There are several different types of growing media that can be used to successfully grow cannabis plants, but what are the pros and cons of each, and which one should you choose for your grow setup? In this article, we’ll discuss some of the primary growing medium options and what each one has to offer.
Rockwool started as a type of insulation, but about half a century ago a composition was created that works well for growing plants. That kind of rockwool, horticultural rockwool, is commonly found for growing a variety of plants. The beauty of rockwool is that it is easy to use, can be chosen in the size that works for you, and can be especially useful when growing marijuana in trays.
It is not a naturally occurring material; instead, it is human-made. It contains metal oxide or a fiber material via high pressure and heat, and it works well for hydroponics because of how much air and water it is capable of holding. It also is considered to be extremely breathable, meaning it can take in nutrients quickly and allows for extensive and easy root growth. It even helps stabilize the plant.
The best way to use rockwool is by having 1-inch cubes to start your marijuana plants in. You can then move the plants to larger cubes, easily adapting and growing into them without any danger to the roots. Rockwool can also be cut into slabs to grow multiple plants within one rockwool unit.
If you are looking to buy rockwool, get a type that comes from basaltic rock. This is because the mineral content of basaltic rock is non-reactive and is inert, although its high metal content could potentially be reactive to the nutrients you use. Make sure you buy it from a hydro shop since rockwool generally has a higher pH level (8.0). If you soak it in pH 5.5 water for an hour, you can neutralize it.
As interesting as it sounds, perlite is made from an amorphous volcanic glass that was expanded and turned into granules. The advantages of perlite include the fact that it is a neutral pH level, is very porous but still holds water well. It does especially well for cutting and seedling transplantations. Perlite also works well inside of containers because it is so lightweight.
Sometimes perlite can be an issue in hydro setups because of its dustiness, which tends to clog pumps. Often perlite bought in a gardening center was already treated with fertilizers, which is not okay for young marijuana plants. It should, therefore, be washed before use, especially if you’re using it in a hydroponics setup. Wear a mask when working with perlite because of the dust it produces.
One major downside to perlite is the fact that it does not provide marijuana plants with much stability, so instead of using this medium on its own you can look into mixing it with another type of media for higher support.
Vermiculite is made from mica and clay that has been put under high heat until it expands. Like perlite, it is very light, retains water well, and is porous. It also does not provide much support for marijuana plants and therefore works best in combination with other media.
4. Clay pellets
Also known as LECA (lightweight expanded clay aggregate), clay pellets are just what they sound like – balls of clay that have been expanded with heat to make them porous. They are some of the most commonly used media, perhaps due in part to the fact that they are naturally pH neutral and sterile, can be flushed out and reused easily, and even support the roots of cannabis. Still, they allow for excellent aeration and water drainage.
One of the great things about clay pebbles is that beneficial bacteria can grow while water and nutrients are retained. Be sure to wash out the clay pebbles before each use (including right when you buy them). Most clay pellet mixtures come from Hydroton or Hydrokorrels (which design for hydroponics growing systems specifically).
Coco or coco-coir is gaining popularity in recent years. It comes from the fibers of coconut husks and breaks down slowly (unlike peat moss), allowing for reuse. Getting coco is more environmentally friendly than its alternative, peat moss, since the latter destroys bog ecosystems. Drainage is good in coco, and aeration and water retention are also good. Coco comes in bricks, croutons, or mats.
The term “soil” is used to describe a wide variety of substances, including compost, manure, fir bark, peat moss, sand, perlite, and other materials. If you buy soil from a store, it likely will also include fertilizer of some sort. The key is not to have an overfertilized product for young plants, as it will “burn” them. Many growers prefer to grow in soil because they claim the taste of marijuana grown in soil (within a hydroponics system) is superior to other growing mediums.
Soil does a good job in maintaining a consistent pH level, as well as adding a cushion for any possible mistakes or errors in watering schedules (such as a mechanical breakdown). It gets pricey when you are growing several plants, however, and it can require a lot of work (and cause a lot of mess).
If you do want to use soil, make sure it has the right texture, water retention level, and drainage ability. Many growers will add in a tenth of perlite or another medium to keep the soil more porous. Never take soil from outside, as it could contain any number of unexpected diseases and pests. Soil cannot be reused for future grows, unfortunately.