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Perlite
Definition: Perlite is a lightweight white soil amendment made by heating volcanic glass until it pops into porous, popcorn-like granules. Mixed into soil or coco coir, it creates air pockets that improve drainage and keep oxygen around cannabis roots, helping prevent the waterlogged conditions that lead to root problems.
How Perlite works
Roots need oxygen as much as water. In dense, fine-textured mixes, water fills every gap and air has nowhere to go. Perlite’s rigid granules keep those gaps open, so excess water drains and fresh air moves back in.
How much to use
- Bagged potting soil: add 20 to 30% perlite by volume if the mix feels heavy.
- Coco coir: 30% perlite is standard; up to 50% for very frequent watering.
- Living soil: roughly one-third aeration, which can be perlite or a substitute.
- Seedlings and clones: straight perlite or a perlite-heavy blend roots cuttings well.
Choosing a grade
Coarse grades work best for cannabis containers. Fine perlite packs down and loses much of its benefit.
Properties
Perlite is sterile, chemically inert, and close to neutral pH, so it doesn’t feed plants or change your nutrient balance. It holds a little water on its surface but releases it easily.
Handling tips
Dry perlite is dusty. Wet the bag before pouring and wear a dust mask when mixing large batches.
Drawbacks and alternatives
Perlite is so light that it floats to the top of pots over time, and it doesn’t break down, so it lingers in garden beds. Pumice does the same job, weighs more, and stays mixed in. Rice hulls are a renewable option common in living soil recipes.
A well-aerated mix is one of the simplest defenses against overwatering, especially for beginners still learning how often to water.