A lot of new marijuana home growers will prefer to use soil as a growing medium, which, to the uninitiated, makes a lot of sense. After all, most plants seem to grow well in it, so why should marijuana be any different? In fact, it may sound odd to most people why some would not want to grow their plants in soil.
However, you may be surprised to know that soil is hardly the ideal growing medium. Experienced growers may even argue that it is actually the worst for growing weed. Let’s find out why this is and what other growing mediums can be used to maximize the growth and yield of your cannabis plant.
What does cannabis need in a growing medium?
While soil has its place in cannabis growing, it is definitely not essential. Most plants only need a few simple things in a growing medium to thrive and it’s so mind bogglingly simple: if it allows the roots to get water, oxygen, and nutrients, you can use it!
Now, this can be almost anything. However, there are only a handful of materials that have been proven to get good results at a reasonable cost for growers around the world. Below are some of the most popular choices for growing mediums recommended for home growing purposes. Let’s look at the advantages and disadvantages of each.
Soil is still a popular growing medium for cannabis especially for beginners since it is readily available and is kind of a no-brainer to use. However, it does have some significant drawbacks when compared to other growing mediums.
- Cheap, practically free.
- Organic. May contain beneficial bacteria that can positively impact plant health and nutrient uptake.
- Some growers say that it produces the best-tasting weed.
- The plant can support itself from its roots.
- Nutrient and pH content can be harder to manage compared to hydroponic systems.
- Not sterile. Can be a magnet for pathogens, diseases and pests.
- Yields are not as big in comparison to hydroponics.
Those who grow using soil typically use specially formulated potting soil and almost never regular garden soil. This has the right consistency conducive to root growth and often comes with the right mix of nutrients from organic materials such as worm castings, bat guano, aged forest products, crab and fish meal and even beneficial bacteria. This kind of soil is ideal for beginners who want to get the hang of growing in something more basic and familiar.
Coco coir is made out of various coconut fibers, typically a mix of the pith, fibers, and chips in different ratios to provide the right texture. Coir is good at retaining adequate moisture and aeration and can be used on its own, as a soil additive or a substrate for hydroponics.
- Retains and drains water adequately.
- Allows good root penetration and oxygenation.
- Organic and versatile.
- Biodegradeable and environmentally sustainable.
- Inert, pH neutral and can inhibit pests.
- Provides a conducive environment for beneficial microorganisms.
- May need washing since it is initially high in salt and treated with certain chemical agents.
- Needs a specific nutrient blend since it can lock out nutrients like calcium, magnesium, and iron.
Rockwool is basically molten rock spun into threads then compressed into blocks or sheets. Because of this, it is often an alternative for coco coir and is a popular rooting medium for seedlings and clones, as well as a substrate for hydroponics.
- Great at keeping adequate moisture and aeration.
- Versatile and reusable.
- Completely sterile.
- Rockwool can cause skin and eye irritation and lung problems if handled improperly.
- Beneficial bacteria may have a hard time thriving in rockwool.
- May initially have high pH.
- Disposal can be a problem since it is non-biodegradable.
Like coco coir, rockwool needs to be pre-treated by soaked before use to get rid of its excess acidity. Despite environmental concerns and health hazards that it may pose, rockwool is still one of the most popular growing mediums especially among hydroponic growers because of its properties, durability, reusability
Peat or Sphagnum moss
Mosses are a fuzzy, stringy type of plant and the one often used as a planting medium typically comes from bogs. Sphagnum is the live plant while peat moss is the dead plant material mixed with other materials in the bog. Both have been used as a potting medium or as a soil amendment.
- Organic and sterile.
- Has good water retention capabilities.
- Soft and allows good rooting.
- Sphagnum moss is relatively inexpensive.
- Sphagnum moss is pH neutral while peat moss is naturally acidic.
- Peat moss is not environmentally friendly or sustainable. It takes hundreds of years for peat moss to form in bogs and harvesting it releases CO2.
Sphagnum is typically only used as soil amendment and not as a sole growing medium. While peat moss can be used as a growing medium and soil amendment , growers now tend to shy away from using it because of its impact on the environment.
