How to Germinate Seeds Using Rockwool

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While we recommend that beginner gardeners plant their first Vertical Organic Garden using fruit and veggie starters, you can also germinate seeds using rockwool! Both seeds and rockwool are included in your V.O.G. Starter Kit! This is a simple overview of rockwool and the germination process, full of tips and tricks to ensure your garden has the best start possible!


So what is Rockwool?

Originally used to insulate houses, rockwool is formed by melting rock and sand, and spinning the mixture into fibers, which are then formed into different shapes (usually cubes). The process of making rockwool is very similar to how cotton candy is made!

Rockwool is an excellent medium for growing because it not only holds lots and lots of water, but it’s fibrous texture also holds at least 18% air at all times. This is very helpful because seeds need plenty of water and oxygen to sprout!

Because rockwool is made primarily with limestone, it naturally has quite a high pH – about 8 – meaning it requires a little bit of prep work before you plant your seeds.


How to Prepare Rockwool for Planting:

  1. Fill a bowl full of water, and use your pH kit to adjust the water to a pH of about 5.5. Place the rockwool cubes into the bowl of water and let it soak for at least half an hour (up to two hours).

  2. While the Rockwool is soaking, fill a second bowl of water, add a splash of your vegan, organic fertilizer (about 560 parts per million), and adjust the pH to 5.5.

  3. Pour away the water that the rockwool is soaking in, and rinse through with the water/fertilizer mixture.

  4. Pull out the individual cubes of rockwool, and place them onto your germination tray, giving each cube a little shake to rid it of excess water. Do not squeeze the cubes of rockwool as you will damage the structure and destroy its ability to hold air and water!

  5. When all the rockwool cubes are laid out on the tray, you can widen the seed holes if necessary, using a chopstick or wooden skewer.

  6. Place your seeds into the cubes of rockwool. For the smaller seeds like lettuce and spinach, you can put a small sprinkling of seeds onto each cube. For larger seeds like beans, only one seed per cube is needed. Remember to prepare extra seed cubes, as not all of the seeds will germinate!

  7. Place the tray of seeded rockwool under a grow light, or in a sunny windowsill. After 2-3 days your sprouts will be ready for transfer into your Vertical Organic Garden!