Growing cannabis isn’t as simple as growing the average houseplant. It is true that it can be grown in a variety of soils, however, if you want your cannabis plants to thrive then you need to make sure they have the perfect environment, and that includes the perfect soil. But precisely what is it that makes the best soil for growing cannabis? And how can you amend your garden soil so that your cannabis plants thrive? Let’s dive in.
What makes a good soil or compost for growing cannabis?
You probably could just plant a cannabis seedling in your garden soil and chances it would grow. However, if you want to grow a healthy, huge yielding, bud filled plant then you need to make sure the soil is perfect. The best soil for cannabis plants need to provide the following things….
Soil density is key to plant health
Young cannabis plants are delicate, if you want them to thrive you must take proper care of them while they are growing. If your soil is too compact (a common issue with clayey soils) the plant roots will struggle to grow. A good soil should be relatively loose and airy so that the roots can easily grow.
Amendments such as perlite and vermiculite loosen the soil and create air pockets making it easier for roots to expand while increasing oxygen intake and they can also assist with drainage and water retention.
A great soil should provide nutrients
Nutrients are vital for optimum growth and all round plant health. Different types of soil contain varying levels of nutrients. Amended or composted living soils generally contain more nutrients which is very useful for aiding growth, particularly in a plant’s early life before you begin to add additional nutrients.
Amended and composted soils, also known as living soils, contain micro-organisms that live in the soil. This replicates soil that is found in nature closely and provides a plant with a healthy balance of the right nutrients. Nowadays it is easy to find good living soil that comes already pH balanced and contains all of the nutrients required for cannabis to flourish.
You can also make your own living soils using compost, bat guano and worm castings.
A good soil should have good water retention and drainage
Although these may seem like opposites, it’s about finding a happy medium between the two. The ideal soil for cannabis should offer good enough water retention that it doesn’t dry out too quickly and good enough drainage so that water drains through at a gradual pace and does not sit and become stale.
If you are making your own soil mixture it is easy to create a soil that meets all of these criteria. However, if you plan to grow your cannabis plants outdoors using the soil that already exists then you may need to add a few amendments to improve certain aspects of it.
What are the different types of soil and amendments?
Soil and compost
Soil and compost are the two most common mediums to use for growing cannabis, because they are easy to use, natural and readily available to almost everyone. Many beginners often make the mistake of assuming they can just use some soil from their backyard to grow cannabis in. In most circumstances this will work however there is a little more to it than that.
Silty soil
Silty soil contains lots of natural minerals and nutrients which makes them great for growing cannabis, however drainage is not the best, although This can easily be amended by adding something such as perlite.
Loamy soil
Loam is a combination of silt, sand and clay and comes in different densities depending on which ingredients make up the biggest portion. Loamy soil provides excellent water retention and drainage as well as being rich in nutrients which makes it great for cannabis.
Clayey soil
Soil rich in clay is usually full of naturally occurring minerals, however it is incredibly dense and heavy and can be difficult to work with. Because of its density it usually has poor drainage and the roots of a plant can struggle to grow.
Sandy Soil
Sandy soil is highly course and doesn’t have very good water retention. However it does have good drainage and can easily be amended to work well with cannabis.
Bottom: Loamy soil – Clay soil – Sandy soil
What if my garden soil isn’t suitable?
If you have particularly dry or dense clayey soil in your garden don’t worry, it is difficult to work with but you can still grow cannabis by amending it with other substrates.
If you have soil that you think is not suitable for growing weed, first dig up a patch of the soil about 2 feet deep. Then either mix in with or replace it with our homemade soil mixture that we will explain how to make below.
If you live in a hot dry climate and you’re worried about water retention in your soil you should ideally water more often. However, if regular watering is an issue you should try adding some polymer crystals to the bottom of your pots. These provide excellent water retention and will give your roots something to drink even in drier conditions.
You should also consider using air pots. Air pots will prevent your roots from being baked by keeping the soil cool during hot climates.
What are the best cannabis soil amendments?