Perlite & Vermiculite
Perlite is made from volcanic glass while vermiculite from hydrated magnesium-aluminum-iron silicate. Both come in the form of small pellets or grains and are used as a growing medium for hydroponics or mixed with soil.
- Improves water retention and aeration when mixed with soil.
- Sterile, inert, and pH neutral.
- Does not decompose and can be reused.
- One of the preferred growing mediums for hydroponics.
- Relatively inexpensive.
- Versatile and can be used in a number of growing applications.
- Great for germinating and rooting seedlings since roots won’t get stuck and can easily be removed.
- Non-renewable resource.
- Perlite pores can get stuck with dirt.
- Perlite dust can be harmful when breathed in.
Even though both are mineral products with similar appearance, you cannot use one in place of the other due to a few key differences. Vermiculite holds moisture longer while perlite drains faster, provides better aeration and helps prevent root rot. This doesn’t mean that one is better than the other, it’s just that one may be suitable for a particular setup or you may also need to use a mix of both in varying ratios.
Hydroton (Clay pebbles)
Hydroton, also known as LECA (light expanded clay aggregate) are nothing more than clay pebbles the size of peanuts or small marbles. This versatile planting medium can be used on its own, mixed with soil, or in hydroponic or aquaponic systems.
- Promotes better percolation of solution.
- Doesn’t get clogged and drains effectively.
- Environment-friendly and reusable.
- Does not constrict roots and allows easy transplantation.
- Does not hold moisture and thus better used for setups with continuous flow of water.
- A bit more expensive than other growing mediums.
- Can absorb moisture from your plants if left to dry.
- May increase pH levels.
In the simplest sense, a hydroponic system is where the surface of your plant’s roots are exposed mostly to water or nutrient solution. Experienced growers favor this method as it typically runs on its own but brings the best yield, if done correctly. We discuss some of the most popular hydroponic setups for marijuana in Basics on Setting Up Hydroponic Grow for Cannabis.
- Good yield.
- Mostly automated.
- Efficient use of water and nutrients.
- Needs some experience to set up.
- System failure could wipe out all your plants.
- You’ll need to invest in equipment.
Frequently Asked Questions about Growing Mediums
There is no one “best” growing medium for cannabis or any plant for that matter. The choice largely depends on your growing setup but there are some popular choices that most growers like to use in combination with others. These are potting soil, coco coir, and water (hydroponics).
If you want a healthy cannabis plant that will give you a good yield, never use regular garden soil. Instead, use organic potting soil formulated especially for growing marijuana. This will have the right texture conducive for root growth, water retention and proper aeration. It’s also likely to contain the necessary nutrients and beneficial bacteria for your plants.
Perlite and vermiculite are good growing mediums that are typically used to improve the consistency and texture of soil. Both are also often used in hydroponics by themselves or mixed together in a specific ratio since vermiculite holds water better while perlite provides better aeration.
Hydroton, also known as LECA (light expanded clay aggregate) is a popular growing medium since it provides good root oxygenation and allows better solution percolation. It is also environment-friendly and sustainable.
Coco coir is one of the best and most popular growing mediums because of its numerous benefits which include good moisture and nutrient retention. It is also cheap, environment-friendly, sustainable, and completely organic.
Rockwool is a popular growing medium since it is completely inert and sterile, has a good density that’s conducive to rooting, holds adequate moisture and allows good aeration, and can be reused multiple times. However, it is not so environment-friendly and can cause pose a health risk if improperly handled.
While peat moss is a decent growing medium that is often used to amend soil, it is no longer as popular as before since it is not environment-friendly.
As you may have guessed, there is no single “best” growing medium. Rather, there are some that are more suitable than others in a given setup. Most of the time, growers also combine these materials to compensate for any disadvantages one medium may have. In fact, even potting soil is rarely used on its own, most growers would mix it with some perlite or vermiculite.
If you are a new home grower, the best way to get to know these growing mediums would be to start with amended soil first. Once you’ve gotten the hang of growing a particular strain and are confident enough to increase your yields, you’re probably ready to start experimenting with a hydroponic setup.