Growing in Rockwool
Growing in rockwool is a sort of step towards hydroponic growing, as they’re both inert substrates meaning that there’s no organic material decomposing. This means that when you water this plant you’re going to need to fertilize it with the necessary nutrients so that your plant can grow vigorously and strong.
You can find various formats of rockwool to grow in. First, there are little 5x5x5 cubes used for germinating or clones, although it’s recommended to grow clones on a tray with 77 or 150 cavities, as it’s much more organized, or you can grow them in rockwool slabs as well. You can get larger cubes, 10x10x6.5cm, perfect for growing in both rockwool slabs and with the Gi Grow Wheel. Rockwool slabs are bags that measure 100 x 15 x 7,5 that contain rockwool. The biggest advantage that rockwool has over coco coir or soil is that it is an extremely airy substrate with allows you to grow abundant harvests without having to transplant and possibly damage the roots.
So, when you first begin growing in rockwool you might be a bit confused on how things work. The first thing you’ll need to do once you have the rockwool is let it soak in water, preferably with a pH of around 4.5-5. This pH level is important because it lowers the original pH from 7 to 6, allowing the plants to absorb all of the nutrients right from the start.
Once the pH is under control, you’ll need to move on to germination, cloning or growing. We usually recommend germinating using a plastic container and some kitchen paper. Once the roots are out of their seeds, you can move them to your rockwool cubes and begin growing. It’s important to control how much you water and humidity at this point. We don’t recommend watering too much or having constant water, as the roots need an opportunity to take advantage of the extra space and air that rockwool provides. This will also prevent the appearance of algae on the rockwool cubes. If you want to completely avoid these algae, you’ll need to keep the substrate completely out of the light like in this picture.
If you’re cloning, once you have your clone ready with rooting hormones, place it in the rockwool. The proportion of air will allow you to root over 7 to 10 days, avoiding any rot in the stem. You’ll also need to stabilize the pH in the rockwool to avoid any eventual root blockages. The irrigation will need to be controlled and automatic to make sure that the rockwool doesn’t get too dry and stress out the roots which would affect the final yield.
The biggest rockwool blocks are used with Gi grow systems; they’re placed in the racks and can easily deal with the weight of the plants. There are two versions, although the only difference is the size of the hole in the package.
These blocks can be used as an additional support for those that grow in rockwool slabs. The advantage to doing it this way is the amazing production rate, the comfort of not having to transplant your plants and the possibility of growing horizontally, vertically and in sand. Watering time would change horizontally and in sand, rising little by little to give more water each time, so as well as raising the amount of water you’ll need to increase the EC level; we recommend having an EC gauge handy for your grows. When growing vertically, you can water for as long as it needs for the water to reach the plant furthest away.
It’s important to remember that, just like with hydroponics and coco coir, it only takes a week to clean out the roots. This is due to the substrate’s low retention of salts and nutrients.
Author: Javier Chinesta
Translator: Ciara Murphy