Understanding The Basics of Cannabis Grow Mediums

Thousands of cannabis grow mediums are sold out in the stores and online today, and knowing which one to choose easily becomes overwhelming.

Cannabis cultivation has come a long way over the years. The introduction of hydroponics and soil-less mediums changed the way cannabis was grown forever. While you are likely to find soil in an outdoor or organic grow, mediums like cocoa coir, vermiculite and perlite are often found in your large scale commercial grows. The types of medium you use will largely revolve around the results you are trying to get and the techniques you wish to employ. Here are some of the more popular mediums you will find in today’s cannabis grow rooms.


Good old fashioned soil is rich with elemental nutrients, microbes and fungus which supply a large part of the nutritional regimen of your plants. Soil can be used in any grow, however, the organic nature of soil doesn’t work well with standard nutrient salts. In nature, soil acts as part of the ecosystem, and houses many forms of microbes. These microbes transform nutrients in the soil into a form more readily available for absorption by the root system. In nature the fungus in the soil is essential to plant growth. Unfortunately, nutrient salts kill these microbes, which means soil should be used for organic, preferably outdoor cultivation only.

Coco Coir

Coco coir is probably the most used hydroponic medium in cannabis cultivation today. Made from the husks of coconuts, coco coir is a soil substitute pH and EC neutral. Being a neutral medium means that it does not add to the acidity or nutrient balance of your feed mix. Coco can hold many times its weight in water, which keeps your roots wet at all times, even between feedings. Coco is also sustainable and environmentally friendly. Coco essentially replaced peat moss, which had to be harvested from sensitive wetlands. You will typically find coco ground up (coco pith), shredded (fibers) or in large chips. Coco is by far the most flexible medium which has made it the grower’s choice for cannabis.


Perlite is an additive mixed in with your soil or coco that provides greater air flow around the root system. Perlite is made from super-heated volcanic glass. When heated, it expands to more than ten times its original size, making it extremely lightweight and full of tiny air pockets. The perlite also absorbs water and holds onto it for added retention. When mixed into your soil, it breaks up the consistency, making it less dense and allowing for increased aeration. You will often find perlite mixed in with a medium at varying ratios depending on the water needs of the strain.

Clay Pebbles

Expanded Clay pebbles are one of the lesser seen but very effective soil substitutes. They are basically light weight clay beads that replace soil in a hydroponic grow. They are completely neutral which allows for greater fine tuning of your feed mix. They are also reusable, which can save a ton of money in the long run. The clay pebbles are used by themselves, not simply mixed in with soil. This complete removal of traditional soil-like mediums prevents pests like root aphids, who would normally make a home in your medium. They are a little pricey, but being that you can recycle them forever makes them worth the purchase.


Rockwool is a hydroponic medium that is made from chalk and basalt. The ingredients are melted and then spun like cotton candy. The fiberglass-like strands are then compressed into a matt. From there the rockwool is cut into cubes or grow blocks. You can find ground rockwool, which can be used as your main medium, however more often than not, rockwool is used for germinating seeds or housing clones. Rockwool isn’t considered overly environmentally friendly and doesn’t breakdown over time, so if you are worried about mother earth, you might want to skip this one.

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