Story by Max Yields
The easiest way to germinate your seeds is to simply plant them in your growing medium. When container gardening, start by preparing the medium and the planters. Fill small pots or seedling trays and thoroughly moisten. Check the pH—it should be 5.5-6—and adjust if necessary. Poke the eraser end of a pencil 1/2-inch into the growing medium. Drop a seed into the hole and cover loosely. Do not pack it down.
Keep the surface moist, and in a week or two sprouts should start popping through. To prevent drying out, cover the planters with clear plastic and create a mini-greenhouse. This will keep the temperature and humidity a little higher and hasten germination. Don’t completely seal the planters up in plastic, because fresh air is required as well. Completely remove the plastic as soon as sprouting begins.

The procedure is much the same for hydroponic gardening in rockwool. However, you must prepare the rockwool before you plant. Begin by saturating and conditioning it to lower the pH. Start by soaking the cubes or slabs overnight in nutrient solution with a pH of 4.5. To lower the pH of the nutrient solution, use dilute solutions of calcium nitrate, nitric acid, sulfuric acid, or phosphoric acid. After soaking, the pH of the nutrient solution should be around 5.5. When using new rockwool, the pH of the nutrient solution may rise for the first few weeks, so keep a close eye on it. If it rises above 7, saturate the rockwool in a dilute phosphoric acid solution with a pH of 4.0 for 30 minutes, then flush. This will help neutralize the alkalinity and stabilize the rockwool. For best results, run the system and make adjustments until the pH is stable before you start the garden. When it’s ready, drop a seed down into the premade holes provided in the cubes or slabs. If there aren’t any, poke your own about 1/2-inch deep.

Some growers chose to germinate seeds before planting them. To do this, fold your seeds into a dampened washcloth on a plate. Cover loosely with plastic to retain moisture, and keep in a warm place. Keep the washcloth moist, and begin checking daily after the second or third day. When a seed breaks open, a small, white taproot will poke through. As soon as it does, plant it as described above with the taproot pointing down. Using this technique helps you isolate viable seeds from bad ones before you plant them, increasing your chances of getting them to sprout. This is especially useful when germinating seeds of unknown origin or questionable viability.

Germination rates are best at temperatures between 70° and 90°F. Unless the extra heat is necessary to keep the temperature up, lamps do not need to be on until the seedlings begin to sprout. This will also help the soil retain moisture. If cold is a problem, try placing a heating pad underneath the containers to warm the growing medium. Be careful not to overheat. Plant within two days after they begin to sprout.


Seedlings should remain in their starter pots or rockwool cubes until you begin to see roots poking through the bottom. When you do, it’s time to transplant. For container gardens, fill the larger containers with your growing medium and moisten thoroughly. Dig a hole out of the center just big enough for the root ball to fit into. Carefully remove the plant by rolling the container in your hands or gently tapping it on the sides to break it away from the root ball. Place your hand over the top of the pot with the stem of the plant between your middle and ring fingers. Tip it up until the root ball slides out of the pot into your hand. Place it into the hole you’ve prepared, and fill in around it. Try not to bury the stem. A thin layer of topsoil can be spread around, but not more than 1/4-inch. Tamp it down a little to secure the plant, but don’t pack it too tight or the roots will become root-bound and have difficulty growing out into the new soil.

Small rockwool cubes can be transplanted to larger slabs, a loose soilless mix, or right into soil. To transplant rockwool cubes into slabs, cut a square out of the slab with a razor or knife just big enough for the cube to sit in. Make it deep enough to set the cube about 3/4 of the way down into the slab. Some places sell precut slabs made to work with the cubes. Prepare the slab of rockwool for use as recommended and set the cubes into it, being careful not to damage the tender roots sticking out the bottom. To transplant into a container, prepare the loose growing medium, remove the plastic from the rockwool cube, and plant as you would a root ball. When transplanting rockwool cubes into soil, the smaller cubes work best.

Soil and rockwool have different water retention properties. As the soil dries, it will draw water away from the cubes. It’s important that some roots are growing out of the rockwool before you transplant, and that you keep the soil moist enough to hold water in the cubes until the roots can take hold.

At this point, you may want to add a little vitamin B1, Superthrive, Thrive Alive, or any of the other available vitamin and hormone additives to reduce the risk of shock and stress. Remove the plastic covering or humidity dome and/or the heating pad, and start up the growroom.