Rockwool has been one of the best mediums for hydroponic cultivation for nearly 50 years, but what exactly is it?
In short rockwool is basalt, a volcanic rock, that is melted back down into lava, then put into a spinning machine where it is processed similarly to cotton candy. The liquid is spun until it becomes fibrous, then pressed into cubes to create the rockwool cubes we all know.
Rockwool is favored by hydroponic growers due to its inert and sterile properties, plus the ability to hold water better than other soilless media. Growing in rockwool is different from your average soil or other soilless media, however.
One of the many benefits of rockwool is its ease of use. There are however some tips for maximizing the effectiveness of your rockwool cubes in your hydroponic grow.
Firstly, keep the rockwool in the wrapping in which it comes. It might seem natural to take off the packaging of your rockwool cubes, however there's a reason to keep it on.
If you think of each rockwool cube as a pot, the wrapping on the outside is the pot itself. The wrapping helps to keep moisture and nutrients in the rockwool cubes longer, and prevents them from drying out too quickly.
Speaking of moisture, make sure to pre-soak rockwool cubes prior to planting your seeds or cuttings. Unlike normal soil, rockwool should be soaked in a nutrient solution for as long as necessary to achieve a desired pH of 5.5.
As the solution seeps into the rockwool cubes, tiny air bubbles will escape the crevices of the rockwool. When the bubbles stop rising, you'll know the cubes are properly soaked.
Make sure to let the rockwool cubes naturally drain any excess water until they are no longer dripping. Doing so will allow some air to re-enter the rockwool cubes to create a balance between air and water.
Another huge benefit to rockwool is that it allows instant access to nutrients for your plants. Because rockwool cubes do not lock out any fertilizer, whatever you put in will immediately become available to the plant or ready to flush out of the bottom.
For this reason, one should always allow for sufficient runoff between feedings, as plants take up water faster than nutrients. This process will leave fertilizer salts in the media, which will be pushed out with the next feeding of fresh nutrients. Failure to run-off properly can result in salt buildup in your rockwool cubes which can eventually damage your plants.
It may be tempting to even squeeze the rockwool cubes to remove some excess water, however we strongly advise against this. The unique structure of each rockwool cube is responsible for its water retention properties and air circulation which allow roots to develop.
If squeezed too much, rockwool cubes can become deformed, removing pathways for roots to grow as well as the pockets for aeration. In other words, squeezing rockwool cubes is not worth it!
Lastly, a big advantage to rockwool is that it can be reused and recycled. It is a common misconception that rockwool for hydroponic cultivation and rockwool used in housing insulation are the same thing. This has led to unwarranted concerns regarding toxicity and disposal of rockwool cubes.
The basalt which makes up rockwool is a beneficial amendment to plants in its crushed rock form. However you do want to avoid planting starter plants into used rockwool cubes, and reusing any grow media in general repeatedly for the same plants.
Overall, rockwool is a great option for hydroponic growers looking for a soilless medium that still holds on to water and nutrients efficiently. Rockwool cubes are cost effective and can help grow healthy, large plants that can yield more than traditional media when managed properly.
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