Rockwool

The most popular medium for hydroponics

Rockwool is the medium that is most used for hydroponics. It is favored because of its ability to simultaneously hold a large quantity of water and air. Its composition and texture is also well-suited to aiding in plant stability.

Rockwool is made from basalt rocks and chalk. These two items are heated to temperatures as high as 3000 degrees Fahrenheit, at which point they become lava. They are then put into a spinning chamber and are spun together into fibers that resemble the texture of insulation or cotton candy.

These fibers are then compressed into large slabs or cubes. Rockwool can be used as a growing medium from the time of propagation right through to harvest. Small rockwool cubes are typically used for the propagation of hydroponics plants. Seeds can be planted into the cubes. Once the plants reach the proper level of maturity, the cubes can be transplanted to larger cubes or moved on top of rockwool slabs. The roots of the plant can then grow down into the rockwool slab, similar to the way roots grow into a perlite grow bag. A standard rockwool slab is big enough to support three or four plants.

Conditioning Your Rockwool

Rockwool has a naturally high pH, which is very damaging to plants. Because of this, rockwool needs to be conditioned before it is used. To correct its pH level, rockwool should be soaked in water with a pH between 5.0 and 5.5. After it has soaked, rinse the rockwool with pH 7.0 water. Cubes are small enough that they can be placed into a bucket to soak. They should be left submerged in water for around eight hours. Because of their size, rockwool slabs can be harder to soak. Don’t worry - you don’t need to give up use of your bathtub for the evening. The best way to soak a slab is to simply cut a small hole in the plastic bag the rockwool is sold in and then fill the bag with water. Slabs should be soaked for 24 hours.

An Environmentally-Friendly Medium

Rockwool can be reused for several harvests and then put into a soil garden or compost to biodegrade. Much of the raw material used in the manufacture of rockwool is recycled, in the form of slag from producers of ferrous and non-ferrous metals. A single cubic yard of slag can be turned into over 35 cubic yards of rockwool.

Safety Precautions

When dealing with dry rockwool, it is essential to avoid handling it with bare hands. Also, be sure not to inhale any rockwool fibers. Although it is non-toxic, rockwool can cause skin irritation. Always wear a dust mask and gloves when handling dry rockwool. If skin irritation occurs, rinse the area with water.