What is the best soil for weed plants?

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For those of you who are beginners, a growing medium in the marijuana world is whatever substrate you use to grow your plants in, be it soil, pebbles, rockwool etc. There are lots of different types of cannabis growing mediums all with their advantages and disadvantages, at the end of the day marijuana plants are like any other living thing, as long as they have room to grow and enough oxygen, water and nutrients they will thrive. So what would make the best soil for weed plants to grow?

Growing cannabis in soil

​Growing weed in soil is the most popular method, mainly because it is the easiest to come by and it’s cheap. Many people simply choose to grow using the soil that’s already present in their garden virtually costing them nothing. However, it is important to make sure whatever soil you are using is right for growing marijuana.

What makes a good soil for growing weed?

  • Good soil should contain lots of nutrients
  • Should be loose and airy and provide good drainage.
  • Have a pH between 5.8 – 6.2.
  • Provide good water retention.

A good quality marijuana soil should be loose (non dense) if the soil is too dense then it can often prevent water and oxygen from penetrating into the roots of the plants and also prevent the roots of the plants from expanding. This is often why people when using soil or compost will add small stones into the mix or perlite, this creates little pockets of air and assists with drainage. Keeping the soil nice and airy also allows the plants roots to easily expand. A good mix will have around 20-25% minimum of something like perlite mixed in with it. 

cannabis seedling in pot with soil and coco coir mixture

What is found in a good cannabis soil?

Sandy soil

Its perfectly fine to have sand in soil as it improves drainage, however you should know that it doesn’t hold water well and can cause some nutrients to be washed away too quickly.

Silty soil

Silt is an allrounder as it naturally contains plenty of minerals and nutrients, has great water retention whilst also offering decent drainage. If the soil in your garden is silty it could be ideal for growing cannabis in.

Loamy soil

Loam is a type of soil that is made up of sand, silt and clay. It is usually rich in minerals, offers great water retention and provides excellent drainage for growing cannabis.

Clay soil

Clay soil is rich in nutrients and minerals, however it is incredibly dense and heavy and has poor drainage. If you have lots of clay in your garden soil a good idea would be to dig out a large amount of it and replace it with loamy soil and mix in some perlite to improve the drainage.

What is living soil and is it good for growing weed?

Some soils, called living soils have tiny microorganisms inside them that help to produce the natural minerals and nutrients that a plant needs to survive. Each type of organism bacteria, actinomycetes, fungi, algae and protozoa all provide a unique benefit to using this type of medium such as providing nitrogen.

Because of the natural nutrients in soil you do not usually need to add your own nutrients. All that you need to make sure you do is re-pot into new fresh soil before the plants begin to produce bud. The only downside to using soil is that plants often grow slightly slower, however in my experience the difference is not enough to be a big disadvantage.

How much water do weed plants need daily?

There isn’t an exact answer to how much water your cannabis plants need daily. This is because it really depends upon the size of the plant, the growing medium, size of the pot, and the climate. In hot conditions plants will need watering more, whereas in rainy or humid conditions plants will need watering a lot less, if at all.

For the average indoor cannabis grow a good rule of thumb is to water your plants until you start to see the water draining out of the bottom of the pot, then you can stop. Leave it for 12 hours and feel the surface of the soil, if the surface is still damp don’t water it anymore. If the surface of the soil is dry dig your finger into it about an inch deep, if it feels dry underneath you can give them another water.

watering cannabis plants

Will any soil work for weed?

Cannabis is not a hardy plant and so it will require more care and attention than your average house plant to thrive. What you need to remember is that you aren’t just aiming to keep your cannabis plant alive, you want it to grow big and strong so that it produces plenty of bud for you to smoke. To produce lots of bud the best soil for weed plants must have a good supply of nutrients. Most garden centre soils will contain very few nutrients so you will need to amend them with things such as compost, bat guano or worm castings to make them perfect for your cannabis plants. Store bought soils may not have the right pH levels for cannabis, so you will also need to check the pH of any soil that you buy. For cannabis to thrive the pH needs to be between 5.8 – 6.3. A good soil should also provide good drainage and offer good water retention. If you grow cannabis in your garden, dig a hole about a foot deep first and check the texture of the soil, if it is dense and clay-like you will need to amend the soil to reduce the density and allow better drainage.

