How to Germinate Seeds in Rockwool for the Tower Garden

Download the PDF version of Tower Garden Seed Germination Procedure.

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This seed germination procedure has been adapted from a procedure shared by Joe of Level 2 Concepts. It’s a little different than what’s in the Tower Garden manual, but works well at home and in a school classroom.

If you need supplies, another Tower Garden, or help with the Tower Garden you have, please email me at steve@keepitwatered.com. I’ve been supporting teachers and individuals who use Tower Gardens since 2015.

The yellow cubes in the photos are 3D printed. The .STL file is available for free download on the Tower Garden curriculum page.

Here’s a brief summary of how to germinate seeds in rockwool

Cut the rockwool apart.
Soak the rockwool in non-softened water for 30 minutes
Place the rockwool into the seed starting tray.
Place 8-10 lettuce seeds into the hole in the rockwool (Do NOT put in the vermiculite)
Put 1/4″ of water in the bottom of the seedling tray. (Just enough to cover the bottom of the seedling tray.)
Place the seedling tray in a dark place. A cabinet works well.
Check the seedlings once a day and put more water in to bring the level up to 1/4″ of water
For most lettuces, after just a couple of days, you should see a white fuzz on the seeds. (See photo below)
When you see the white fuzz, place the seedlings on the Tower Garden base with the lights turned on and as close to the tray as you can.
Rotate the tray each day and top off the water to 1/4″. In about a week, or when roots start to come out the bottom, it’s time to put them in the Tower Garden.

Soak the Rockwool for at least 30 minutes

Tower Garden Seed Starting Procedure Add Water

Use the pH test kit that comes with the Tower Garden. Put 5 ml of water in the vial and add 5 drops of the solution. Compare the color with the colored dots on the test paper. For a small amount of water, like the apple juice container in the picture, use just a few ml of the pH – or pH + at a time to adjust the pH. Don’t stress out if you can’t get the pH exactly right. Most plants will do fine if the pH is close.

Drain the Water

After about 30 minutes drain the water from the container. Be careful not to crush the rockwool.

Pour Seeds into Your Hand

Tower Garden Seed Starting Procedure. Place seeds in your hand.

You can tap the seed packet to plant the seeds, but I usually just pour some into my hand. It’s easier to not get too many seeds into the rockwool. Drop 6-10 seeds into the rockwool for lettuce. Generally, the larger the seed, the lower number of seeds to plant.

Help Kids Plant

Tower Garden Seed Starting Procedure Getting kids involved.

Kids will have an easier time planting if you pour a few seeds out onto a 3×5 card. Then ask the kids to count out 10 seeds and drop them into the hole in the rockwool.

Gather up the rockwool cubes and place them back into the container. Add about 1/4″ of water to the bottom of the tray. You want the rockwool to stay moist until the next day, but not soaking wet. Cover the container or place inside a dark cabinet so that all the seeds are in the dark. (A file folder works well for this.) Place the container on a counter or in a cabinet.

Check each morning and evening for seeds that have sprouted. Replace the water each day. Most lettuce will only take two days to sprout.

Sprouted Seeds

Tower Garden Seed Starting Procedure Seeds have sprouted

You’ll see what fuzz on the seeds when they’ve sprouted. Many people will wait too long to uncover their seedlings and they’ll be leggy. It’s important to uncover the seeds when they sprout and place them in good light. The Tower Garden base with the lights on could work for this or a clip-on desk lamp with a 6,500 K bulb. Replace the water each day with just 1/4 inch of water.

Ready for the Tower Garden

Tower Garden Seed Starting Procedure Seeds ready to move into the Tower Garden.

In about a week, your seedlings should be ready to put into the Tower Garden. Often times I’ll tell teachers to plant lettuce on Monday. By Friday the seedlings should be big enough to place in the Tower Garden for the weekend. If you want to grow better seedlings, wait until you see roots coming out the bottom of the rockwool before you put them into the Tower Garden.

Tower Garden School Purchase Information

What Seeds are Best in a Tower Garden?

Tower Garden Support