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How To Start Seeds In Rockwool? A 7 Steps Comprehensive Guide!

The majority of people who attempt to start a tiny garden have little success the first year. There are a variety of challenges that arise that we wouldn’t imagine to be a concern.

The majority of these problems begin at the germination table. It takes some practice to figure out when to turn on the humidity dome, how much to water, and how often to water.

We’ve all returned home to see seedlings that have dried out and died. We’ve all accidentally killed transplants by not being kind enough.

As we try new things over time, the answers become second nature. Rockwool is one of those growing media that, once discovered and used a few times. This article is a complete step-by-step guide on how to start seeds in Rockwool.

How To Start Seeds In Rockwool
via Reddit

Molten basalt rock is combined with a limestone addition to make Rockwool. The liquid rock and limestone mixture is poured into a machine that spins it into sterile inert superfine fibers.

Rockwool is made up of 37 cubic feet of rock for every cubic foot of the rock. The ability to grow more in less space is the most major advantage of Rockwool over potting soil.

Plants in the soil must expend energy to grow long enough roots to reach the nutrients they require to survive. In Rockwool, plant roots have immediate access to water and nutrients.

As a result, instead of root formation, the plant focuses its energy on growing taller and stronger.

Things You’ll Need

The physical nature of Rockwool could irritate your skin or eyes. Therefore, you’ll need:

  • Gloves
  • Dust Mask
  • Goggles
  • Rockwool
  • Water
  • Tray
  • Plastic Wrap
  • Toothpicks

How To Start Seeds In Rockwool?

  1. Fill a jar halfway with water with a pH of 5.5.
  2. If your Rockwool cube has a plastic wrap around it, using toothpicks punch small holes in the base to allow excess water to drain.
  3. Soak the Rockwool in water for at least one to two hours to allow it to absorb all of the liquid.
  4. To release excess moisture, remove the Rockwool and shake it. Squeezing the material compresses the fibers and eliminates the material’s inherent aeration qualities.
  5. The majority of Rockwool has perforations at the top. One seed should be placed in each opening and gently pushed down.
  6. In a tray with sufficient drainage, place the Rockwool. Rockwool cube and tray sets eliminate the guesswork from this stage. Place the tray in a room with a temperature of 70-80 degrees Fahrenheit. Set the tray in natural sunshine or under to grow lights.
  7. Mist the Rockwool and cover the tray with a plastic dome to keep it moist.


  • It’s now time to let it live and grow! In around 3 days, your seeds will begin to sprout, and in a few more days, you will see your first genuine leaves.
  • If you choose to plant two seeds per cube to increase your germination rate, now is the time to snip the tips off the seed that isn’t the strongest (or tallest) in each cube.
  • Pulling them out will disrupt the strong plant that shares the cube with you.
  • Maintain a close check on your plants and cubes.
  • Feel the cubes now and then, and if they appear to be drying out, spray pH-balanced water directly onto the cubes.


You’ll be able to transplant your crop to your hydroponic system a few weeks following germination.

1. Safety Measures

  • Keep an eye on your cubes around this time because the best moment to transplant is when the roots start to emerge from the bottom of the Rockwool cube.
  • This will ensure that the roots of the plant grow lower into your system.
  • If you wait too long to transplant, the roots will wrap around the bottom of the cube, preventing it from expanding.

2. How to Transplant

  • Cut the seeds apart after the first set of leaves has fully opened when planting them in Rockwool. While the seedlings are still in the Rockwool medium, you can transplant them into individual pots filled with regular potting soil.
  • When the root system of Rockwool seedlings begins to break free from the starter block, you know it’s time to transfer them.
  • If the weather permits, you can transplant these blocks directly into your garden, or you can keep them in containers with soil until the season is ripe.
  • You can even place the seedling inside a larger block of Rockwool to continue hydroponically growing the plant. Cut a hole in a four-inch Rockwool block the size of the seedling block and set the seedling inside. That’s all there is to it!

>> Related Post: The 8 Step Guide On How To Transplant Aerogarden Plants

Benefits of Starting Seeds in Rockwool

Here are some of the advantages of utilizing a Rockwool cube to germinate seeds.

1. Water Retention

Rockwool cubes offer high water retention properties, which is critical for seed germination. Rockwool, on the other hand, will not clog your system. It can remove extra water while maintaining just the correct quantity of moisture for your seedlings to germinate.

2. Air Circulation

The root system will benefit from good air circulation and oxygenation thanks to the Rockwool cubes.

3. Clean

Rockwool is a sterile or clean medium that is free of weeds, diseases, and pests.

4. Reusable

Rockwool cubes are reusable since they do not disintegrate over time. As a result, it can be reused multiple times.

5. Safety

They’re safe because they’re constructed of natural materials. As a result, it is extremely safe to use for germinating seeds because it contains no hazardous elements.

How To Provide Proper Care For Seedlings In Rockwool

Your seedlings will not get any natural nutrients from Rockwool. Gardeners will appreciate this feature since it allows them to treat their plants with the necessary nutrients for maximum plant growth.

While caring for seedlings in Rockwool, add fertilizer to the misting water. Because the plants readily absorb the nutrients, you don’t need as much as you would when planting seedlings in soil.

At first, keeping an eye on the moisture level in the Rockwool seems difficult because you don’t want the material to dry up and kill your seedlings. You gradually gain an understanding of how the material behaves in your home’s surroundings.

Final Remarks

The seed starts to benefit greatly from the use of Rockwool cubes. They’re safe, and they’ll keep your seed moist and oxygenated for optimum germination.

They are available in various sizes and forms, and they can be used in a variety of growing systems. As a result, use Rockwool to offer your seeds a better chance of germination.

Growing plants from seeds shouldn’t be intimidating if you have a lot of experience with different mediums. If you know how to start seeds in Rockwool, you won’t have to worry about poor moisture availability or unstable circumstances affecting germination.

The idea is to start by regulating the pH level of the cubes and then placing them in the greenhouse to induce sprouting.

You’ll find Rockwool to be a fairly forgiving substrate once you’ve become used to it as a growing media. You enjoy how the material makes it easy for plants to develop strong and quickly by supplying water and nutrients directly to their roots.

Rockwool is beneficial for growers like us who use it to start seedlings for transplant into outdoor gardens. It’s great for full-hydroponic home gardening systems.

I hope you find this instruction to utilize Rockwool to start seeds useful. Consider comparing Rockwool to soil in your next seedling crop to determine if you, too, are a Rockwool convert.