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How to Start Seeds for Hydroponic Systems

Updated on June 5, 2014

Hydroponics is the practice of growing plants in nutrient enriched water rather than soil. The plants are placed in a hydroponic system which delivers the nutrients directly to the roots, using water as the medium.

In hydroponics, an inert medium, such as clay pellets anchors the plants in net pots, and these cage-like pots hold the plants and pellets in place within the hydroponic system.

For soil gardeners, seedlings are available at garden centers, ready for planting. You can remove the soil from seedlings and add them to the hydroponic system, or you can start seeds hydroponically.

Seeds and seedling in rockwool cubes
Seeds and seedling in rockwool cubes | Source
Seedling in net pot installed in hydroponic system
Seedling in net pot installed in hydroponic system | Source
Lettuce raft hydroponic system
Lettuce raft hydroponic system | Source

Setting up the rockwool cubes
Rockwool cubes are made from spun volcanic rock, and works well for starting seeds because the cubes retain moisture. Rockwool has a high pH, though, so before placing your seeds in the cubes to germinate, rinse the cubes with a vinegar and water solution to neutralize the pH balance. Mix one teaspoon of vinegar to half a cup of water and just dip the cubes into the solution and shake off the excess.

Add about one inch of tap water to a small container and place the rockwool cubes in the container. (I use the plastic food storage containers you can find in the supermarket: 3-in by 5-in and 3 inches deep) The cubes have a small depression in the center at the top; this is where you place the seeds.

The rockwool acts as a wick and pulls the water into it, so the seeds have a moist environment. If the cubes are too wet, keep a little less water in the container.

The seeds germinate in rockwool in about the same amount of time as they would in a seed starter soil mix.

Locate your container where it receives filtered light. Place the container on a table or windowsill that receives partial sunlight -either morning light or afternoon light- if you germinate your seeds indoors.

For outdoor locations, choose a partially sunny location, such as a patio or porch. Ensure the container is protected against high winds or rainfall as well. Because the container is small, it is portable, so you can move it indoors should you need to protect it against bad weather.

There are several types of hydroponic systems. If you're new to hydroponics, the lettuce raft system is easy to build; watch the video for instructions. Select greens, lettuces and herbs as an introduction to starting seeds hydroponically, and use your lettuce raft. Try this system indoors for fresh greens all year round.

Add water to the container only when you see the cubes getting dry. Too much moisture increases the risk of mold developing on the rockwool. If the cubes are too dry, the seeds won't germinate. You want the cubes moist, but not wet.

Add 2-to-3 drops of liquid nutrient to the water in the container when the seedlings are approximately 2 inches in height. This gives the seedlings a nutrient boost that encourages root growth.

Transfer to a hydroponic system
Prepare the seedlings for transfer to the hydroponic system when they reach approximately 3-to-4 inches in height. Fill a net pot approximately 1/2 way with clay pellets. Place the seedling, nestled securely in the rockwool cube, in the center of the net pot. Fill in around the seedling with clay pellets to fill the net pot. Install the potted seedlings into the hydroponic system.


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    • Shelly McRae profile image

      Shelly McRae 6 years ago from Phoenix, Arizona

      Thanks, Donna. Hydroponics is an interesting method for growing plants, and my DH and I hope to add a hydroponic garden to our front porch soon. Thanks for stopping by.

    • DonnaCosmato profile image

      Donna Cosmato 6 years ago from USA

      Extremely informative but simple to understand. Like Rebecca, I've always been fascinated by the concept of hydroponics but never really understood it. Voted up and shared!

    • Shelly McRae profile image

      Shelly McRae 6 years ago from Phoenix, Arizona

      It's really simple to do, and this is just one method. Thanks for stopping by, Rebecca.

    • Rebecca Scudder profile image

      Rebecca Scudder 6 years ago from Upstate New York

      This is great! I always wondered how seeds were started for hydroponics- I didn't understand why they didn't just wash away.