertility program.

Compost provides a diversity of biology and plant available nutrients. Production of quality compost requires blending organic residues at appropriate ratios and careful management of cultural conditions to promote beneficial microbes.

I am fortunate to live on the West Coast, with access to well-balanced compost containing salmon and fir bark fines. Manure based composts are also sometimes commercially available.  In my area, municipal composting systems generally do not produce the input quality we are looking for.

Even if you buy your compost in a bag, it is likely to be higher quality if it is sourced from your geographic region.

Nutrient Analysis

Commercial compost producers can often provide a nutrient analysis of their product. 

This document can be complex to interpret.

The ratios between various nutrients are more important than the actual values, and each soil lab has its own protocols for sample prep and extraction. There are a couple of important numbers to check on a compost analysis that can tell you a lot about its quality.

Carbon to Nitrogen ratio

The Ratio between these critical elements affects Nitrogen availability. The C:N ratio should be below 25 in most cases, and compost that tests above 35 should be avoided.

Electrical Conductivity

EC is a measure of nutrient salts that are available in the soil water. Most nutrient dense composts should have an EC above 4.

Soil Structure

Potting soils are built on fibrous grow media to create an aerobic soil structure that benefits root and microbe health. The soil environment influences microbial communities as conditions will favor reproduction for some species, and dormancy for others. Different grow media have various chemical and physical features that influence the mix design.

Peat Moss

Sphagnum Peat Moss is the most common grow medium used in potting soils. 

This product is the result of slow decomposition of organic materials within anaerobic peat bogs. 

Peat has excellent water holding and drainage capacity. It is also acidic and can become hydrophobic or hard to re-wet when it dries out.  There are environmental concerns about this input due to its slow formation, and release of carbon during peat mining activities.

Aeration inputs

Soil amendments are often incorporated into potting soils for air entrainment.

• Perlite is an inert material that is created through heat treatment of volcanic glass.

• Pumice is a mined volcanic aggregate that naturally entrains air and water within a porous structure.

• Rice Hulls will break down relatively quickly, losing aeration properties and providing silica for plant uptake.

Soil Fertility

In addition to compost, a variety of soil amendments are used to build fertile potting mixes. These inputs provide essential macro and micronutrients to the soil food web, and benefit soil chemistry and structure.

Mineral Inputs

Naturally occurring mineral compounds are important inputs for living soils.

Products referred to as Lime contain Calcium and other minerals. Lime is an important component of any potting soil as it counteracts the acidity of other inputs.

The most common liming agents used for growing plants are agricultural lime, which is primarily calcium carbonate, and dolomite lime which contains Calcium and Magnesium. The type of lime that is used depends on the characteristics of other soil components. Potting mixes based on coco coir uptake lots of magnesium, and exchange it for potassium during the grow cycle.

Other mineral sources that can be used to supply important trace elements are glacial rock dust, Azomite, and greensand.  Some of these mineral inputs require a substantial amount of time to break down and become available for plant uptake.

Protein Meals

Protein meals are commonly used as supplementary livestock feed and are widely available at feed and tack stores.

Protein meals include both plant and animal-based products, and availability will vary by region. These inputs are dried and milled to increase storage life, and bioavailability.

• Blood Meal is Nitrogen dense and breaks down quickly in the soil. 

• Feather meal is a great source for slow-release Nitrogen.

• Fishbone Meal provides Phosphorous to promote root and flower formation.

• Kelp meal is a rich source of Potassium, micronutrients, and plant growth factors. 

• Alfalfa meal is a balanced input containing triacontanol, a hormone that promotes flower development. 

• Insect Frass (manure) contains moderate Nitrogen, and chitin, a compound that aids plant defenses.

• Crustacean meal contains slow release Calcium, Phosphorous, Nitrogen.

Organic Fertilizer

You can make a balanced, slow release, organic fertilizer by combining protein meals with different nutrient qualities.

For soil mixing we are looking for a balanced blend with similar levels of Nitrogen, Phosphorous, and Potassium (N-P-K). This Base Mix can be used in the organic soil recipe below:

Mixing Dry Ferts

There are nine parts in this mix. If you are just mixing a few barrows of living soil, use one cup to measure each part in the base mix recipe.

I usually use a one liter scoop to measure protein meals for larger nutrient blends.

Wear a dust mask when mixing any particulate inputs, this stuff is not good for your lungs.

An easy way to mix dry inputs is to pour them from one bucket into another and repeat until fully blended.

This base mix will store well if kept dry, so don’t worry if you mix more than you need for one soil session.

Organic fertilizer blends are widely available to purchase. Various products are available, and will work with this soil recipe as long as the N-P-K Values are relatively balanced (4-4-4)

Living Soil Recipe

This recipe is for one wheelbarrow, or about 2 cubic feet of living soil.

You will need a wheelbarrow, a spade shovel, a 5-gallon bucket, a measuring cup, and the following ingredients.

Mixing soil is like baking a cake. Measuring carefully, and following directions is important to ensure a fluffy and delicious result.

First you want to add the peat and other dry ingredients to the barrow and mix thoroughly. This ensures that soil amendments will be distributed evenly throughout the mix.

Now you can add the compost and coir to the mix and blend again.

Add a bit of water to the mix if necessary to hydrate until the soil is plastic enough to form a ball, with no water escaping when squeezed.

Soil Mineralization

After all of that mixing, your living soil deserves a rest.

Making your soil mix a week or two before you need it will allow the microbes to get to work. 

Storing soil in an aerobic environment, at room temperature, will allow nutrients to mineralize and become plant available. Soil will sometimes heat up slightly during early mineralization.

White mycelial growth on the soil surface is a positive indicator of fertility.

You now have enough information to be dangerous. If you want to make the most of your amazing soil, you should check out the other articles in the Grow Basics series.

Tractor Mixing

If you plan on growing lots of plants, hand mixing in a wheelbarrow is not going to be fun. Drum mortar mixers, or large soil mixers can work well, but a tractor is a better tool for mixing large amounts of soil.

If you are mixing living soil at commercial scale, you should hire a soil expert like me to help you develop your organic fertility program. Reach out with the form below to start a conversation.