Rockwool (Stonewool)

Last updated: May 18, 2021

What Does Rockwool (Stonewool) Mean?

Rockwool, or stonewool, is a type of soilless horticultural grow medium that is used in hydroponic systems for all types of crops like flowers, tomatoes, and lettuce. It is also especially good for growing cannabis plants.

Rockwool is finely spun volcanic rock (basalt) that resembles fiberglass insulation. It can be made by spinning molten rock in high-speed heads (think of cotton candy) or blowing a jet of steam through molten rock.

Rockwool comes in an assortment of forms and sizes to suit a variety of garden types, including rockwool slabs, rockwool cubes, and loose rockwool chunks. Cubes are popular for starting seeds, and once they germinate and become seedlings, the cubes can be transplanted into slabs.

Seedling sprouting from a cube of rockwool hydroponic grow media.


Maximum Yield Explains Rockwool (Stonewool)

Rockwool is a popular soilless growing medium for gardening and hydroponics because it holds water well and allows air to circulate the root zone for exceptional plant growth. Its strength makes it suitable for root support. In the hydroponics industry, rockwool competes with other types of grow mediums like grow stones, clay pebbles, coco coir, Oasis cubes, floral foam, vermiculite, perlite, and gravel.

Rockwool is lightweight, and can be reused. It provides a sterile growing environment for plants, and although it starts out with a naturally high pH, with proper conditioning its pH can be stabilized to make it suitable for plant growth.

The fibers in rockwool are abrasive and can release microparticles that can irritate or itch when in contact with the skin. For this reason, growers will often soak the rockwool before planting. Furthermore, rockwool should not be used in residential areas with high moisture levels (such as most basements) because fibers can absorb moisture and become a medium for mold growth.

In addition to being a popular soilless grow medium, rockwool is used in a wide array of applications and products due to its very high melting point and because it is an excellent insulator. For example, it is often used for fireproofing, fire stops, and other temperature-sensitive applications such as cooking appliances.

When sourcing rockwool for your hydroponics system, do a little bit of research beforehand to make sure you end up with horticultural-grade rockwool.



stonewool, mineral wool, Rock Hydroponics

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