How to Plant in Rock Wool Cubes

Fill a bucket or other large container with water and adjust the pH of the water to 5.5, using pH down. Test the pH with a meter or pH test strip to make sure the pH is at or just above 5.5, no lower.

Soak the rock wool cubes in the water for at least 30 minutes.

Make a starter fertilizer solution, diluting liquid fertilizer or hydroponic nutrients to one-quarter the normal recommended strength. You can either make the solution according to package directions, diluting it with 3 parts water, or you can use only one-quarter of the recommended amount of fertilizer with the full amount of water. Adjust the nutrient solution pH as recommended on the packaging or for your plant.

Drain the cubes and flush them with your starter fertilizer solution, allowing the solution to drain to waste.

Plant one or two seeds in the hole of each rock wool cube. Pull the rock wool loose at the top of the hole to cover the seed lightly. Place the cubes into the hydroponic system or into a tray with drainage holes.

Place the rockw ool cubes in a warm environment with available sunlight or supplemental lighting.

Water the cubes three times a day with the starter fertilizer solution until the plants are large enough to transplant into your regular hydroponic system or in the garden. Make sure the plants have good drainage. The cubes should stay moist but not soggy.

Make a new fertilizer solution each week, increasing the strength of the fertilizer until the plants are doing well on full-strength nutrients.