Rockwool is perhaps the most popular medium used by hydroponic growers today. When you look at the numerous benefits, there is little wonder why. It retains moisture well, so there is less chances of underwatering. It retains oxygen well, so there is less chance of overwatering. It never impedes the development of roots. And it comes in numerous sizes and shapes, so it accommodates just about anything you could want to grow. But with these advantages come certain special concerns that every user of rockwool should take into account.
Environmental Concerns – Though a similar substance is made naturally by volcanoes, the rockwool that is used in hydroponics is not really a natural material. The substance is made by taking chalk and rock and heating them to three thousand degrees Fahrenheit. It is then "spun" and cooled, turning it into the material you see at the hydroponics store. Because it is not natural, it is not biodegradable. Any rockwool that you dispose of will sit in a landfill indefinitely. If you are concerned about these environmental issues, but still want to get the benefits of rockwool in your hydroponic garden, you should try to avoid purchasing new rockwool cubes every growing season. Instead, you should thoroughly rinse your old rockwool of any organic material and reuse it. This won't just be better for the environment, it will also save you a great deal of money.
Health Concerns - You should be extremely cautious when handling rockwool. It can be irritating to the skin, eyes, and lungs. Too much exposure to the skin might even cause serious long-term effects. The skin irritation isn't caused by any chemical danger in rockwool, but rather it's physical makeup, much like how wheat or grass might cause irritation if it comes in contact with the skin. While there is not any real evidence that rockwool causes cancer, the Environmental Protection Agency lists it as a "Group 2B" material, which means it is "possibly carcinogenic to humans." To reduce your risk of any health complications, always wear a dust mask, goggles, and gloves when handling.
Ph Problems - By itself, rockwool is much more alkaline than other media, which means that you may have to make special adjustments to your nutrient solution pH to create an ideal pH for the root zone. This can be troublesome if you are using multiple media, as it might require you to create one pH balanced nutrient solution for one media and a separate one for your rockwool-grown plants. Rockwool can also shift its pH balance fairly rapidly, which means you may have to be extra vigilant about regularly checking your pH balances and making necessary adjustments.
Pre Treatment - Unlike most other media, rockwool needs to be treated before it is used for hydroponics. You should soak it in pH treated water for a full day before you transfer your plants into it. For most it isn't a major a concern, it simply means that it is a bit more labor intensive than other hydroponics media.