In my 20+ years of growing cannabis I’ve tried most types of grow media. Whether you call it grow media or grow medium (used interchangeably from what I can tell) it’s the material where your roots live.
The purpose of grow media is to provide structural support for your plants, insulate roots from temperature extremes, hold moisture and air space (oxygen), hold and exchange minerals and nutrients, and create a home for beneficial biology in your root zone.
Soil (good old dirt) is the most well known media for growing plants. However, roots can thrive in a wide variety of materials if given the proper water, air and nutrients within a controlled temperature and PH range.
Foxfarm Ocean Forest is an excellent organic soil for beginners and professionals alike. It comes pre mixed with a wide range of organic nutrients for optimum plant development. I used this soil with great results for many years.
Even with a great premixed product like this though, you can run into problems. Over watering is an easy thing to do in soil, and leads to multiple, sometimes difficult to diagnose, issues. If you want to really push a plant to produce it needs extra light, CO2, and nutrients. There’s no use boosting your light and CO2 if you can’t boost nutrients too. This means feeding more, and that’s tricky to do in soil.
Coco coir is the inner pith of coconuts. Moving from soil to coco media allows for daily feeding without the risk of over watering. It’s nearly impossible to overwater in coco. The main cause of health issues with overwatering is suffocation. Roots need oxygen, and soggy muddy soil prevents roots from getting the oxygen they need.
There are many types of coco coir available and I’ve tried many. You can buy bricks of compressed coco in at least three different textures. The chips were my favorite, and made beautiful ground cover around the yard when I was finished. Coco also comes in blends with additives and perlite. This is ready to use and looks like regular potting soil. Coco by itself has little nutritional value so if you choose coco you’ll need to add fertilizer to your water. Many nutrient lines have a coco specific option.
There are a variety of media options for hydroponic growers. Rockwool, perlite, and clay pellets are a few.
I use rockwool for clones but have never tried using it for bigger plants. Many commercial indoor growers use it because of its cleanliness and ease of disposal.
Perlite is regularly mixed with other mediums to add drainage and aeration. It can be used on its own though. I’ve used it as a mix ingredient and also tried adding to the bottom of containers for drainage. Like the rockwool, I’ve never used it for hydroponic growing.
Clay pellets are commonly used for hydroponic cannabis. They are easy to clean and reuse which makes them cost effective and environmentally friendly. I tried this method once on a large scale medical grow with disastrous results. After the plants grew big and healthy they started to wilt and die one by one.
Deep Water Culture is a method of growing where the roots grow directly in a reservoir of nutrient solution. I tried this once and despite claims of higher yields, this was not my experience. While the plants looked very healthy and grew very fast the buds were about half size.
There’s a movement towards permaculture and more natural ways of growing cannabis. In the future I’m very interested in trying a no till, living soil, compost tea type of growing. For indoor or smaller container growing in greenhouses I would still use coco. The ability to feed every day, immediately adjust nutrient levels, and flush completely has proven unbeatable in my opinion for high yields of quality cannabis.