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Best Grow Media For Cannabis

Written by Neal Brown . Updated: January 15, 2021

Hydroponic Growing with Different Mediums

In the wild, most plants, including marijuana plants, use soil as a grow medium. Indoor growers have another alternative, though. They can use hydroponic systems featuring various grow media to exert more control over nutrient distribution and maximize their yields. This option is a great asset to growers where the laws may still be unfavorable towards growing (like Kansas or Tennessee or in states where the weather simply demands indoor growing options, like Alaska or Wisconsin.

Weed plants grown in hydroponic setups have easy access to nutrients and carbon dioxide, which improves their efficiency and, in some ways, makes them easier to grow. Plus, today’s hydroponic growers have more options at their disposal than ever. Hydroponic systems require a substantial initial investment, though, so read on to find out about different grow media before investing in equipment to find the one that will be the best fit.


This light-weight, affordable mineral-based material is great at retaining water. It’s composed of basalt and silica compound and can be bought in different quantities depending on the scale of the hydroponic grow. Growers can purchase large, one square meter plaques of rock wool, small blocks of concentrated substrate, or bags of shredded material.

One of the best things about Rockwool is that it retains water well. That means growers don’t need to water their plants as often, which can cut back on both labor and costs. Just make sure to check the plants every day for signs of under-watering or over-watering.

In any hydroponic system, over-watering is actually just as dangerous to the plants’ health as under-watering because it deprives the roots of oxygen and places the plants at higher risk of being attacked by mold and other fungi. Keep an eye on the plants, hydrate them gradually, and avoid reusing water to help prevent fungal growth. Hydroponic systems that use Rockwool as a grow medium should never feature platters beneath the plants, as this encourages over-watering.

It’s equally important to purchase the right type of Rockwool. Never use the so-called “isolation” form of Rockwool, which contains chemicals that inhibit plant growth. Instead, purchase Rockwool specifically intended for hydroponic cultivation.

Pros of Rockwool

Rockwool is popular with commercial growers. It’s affordable, efficient, and great at retaining water, which makes it a good solution for grows of all sizes.

Cons of Rockwool

No substrate is perfect, and Rockwool is no exception. For one thing, it’s naturally alkaline, which means growers must neutralize it by applying an acidic solution of around pH 4 or 5 before using it for their plants, which takes a full day. Dry Rockwool is also a skin and lung irritant, so growers must wear protective gear like gloves, long sleeves, and breathing filters when working with the dry material. Once it’s been moistened, this isn’t as much of an issue.

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