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Traditional Methods – Soil

why use soil for your cannabis plants?

For beginner growers, soil is often the first choice to grow cannabis plants. It’s conventional, familiar (particularly if you already love gardening), fairly easy to create your own soil mix and it’s also cheaper than other options. Soil is a great natural and easy option for those starting out, but you do need to make sure you are using the right soil for your plant. 

what is a good soil?

Soil is made up of minerals, organic matter, biological organisms, water and air. The air in soil is more like a gas and takes up around 25% of the soil. The organic matter, such as animal particles and microorganisms, only take up a small percent (about 5%) of the soil but can make a huge difference in the quality of it.

Soil for cannabis plants should be a nice dark colour, rich, loose in texture, it should have good moisture retention but also drain well (when water is poured on it, the soil should drain it our within a few seconds). Water retention is needed so the roots do not dry out but it needs to drain well, to prevent over-watering. 

trowel with soil

types of soil

The minerals in soil are made up of clay, sand, silt or loamy.

Clay is great for soil as it contains many nutrients such as potassium, magnesium, iron, and calcium. Soil should not have too much clay however, as it can be heavy, making it difficult to break up and work with. It contains higher pH levels and has a smaller granule size.

Sand does not contain any nutrients and too much of it can be a problem. The grains are larger and contains fairly low pH levels.  In small doses, it’s useful for drainage and turning up the soil.

Silt is a mixture of sand and minerals but does not really contain many nutrients. It can be easily compacted and therefore does not drain so well.

Loamy is a combination of clay, sand, and silt but with extra organic compounds. This is a good soil for cannabis but can be expensive. It has a neutral pH level, has lots of oxygen and nutrients and is good at both drainage and water retention.

organic matter

Organic matter is made from plants or animals that are either alive or have been decomposed. It will make quality soil, which in turn will create a quality plant. Examples of good organic matter for your soil are compost, manure, fish, kelp, coco coir, blood meal, bat guano and worm castings. Potting soil may be good for other plants, but not so much in cannabis, as it does not drain well and you will need to add extra nutrients. If you buy soil with nutrients already in it, then they will only last around 3 to 4 weeks, so you will have to change the soil before the flowing stage begins.

Remember, the type of soil you will need can differ with which cannabis type you are growing, the climate and whether you are growing indoor or outdoors. Auto flower types prefer a lighter soil with fewer nutrients. You should also consider the pH level (acidic or alkaline percentage) of your soil. A pH level of around 5.8 to 6.3 is good for growing cannabis. 

how to improve your soil quality

If you want to make your own soil, rather than buying one with the nutrients already in, then there are a few things you can do to increase it’s quality. By adding various organic matter and nutrients you can create the perfect soil for your plant.

Perlite: This is one of the most popular ingredients for soil enhancement. It’s made from small, white rocks, and adds oxygen which helps to air out your soil, as well as improving drainage. Try adding around 10 to 15 % of perlite to your soil for the best outcome.

Vermiculite: This is similar to perlite; in that it will make your soil lighter if you have really heavy soil. Instead of helping with drainage like perlite, it will help your soil with water retention. Around 10% is a good amount to add to compliment the perlite.

Worm Castings: These can add a great nutritional enrichment to your soil, as they contain lots of microorganisms that will help your plant grow. Around 25 to 30% of the work castings will help with water retention and drainage, giving your soil a nice texture.

Coco coir: This is created from coconut husks. This will also lighten your soil and help with retaining water. These light fibres provide excellent water retention and can lighten compact soils. 

garden spade in soil

best soil for outdoors

Potassium (K), nitrogen (N), and phosphorus (P) are the three main nutrients that cannabis plants need. Using a store bought fertiliser, you can manage the nutrient levels of your plants throughout the growing season.

To grow outdoors you need a good, healthy soil. It should form a nice ball in your hands when you squeeze it but then be able to break away in chunks, once you let go. If you are planting straight into the ground, then you will need to test the soil for it’s pH levels and quality. If putting your plant into an outdoor pot, you will need to be able to maintain it’s nutrients, as it cannot rely on any other soil around it. This does allow you to have better control over what nutrients the plant receives. 

shop bought soils

Buying pre-made soil from the shop can be a great idea for those starting out on their cannabis growing journey. Keep in mind that you will need different soil types for indoor and outdoor growing. You should avoid buying soil that has extended release nutrients, which can ruin cannabis crops.

When buying soil for seedlings, look for simple potting soils have fewer nutrients, as the young seedling plants do not like a super rich soil. Once your plant starts the flowering stage, you can start adding more nutrients.