How to Use Rockwool Cubes for Plants
In a process similar to that used to make cotton candy, basalt and chalk are spun into Rockwool, which is turned into cubes. Rockwool is a brand name; the generic term is rock wool. Rockwool cubes, 1 or 2 inches wide and 1 1/2 inch deep, are used for germinating seeds for seedlings that are then transplanted into soil or hydroponic gardens. Cubes 3 and 4 inches wide are used as a primary growing medium for small plants. Rockwool has a high pH, so you have to adjust your water or growing solution to fit the needs of your plants.
Test your water’s pH with a test kit. After you drop 2 or 3 drops of solution from your kit into 1 quart of water, it will normally turn green, meaning it has Rockwool’s usual pH of 7 to 8. Add drops of lemon juice to the water until your kit indicates it has a pH between 5.5 and 6.5, the range that plants usually like. Water below pH 5 will damage the Rockwool fibers. If the pH goes below 5, add more water.
Soak the Rockwool cubes in the water for 1 hour to stabilize them. Rockwool contains fibers that are dangerous to your lungs if you inhale them. Wear a dust mask when handling the cubes.
Insert seeds in the hole on top of the cube. Insert two seeds for basil, broccoli, cabbage, cucumbers, eggplants, peppers and tomatoes and six to eight seeds for herbs.
Place the cubes containing the seeds in a nursery tray at 70 to 80 degrees Fahrenheit.
Water every one or two days or use a formulated nutrient solution used for hydroponic growing. The seeds should begin to sprout in a day or two. The roots will show through the bottom of the cube.
Transplant to a soil or hydroponic garden when the plant is 2 to 3 inches tall and has three or four leaves. Most plants take one to three weeks; tomatoes and peppers may need a week longer.
Make a hole in your planting soil or mix that is large enough to accommodate the cube containing the seedling.
Water your seedling with tepid water.
Place the cube with the seedling into the hole in the planting soil or mix. The cube should stick out a bit; the surface of the cube should not be lower than the surface. This prevents puddles from collecting the surface, a cause of root rot.
Water your plant stock well with tepid water the night before you take a cutting.
Take a 4-inch cutting from a firm, green stem. Cut the leaf stem close to the main stem of the cutting, leaving a stub so you don’t damage the node. Remove some of the larger leaves from the cutting. Do this early in the morning so the plant has had an opportunity to build up a reserve of water.
Dip the stem of the cutting into rooting hormone. You can use either a powder or a gel.
Plant the stem in the Rockwool cube, making sure the end doesn’t poke out of the bottom.
Fill a growing tray until level with perlite, vermiculite or potting soil and tap the tray gently to settle the growing mix.
Place the cube on the growing mix and water the planting mix around it to settle it. Add more growing mix if necessary.
Place a clear tray lids over the plants and place the tray on a heating pad set to 80 degrees Fahrenheit.
Crack the tray lid 1/4 inch the day the roots appear. Open the lid 1/2 inch the next day. Remove the lid after that and they are ready to transplant. Roots usually start to appear after 14 days.
How to Use Rockwool Cubes for Plants. In a process similar to that used to make cotton candy, basalt and chalk are spun into Rockwool, which is turned into cubes. Rockwool is a brand name; the generic term is rock wool. Rockwool cubes, 1 or 2 inches wide and 1 1/2 inch deep, are used for germinating seeds for …
Seedlings and Rockwool
Would this work if I germinated the seed in a paper towel, then placed it in rockwool, then (last) take the little rockwool plug and put it in a cup and placed clay pellets around it? Or would I need to rinse the rockwool off the plant?
Answer: Tim- whenever you start seeds using the wet paper towel method, you want to make sure you transfer the seedlings to their new growing medium as soon as they sprout (and before the tap root gets longer than about 1/2 an inch long). There is only so much energy available to the seedling inside the seed itself, and it takes an incredible amount of energy for the little seed to put down a tap root. If the seedlings are not placed into the new growing medium in a timely manner and given a little seed-starting fertilizer, your success rate will be horrible.
Using rockwool as the growing medium for the new seedling has its own issue. Rockwool is notorious for having an alkaline pH. This can cause problems in all kinds of plants. full grown, and especially little seedlings. I recommend Rapid Rooter plugs, but if you are set on tying out the rockwool just be sure to pre-soak it for several hours in pH adjusted water first- or make sure you purchase a rockwool product that HAS been pH adjusted. Otherwise, your success rates (again) will be horrible.
Finally, once a seedling has grown roots through a growing medium, you want to disturb those roots as little as possible. If your seedlings were grown in a rockwool plug, you should not attempt to remove any portion of the rockwool. Simply transplant the whole thing into the next container and, as you indicated, support the seedling by filling in the container around the seedling with pre-soaked clay pellets.
It is important to pre-soak clay pellets,for a minimum of 20 minutes, because they absorb water slowly (and than drain rather quickly). Using clay pellets that are not moist enough may prevent roots from growing down into the clay pellets, even with regular irrigation cycles after that point.
If you are using the loose kind of rockwool, than your transplant will be much the same as transplanting a seedling grown in soil. You may want to loosen the root zone gently before transplanting, to promote the spreading out of the roots. If some of the loose rockwool falls away from the root ball in the process that is OK, but do not try to pick around the roots removing additional rockwool- simply transplant the seedling into the new container and treat it the same as if you had used a rockwool plug. I hope this helps you out Tim, and Happy Growing!
Seedlings and Rockwool Would this work if I germinated the seed in a paper towel, then placed it in rockwool, then (last) take the little rockwool plug and put it in a cup and placed clay pellets