How to choose the best soil for cannabis
Growing your own cannabis in soil is regarded by many as one of the easiest ways to produce high quality crops of delicious tasting buds. But what is the best soil for cannabis indoor growers? What about the best type of soil for outdoor cannabis? The best soil for cannabis combines excellent nutrition and good water retaining properties along with good drainage and an optimum pH.
What are the main traits of the best soil for cannabis?
The best soil for growing cannabis has several important functions to perform in order to allow healthy growth of the cannabis plant and the roots. There is a huge range of options from cheap supermarket soil to expensively blended specialist soils. Not all of these are ideal for growing cannabis. Here are some of the most important features for anyone seeking the best soil for cannabis growing:
Cannabis doesn't grow well in heavily compacted, dense soils. The best soil mix for cannabis tends to be light and airy. This allows good levels of root oxygenation, especially when combined with air-pots or porous fabric root sacks. Healthy cannabis roots will thrive in a light, aerated soil.
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A perfect soil mix for cannabis allows good drainage. Waterlogged soil results in poor root health and subsequent slow growth. If you water your plants and notice surface water forming in pools it is an indication that your soil may have poor drainage.
The best soil for cannabis has good drainage qualities but at the same time it is able to retain some moisture for the roots to absorb.
The best ph for cannabis in soil around 6. Some growers ask ‘how to test soil ph for cannabis?’ You can buy specialist kits which measure soil pH, though many soil growers have never worried about testing pH. To some extent soil is self-buffering, meaning that soil growers need not worry about e.g. pH-adjusting their nutrients in the way that many hydroponic growers have to. Using a larger plant container with more grow medium enlarges the buffer zone and is the preferred approach by many soil-using cannabis growers.
Most soils contain a reasonable level of nutrients. These eventually become depleted, requiring the grower to use perhaps a bloom nutrient as the plant flowers. Nitrogen (N), Potassium (K) and Phosphorus (P) are the main nutrients, but there are plenty of other important trace nutrients which are also required.
Some growers like to avoid having to feed a bloom nutrient. Instead they try to make the best organic soil for cannabis which can feed the plant for the bulk of it’s life.
This can be done with slow release organic nutrients from companies such as BioTabs. Simply mix the slow release organic nutrients into your soil mix. One tip is to use a large initial soil container (e.g. 50 litres or more). With such a large reserve of nutrients in a large container of soil you may be able to avoid the worry of bloom nutrients for much (or even all) of your grow.
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Organic soil vs soil mix
A good organic soil is often produced with generous levels of compost, peat and slow release nutrients which are broken down in the soil by beneficial bacteria. Some of these specialist soil can cost upwards of €/£/$ 50 per 50l bag and are said to contain sufficient nutrition for (almost) the entire grow.
The best soil mix for cannabis is often produced by blending several starting ingredients. The ingredients may include additives that are proven to be useful, such as bat guano, worm castings, dolomite limestone (contains Calcium & Magnesium), coco fibre, mycorrhizal bacteria as well as a high grade nutrient-rich soil/compost.
Many growers have found good results with peat based soils which don't contain wood products. The absence of wood minimises potential problems later on with fungus gnats which thrive in a warm indoor grow room.
Lightmix is a blended soil type which is often used in the cannabis growing community. It contains a mixture of ingredients together with added perlite to make the medium more aerated. It also contains a small amount of nutrients, sufficient for the first weeks. Lightmix soil preparations are a good starting point for inexperienced growers.
The best soil for cannabis seeds and seedlings
Note that the best potting soil for cannabis seedlings and seeds is often a very light mix with low nutrient levels. Young cannabis plants and roots are easily burnt by soil which contains too many nutrients. The best soil for seedlings allows rapid root growth in the light, aerated soil. For young seedlings, nutrition is not as important as it is for mature plants in full bloom. In fact, a light mix with few nutrients is great for seeds and seedlings. Special soil types optimised for seedlings are available, such as Terra Seed Mix from Canna.
Photoperiod vs autoflowering cannabis soil
A good quality cannabis soil will give equally impressive results whether you are growing autoflower seeds or photoperiod feminised seeds. Don't worry about making or purchasing different soil types. The cannabis roots have to absorb the same minerals and nutrients. There is simply no need to source different soils for your autoflower seeds and your feminised seeds. The best cannabis soils work well for both.
Best indoor vs outdoor soil for cannabis
Indoor cannabis growers are spoilt for choice when it comes to soil options. Many of the top brands do a great job. Some indoor growers are reluctant to change from their preferred soil choice once they feel settled with a particular soil recipe which works well for them. As well as trying to grow in the best soil for cannabis, indoor growers also try to fine-tune and improve their grow room conditions.
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Many outdoor cannabis growers simply use the existing outdoor soil. Sometimes this can be supplemented with well-rotted manure and other additives. Experienced outdoor growers will test the soil with specialist test kits and amend the soil accordingly. If the outdoor soil is simply too low in nutrients/quality (e.g. too sandy) then it can be supplemented by high quality soil form the grow shop. Remember cannabis has been growing outdoors without human intervention for hundreds of thousands of years. Cannabis can grow well in many outdoor soil types.
Outdoor growers can grow their plants in the ground or in containers. When growing in containers avoid dark coloured/black containers which can get very hot in direct sunlight and ‘cook’ the root ball. This can slow growth rates or even kill the plant.
When growing cannabis outdoors in hot, dry regions some growers add water absorbing crystals to the soil. These are water retaining polymers (as used in babies nappies) which can greatly increase the water retention properties of your soil.
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Store-bought vs homemade cannabis soil
Many less experienced growers find it convenient to buy ready-made soil from their grow store. The more professional ‘living soil’ blends can be very expensive. That’s why some growers like to save some money and create their own soil blend themselves.
Note that there is not a single, definitive ‘best soil recipe for cannabis’. Cannabis grows well under a wide range of conditions and substrates. But if you want to know how to make your own soil for cannabis you may find the following recipe a good starting point. But remember you can vary the ratio of ingredients and even add your own supplements until you reach a blend that works well for you.
Basic cannabis soil recipe
Your choice of ingredients is quite wide. You can lighten the soil mix with coco coir, perlite, vermiculite or even sphagnum moss according to your preferences. Here is a suggested mix.
• 1 part coco fibre
• 1 part perlite
• 2 parts compost
• 1 cup of worm castings
Note. Other popular additives include small amounts of blood meal, dolomite lime, fish meal, bat guano, peat, bone meal etc. Mycorrhizal and other beneficial bacteria are also great at breaking down the soil and gradually releasing more nutrients. They are highly recommended to create a healthy ‘living’ soil.
Steps to follow:
• Sieve the compost to remove/break down any large lumps
• Place the sieved compost in a large mixing bucket and add the other ingredients
• Using your hands, ensure that all the ingredients are thoroughly mixed together.
Remember you can modify your recipe as you gain experience. But not everyone has the time to manually prepare and fine-tune their soil mixtures. For some people it’s easier to buy a proven brand of soil mix from the grow shop. For some growers the best cannabis soils are simply the easiest grow medium in which to produce the finest tasting organic cannabis.