How to Start Hydroponic Seeds


The agricultural system of hydroponics uses nutrient-rich water instead of soil to nurture plants. The plants are anchored using an inert growing medium such as rockwool, gravel or sand. Rockwool is spun lava rock manufactured into cubes. This provides a stable medium for seeds during the germination process and may be implemented directly into the hydroponic system of your choice when the seedling is ready to be moved.

Step 1

Select a warm, sunny area to set up a seed tray.

Step 2

Pour several seeds from the packet of the plant you intend to grow in a hydroponic system or systems. Start several different types of seeds at the same time, if you wish, as most trays have spaces for a number of cubes. Organize the seeds into groups of three.

Step 3

Saturate a rockwool cube in a small dish of water. Drop three seeds in the depression in the top of the cube. Place the cube in one of the niches of the seed tray.

Step 4

Continue seeding rockwool cubes with the seeds of your choice. Line up the cubes so that the seeds of each type of plant are separate.

Step 5

Place garden markers along the rows to indicate which type of seeds are in that row.

Step 6

Add a small amount of water to the tray, just enough to cover the bottom one-third of the rockwool cubes. Cover the tray with a plastic cover. Make a loose tent of plastic wrap if you don't have a plastic cover.

Step 7

Monitor the seeds each day. Add water to the tray as needed to keep the rockwool cubes moist. Check for signs of mildew or mold on the rockwool. Remove those cubes and replace with freshly seeded cubes. Shift the cover or plastic wrap to allow for more airflow over the seed tray.

Step 8

Thin the seedlings from each cube, leaving only the strongest to grow. Mix 1/2 tsp. of hydroponic nutrients to 1 gallon of water and add to the water supply when the seedlings are 1 to 2 inches tall.

Step 9

Remove the seedlings from the tray when they reach 3 to 4 inches tall. Add the seedlings to the hydroponic system.

Things You'll Need

  • Seeds of choice
  • Rockwool cubes
  • Seed tray with cover
  • Garden markers
  • Hydroponic nutrients


  • The Hydroponic Shop: How to Start Seedlings for Hydroponics
  • Planet Natural: Starting Seeds Indoors
  • Online Garden Tips: How to Start Seedling for Hydroponic

Who Can Help

  • Hydroponic Shop: Hydroponics Growing Media
Keywords: seedlings for hydroponics, seed starter tray, hydroponic seedling starter

About this Author

Shelly McRae resides in Phoenix, Ariz. Having earned her associate's degree from Glendale Community College with a major in graphic design and technical writing, she turned to online writing. Her credits include articles for, and several non-commercial sites. Her work background also includes experience in the home improvement industry and hydroponic gardening.