Is Coco better than soil for weed?

A common question among first time growers ‘is coco coir better than soil for growing weed?’. The answer isn’t a simple yes or no. You can grow cannabis in coco coir and nothing else, however, coco coir contains no nutrients of its own and therefore it usually only used as a standalone with hydroponics growing where the plant has a constant supply of nutrients.

For less experienced growers it is advisable that you choose something simpler to begin with such as compost, bat guano or worm castings in a mixture with something like perlite. Soils containing this contain plenty of naturally occurring nutrients so that you don’t need use any extra nutrients throughout the grow.

Cannabis growing mediums and amendments

Bat Guano

Bat Guano is basically bat manure. It is an incredibly effective as a fertilizer because it is so nutrient rich. For anybody that wants to grow organically, bat guano provides enough nutrients to supply cannabis plants throughout the vegetative and flowering stages. Bat guano can be added to any soil to enrich it with nutrients, it can also be used as a standalone for growing marijuana.

bat guano is a nutrient rich amendment you can add to make the best soil for weed plants

Worm Castings

Worm castings are an organic fertilizer produce by earthworms. They are another natural soil amendment that works great with cannabis by slowly releasing nutrients to your plants. They are a great addition to cannabis soil because they improve aeration, drainage and water retention.


Compost is cheap and readily available at any garden centre or you can even make your own at home using old vegetables, leaves and twigs. It provides a rich dose of microorganisms giving your cannabis plants a constant supply of nutrients. Compost is made up of lots of decomposed organic materials and is usually more airy than standard soil resulting in improved drainage.

compost can be used to make the best soil for weed plants

Coco Coir

Coco Coir is made from the fibre of coconut husks. It is excellent for improving water retention and aerating more compact soils. It is possible to grow in just coco coir, however it is low in nutrients so you would need to provide additional nutrients to your plants to counter this.


Perlite is mined from a volcanic grass and looks like tiny little white gravel, but they are incredibly lightweight. Perlite is a great addition to heavy or dense soils because it will improve drainage and aeration.


Very similar to perlite, vermiculite are like incredibly little lightweight stones that will help to make your soil lighter. Unlike perlite, vermiculite actually improves water retention. You can effectively use both vermiculite and perlite together adding around 10% of each to you soil mix.

Clay Pebbles

Clay pebbles are most commonly using with hydroponics set ups, however they can also be added to soil. Because of their size clay pebbles are great for adding at the bottom of a pot or garden grow bed where they they will help to improve drainage and prevent water from pooling. They also help aeration which keeps your roots fresh while they are growing.

Peat Moss

Peat moss is another additive that is made up of lots of different species of moss. Peat moss is a little unusual and growers will need to fully prepare it prior to adding to soil. Peat moss has particularly poor water retention and so it will need to be soaked in water first for a couple of weeks before being added. The great thing about using of using peat moss is that it is incredibly rich in beneficial microorganisms.


Rockwool normally comes in cubes. It is a material made from woven basaltic rock that is mostly used with hydroponics growing or for germinating seedlings. Rockwool doesn’t contain any nutrients but since its mostly used with hydroponics that isn’t an issue. It is a lightweight material that offers excellent water retention and provides everything that your plants will need growing hydroponically.

How to make the best soil for weed plants

Making a soil mixture is easy no matter what your experience level. The best soil for weed plants should have plenty of nutrients, good drainage, good water retention and be light and airy so that your roots stay fresh and find it easy to expand. Here is our basic soil recipe that provides everything that a cannabis plant needs to thrive.

Home made soil mix ingredients:

  • 1 Part bat guano – This will provide plenty of nutrients for your plants.
  • 1 part coco coir – Soak your coco coir in warm water first to aid water retention. This will improve water retention.
  • 2 parts compost – Sieve it before adding it to your mixture to remove larger pieces that may not have composted. This will be the bulk of the mixture and provide plenty of nutrients whilst keeping good drainage.
  • 1 part perlite – This will keep your soil nice and light allowing the plants roots to easily expand.

