Choosing the Right Substrate: Coco Coir, Gypsum & Grain Explained

Once you move past pre-made grow kits, one of the first decisions you'll make is what to actually grow in. "Substrate" covers a wide range of materials, and different species and methods call for different combinations. Here's what each of the common substrate components does, and how they fit together.

Coco Coir: The Base of Most Bulk Substrates

Coco coir is coconut husk fibre, and it's the base of most bulk substrate mixes because it holds moisture well without becoming waterlogged, and it's cheap and widely available in compressed bricks. On its own it's low in nutrients, which is actually useful: it gives mycelium a clean, low-contamination base to colonise before you add anything richer. Most growers rehydrate a coco coir brick and mix it with other components rather than using it alone.

Agricultural Gypsum: Balancing pH and Structure

Agricultural gypsum (calcium sulfate) gets mixed into bulk substrate to buffer pH and improve structure. It helps the mix hold its shape without compacting into a dense, airless block. It's a small addition by volume, but it makes a noticeable difference to how well a substrate breathes and drains. Most growers add it at a small percentage alongside coco coir and vermiculite rather than using it on its own.

Wheat Bran, Rye Grain and Vermiculite: Nutrition and Aeration

Wheat bran and rye grain add nitrogen and other nutrients that pure coco coir and gypsum don't provide, giving mycelium more to work with as it colonises. Vermiculite is different: it's not a nutrient source, it's there to hold extra moisture and keep the mix light and airy. Most bulk substrate recipes draw on some mix of these components rather than any one alone.

Putting It Together

You don't need to source and mix every component separately if you'd rather not. Our ready-made CVG bulk substrate mix combines coco coir, vermiculite and gypsum in tested proportions, so you can skip the calculations and start inoculating sooner. It's a solid default for most gourmet species, and a good option if this is your first time mixing your own substrate.