Compost
Probably the cheapest and easiest to come by, if you don’t have your own compost heap at home you can easily pick a few bags up from your local gardening center for next to nothing. Compost is made up of decomposed plant matter and provides a regular supply of nutrients to your cannabis plants. The make-up of composts can vary however so be sure to check the pH falls within the 5.8 – 6.3 range before you used it.
Worm castings
Worm castings provide plenty of slow release nutrients for cannabis plants, they are 100% organic and offer excellent drainage, water retention and aeration.
Bat guano
Made of bat droppings, bat guano basically bat manure and is rich in nutrients. It provides decent drainage and water retention and can actually be used to grow cannabis without anything else. Bat guano is so nutritious that you can grow cannabis in it without the need to supply any extra nutrients.
Perlite
Perlite is a manmade substance made from volcanic grass. It looks like tiny little white gravel stones. Their main use is that they are incredibly light and airy and are great for improving highly dense soils. If you have dense soil, try adding 15% perlite to it. This will create pockets of air which will both improve drainage and loosen the soil which will help roots to grow.
Vermiculite
Similar to perlite, vermiculite is great for improving the density of soils, but it can also aid with water retention. Perlite and vermiculite can work great together in hard or dense soils to improve the airiness, drainage and water retention.
Peat Moss
Peat moss is a mixture of different species of moss. It is full of beneficial nutrients but has poor water retention. Make sure you soak any peat moss in water for 1-2 weeks prior to adding it to your soil mix to improve its water retention.
Clay pebbles
Clay pebbles are most often used when growing cannabis in hydroponics. However they can also be added to soil to improve drainage, airiness and overall structure. Clay pebbles contain no nutrients at all however they can be added to the bottom of a soil bed or pot to create a pocket of air. This allows water to drain effectively and creates plenty of room for roots to expand into.
How to make the perfect DIY cannabis soil
Rather than trying to find the perfect soil mixture why not try and make your very own DIY soil mix at home? Anyone grower can make their own mixture, regardless of experience level, all you need are 4 components.
- 1-2 Cups worm castings
- 1 Part bat guano
- 1 part coco coir
- 2 Parts compost
- 1 part vermiculite
To make your own soil at home just mix these in the ratios given and you will be left with a soil that is perfect for growing weed.
Before you use it, make sure you test the pH level using a pH meter. The ideal pH for cannabis soil is 5.8 – 6.3. Once you have confirmed this is within the ideal range you can get planting.
One last point, bat guano is great for the cannabis flowering stage so if you have any leftover save this and use it as a soil dressing once you plant reaches the flowering stage. Then when you water your plants the extra nutrients will filter down into the roots of your plants creating a healthy bloom.
Does cannabis have to be grown in soil?
There are lots of different growing mediums for cannabis, so soil is certainly not the only option. The three most popular growing mediums for weed are: soil & compost, soilless mixes or clay pebbles; which are mostly used with hydroponics.
Cannabis plants can thrive using any of these growing mediums, so long as it consistently supplies the roots of the plant with access to water, oxygen, and nutrients.
On that note, the best growing medium for cannabis can be made up of any components as long as they meet these requirements:
- Good drainage and aeration but also retains water well.
- Have a pH around close to the ideal range of 5.8 – 6.2.
- Provide enough nutrients to feed the plant at least until the vegetative stage where you can begin to add your own nutrients.
- Not too dense so as to stop the plant’s roots from expanding.
What are other alternatives to growing in soil?
Growing cannabis in soil is a traditional method, but there are several alternative growing mediums, including:
- Hydroponics: Growing cannabis in a nutrient-rich water solution rather than soil. Hydroponics growers most often use clay pebbles, coco coir or rockwool.
- Aeroponics: A type of hydroponic system where the roots of the plants are misted with a nutrient-rich solution instead of being submerged in water.
- Coco Coir: Using coconut coir as the growing medium instead of soil.
- Rockwool: A popular hydroponic growing medium made from melted basalt rock and chalk.
Each of these methods has its own advantages and disadvantages. Methods such as hydroponics provide a constant supply of nutrients to the roots of a plant and can result in faster growth, higher yields when done correctly.
