Rockwool (Stonewool)

Last Updated: February 22, 2018

Definition - What does Rockwool (Stonewool) mean?

Rockwool is an inorganic insulator made from stones or rocks by blowing a jet of steam through molten rock (such as siliceous rock or limestone) or slag. More advanced production methods involve spinning molten rock in high-speed spinning heads.

Rockwool is widely used as a soilless growing medium for plants and comes in various forms and various sizes to suit various types of gardens, 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.

Rockwool may also be referred to as stonewool.

MaximumYield 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.

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