Some people claim they use a diluted nutrient solution to water their Rockwool cubes with during germination. Do not do this, as my experience has always been negative. Note the picture below, where I did an experiment by adding a very diluted grow nutrient to the Rockwool cube on the far left. It died within an hour or two, and the others went on to live happy lives. In my opinion, they do not need nutrients until they get into your hydro system.
Get a bowl or some other container that is big enough to fill with water and have room left for your Rockwool cubes. Your average salad bowl will work fine for 3 Rockwool cubes, if you are planning on doing more than you will need a larger container.
To accomplish this, use either Ph down chemicals, or lime juice (as it’s acidic). Add these to the water in small increments (VERY SMALL), and test the water to see where the Ph is. Continue doing this until you have a Ph of 5.5-6.
Important: Do not let the PH of the water go below 5. A Ph this low will damage the fibers of the Rockwool Cube
On top of that, Rockwool is like asbestos, you don’t want to be squeezing it or breathing it or generally touching it any more than you need to. Here is a good article on some of the health concerns of Rockwool. I use it because it is what works best, but be cognizant to the fact that it is a potentially dangerous substance to be making contact with so don’t do anything more than you need to with it.
Do not add any nutrients to your Rockwool Cubes. The one on the left got nutrients, the other two did not.
Fill the container/bowl with water from your tap. You may also choose to use water filtered through a britta or reverse osmosis (R/O) water, I’ve had success with all 3 of them so whichever you have on hand will work fine.
They should look like this:
For one, Rockwool doesn’t contain any organic material. This means it’s immune to decomposition at the hands of mould and fungi. Rockwool is also free from heavy metals. These elements, such as lead and chromium, are highly toxic to plants, cause yellow leaves and prevent photosynthesis, and can even kill plants altogether.
Second, consider wrapping a rubber band or soft garden tie around the middle of the cube to ensure it doesn’t break in half during the next grow.
How Is Rockwool Made?
After harvest, reclaim your cubes! If you plan on reusing them, submerge them in boiling water and give them a clean. If not, shred them up as finely as possible and dump them on the compost pile.
In this guide, you’ll learn everything you need to know about this robust material. Find out why to use Rockwool in both hydroponic and soil systems, how it works during every stage of the growing cycle, and much more.
Flush your soil or hydro plants one week before harvest. Restrict nutrients and only provide water to remove excess salts from the soil and allow plants to use up the last of their supplies. This will result in tastier and smoother buds.