You can play around with this mixture and add or remove certain elements and replace them with others. What you should think about before you begin making a soil mixture is if you want to grow organically or if you are going to be adding nutrients. The mixture above should provide ample nutrients for a cannabis plant from seedling to harvest without any additional nutrients. If you are going nutrient-free just keep in mind that you want the bulk of your soil to made up of a substrate such as bat guano, worm castings or compost. These provide plenty of nutrients, if you were to swap these with ordinary soil, clay pebbles or rock wool you would need to use some form of nutrients to feed your plants.

If you want to add further nutrients to your soil organically, bat guano is well known as an excellent fertilizer. You could add more of this as a top soil as your plant approaches the flowering stage, then just simply water it and let the nutrients filter through.

Always check your pH

Once you have made any soil mixture, don’t just trust that it will be perfect for your cannabis plants, always check the pH. Organic matter like compost can have varying levels of pH especially if it is made at home. Use a pH meter to check your homemade mix the best soil for weed plants should have a pH of 5.8 – 6.3.

How to amend cannabis soils for hot/dry conditions

If you live in a hot dry climate and your garden soil is particularly dry you will need to add some amendments to make it cannabis friendly.

The soil inside a pot can get very hot under the beating sun all day, this can cook the roots of a plant resulting in stunted growth. To keep your roots cool, consider using smart pots or air pots that allow the soil to breathe and keep your roots cool.

In hot conditions your plants are going to require lots of watering. Unless you can make regular trips to water your plants its a good idea to improve the water retention of your soil. Try adding vermiculite and coco coir to soil so that it retains water for longer stopping it from drying out.

Another trick is to use polymer crystals to the soil bed before you plant your cannabis. Polymer crystals are super absorbent and are able to retain water for long periods. So even if your soil dry’s out the roots will still be able to drink the water from the polymer crystals.

cannabis plant growing in dry soil

Soilless growing mixes

Soilless growing mixes are typically made up of perlite peat moss, coco coir and rockwool. The biggest advantage of using mixes like this is that you feed the nutrients to the plant directly using hydroponics meaning that the nutrients go straight to the roots. Plants grown using this method will typically grow faster than in regular soil because they are getting more nutrients on board quicker and delivered direct to their roots as oppose to searching for it in soil.

Another major advantage of using soil-less mixes is that you are much less likely to have issues with pests. Probably the most popular soil-less mix is Coco Coir mixed with perlite, Coco Coir is material that is made from coconut husk fibers, it was originally used in the 80’s in Holland to grow flowers. Because of its incredible success marijuana growers began to use it for hydroponic growing instead of using peat moss which is much denser.

The reason that Coco Coir works so well is that it retains water whilst also allowing for good drainage and aeration, it is also a good source of potassium and iron for the plant. Often when choosing growing mixes you do not need to choose simply between soil and soil-less mixes, usually the soil mixes will already contain some perlite and coco coir because it boosts the overall properties of the soil.

Growing cannabis using hydroponics

Hydroponics deep water culture is a method of growing cannabis whereby the roots of the plant are growing directly into clay pebbles and below that is a well of water. One of the advantages to using clay pebbles with hydroponics is that they provide plenty of space for the roots to expand and allow lots of oxygen to flow through keeping the roots fresh.

Hydroponics in general is an excellent way of growing cannabis because it provides a constant supply of water and nutrients to the plant so that it doesn’t have to work to find and absorb it from soil, because of this cannabis plants tend to grow faster.

Nutrients are delivered directly to the roots and trickle through the pebbles, into the water well below, the water is then recycled and used again to water the plants meaning that you can also save on water.

​The downside to using hydroponics in my opinion is that regular maintenance is required which is a lot more hassle than just planting in soil in your back garden and you also need to keep a close eye on the nutrient supply. It is very common for growers using hydro to have to regularly alter the PH PPM levels in the water and hydro grows also can eat into your electricity consumption. However if you are an experienced grower and can give your plants the time and care to do a hydro grow I would strongly recommend it!

growing weed in hydroponics

Joe Musgrave

Joe Musgrave is a keen 420 blogger who writes about all things cannabis. After harnessing his green thumbed skills through years of working on cannabis farms, Joe now shares his knowledge with the rest of the online 420 community.

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