Basalt Mineral Wool: The Key to Perfect Irrigation in Your Grow Room

Commercial growers use basalt (or basaltic) mineral wool in their hydroponic growrooms, and you should consider using it, too.

What is mineral wool?

Also known as “stone wool,” mineral wool is manmade fiber spun out of rock. Although it can be spun out of a variety of rock types, mineral wool spun out of basaltic rock is recommended for grow rooms.

Note: While the trademarked product “Rockwool®” is made out of basalt rock and often used in grow rooms, it’s not a synonym for “basalt mineral wool” in general. “Rockwool” is a specific, registered trademark that belongs to Danish company Rockwool International.

How is mineral wool made?

The rock is melted, and much like cotton candy is spun out of melted sugar, mineral wool is spun out of the melted rock. Immediately after it is spun, binding agents are added to the fibers; then they’re compressed and cured into slabs. The slabs are then cut into smaller blocks or turned into granules. You can buy mineral wool in a variety of slab and cube sizes to meet your needs. Although mineral wool can be spun out of a variety of rock types, basalt mineral wool should be used in grow rooms.

Why basalt mineral wool is a popular material in hydroponic grow rooms

So-called basalt “horticultural mineral wool” is perfect for grow rooms because it’s extremely absorbent and breathable. It can hold a lot of water and air and is perfect for seed starting or “nutrient film technique” (NFT) grows. NFT is a “continuous flow” system whereby the nutrient solution flows continuously over the roots, which encourages excellent growth and abundant harvests.


• Basalt mineral wool holds water easily

This mineral wool feeds water to roots even when it’s almost dry. Plants in mineral wool won’t experience water stress until the mineral wool is almost completely dry. It also means you can give more pore space to air while still ensuring that roots get enough nutrient solution.

• Basalt mineral wool gives the root zone plenty of oxygen

As long as mineral wool isn’t completely immersed in water, it holds air at a proportion of about 18%, which means the root zone gets plenty of oxygen at all times.

• Basalt mineral wool gives roots stability

Roots quickly “latch onto” mineral wool cubes and slabs for a stable foundation.

• Basalt mineral wool comes in many shapes and sizes

This mineral wool comes in a variety of sizes and shapes to fit grow room needs. In addition to cubes and slabs, you can also find it in granular form.

• Basalt mineral wool is inert and nonreactive

Provided the mineral wool is spun out of basalt rock, it is pH neutral as long it is soaked in water and rinsed before use to achieve a pH of 5.5. (Most mineral wool comes with presoaking instructions.)

Some considerations

• Mineral wool should always be soaked and rinsed before use

While other grow mediums can be used immediately, basalt mineral wool’s pH will be too high unless it is soaked and rinsed first. However, it is pH neutral once this has been done, which makes it a very stable growth medium.

• It can cause lung and skin irritation

Use protection like gloves and masks when you handle dry mineral wool. It’s nontoxic, but the fibers can still cause irritation if inhaled or touching bare skin.

• It can be friendly to algae growth

Because it’s kept moist, using mineral wool can encourage algae growth. You can prevent this by shielding the mineral wool from light: Cover it with black covers, and shield nutrient tanks and other “wet” areas from light, as well.