Starting seeds in Rockwool is a process that one needs to know the essential tips and tricks of germinating seeds in a hydroponic system and take care of the nutrients and air circulation because the medium is anything but the common soil.

Starting Seeds in Rockwool How To Grow Them Right


The seeds require the perfect conditions to grow into the plants in the given medium and these conditions need to be maintained throughout the process.

This can be a little tiresome if you are doing everything and still the seeds are not germinating to their full potential.

Fortunately, you can forget about that if you follow the complete guide on how to start seeds in Rockwool in this article. 

How To Successfully Enable Starting Seeds in Rockwool?

To enable starting seeds in the Rockwool medium, prepare and maintain the Rockwool grow cubes, sow in the seeds, maintain the conditions, and lastly, transfer the plantlets when they reach the height. As a result, it will show positive germination of the seeds. 

The medium is a moisture retention medium that offers great oxygen circulation and supports a hydroponic system for plant nutrition and growth. The best thing about this given medium is that it is also completely inert. It does not interact with any of the nutrients that are fed to the seeds through the water thus making it a very safe environment for the seed to grow. 

– Prepare the Rockwool Medium 

The forest step is to prepare the Rockwool medium according to the needs of your seeds. This is why you should remember that the medium is fairly basic with a pH of 7 to 8. This may be too basic for seeds that grow best in an acidic environment. For this purpose, we need to adjust the pH of the medium. 

Prepare the Rockwool Medium

The best way to do that is by soaking the medium in acidic water before you plant your seeds. The acidic water can be made by adding a few drops of lime juice or any other method that you prefer. The soil’s acidity level will change very quickly, this is why you should keep checking it. Any pH from 5 to 6 will be perfect for an acidic environment if of course the subject benign planted requires this. 

Once your medium has reached that level, you can now move forward to sowing the seeds. Keep in mind that you do not need to adjust the pH for each seed, but only for those who require a slightly acidic environment. One of the best-known Rockwool cubes is the Grodan starter mini-blocks

However, if you are new to hydroponic farming and Rockwool, things can get out of hand and run a little dry if not taken care of. For this reason, it is very important to follow the correct ways for healthy and nourished plants in rockwool or any other medium that is dry or too moist.

– Plant the Seeds

The second step is to plant the seeds in the pH-optimized Rockwool medium, and now, take two seeds and plant them in a hole in the medium. You can use a blunt object to press the seeds to the bottom or the middle of the Rockwool medium. 

After sowing the seeds, transfer the Rockwool cubes onto a tray and cover it with a humidity dome for retention of any and all moisture in the medium. Now, they will try to sprout, and this is where the moisture will play its part, and when this step is done properly, your plant will find itself in the right environment to establish. 

– Maintain the Conditions 

After successfully sowing the seeds in the medium and covering the tray with the humidity dome, it is now the game of maintaining optimized conditions. These conditions may vary depending upon the location, outside and inside weather, type of seeds, type of the applied hydroponic system, and lastly, the generics of your unique gardening ways. 

Maintain the Conditions

If you consider, you will see that that is a lot to ponder, but don’t worry because this is how the seeds will germinate to their full potential, and show you a good thrive. The commonly set temperature for Rockwool medium is 70 to 80 degrees Fahrenheit. 

Remember that you need to maintain the moisture content of the medium. It should feel moist to the touch, so it is important to water it every couple of days sparingly or use a spray bottle when they seem to get a little dry, but of course, not in a prolonged matter. Keep in mind that these signified cubes should not be bone dry. As a result, you need to maintain the conditions of temperature and moisture for the time until the seeds start sprouting. 

When you see them sporting, remove the humidity dome and immediately move them under a light source. You will now need to keep them under the light until the sprouts grow in height. 

– Transplant Plantlets 

You should check and see it grow until it reaches a height of two to three inches; then you must transplant the plantlets into a separate pot or wherever you see fit.

Make sure that you maintain the conditions for the newly transplanted plantlets as well. 

How To Safely Use Rockwool Medium?

You can safely use Rockwool medium by wearing protective gear taking notes and preventing any cross-contamination, and finally, disposing of the used Rockwool material properly, so that the medium is kept clean and would not harm any of the surroundings.

– Use Protective Gear

The Rockwool material can cause allergic reactions on the skin and can make it irritated. This is why wearing protective gear before handling these cubes and materials is highly advised, because of different reasons such as transporting bacteria. Gloves, eye goggles, and a mask should work just fine; you should also wear full clothes covering your arms and legs, for extra protection from the pollution around you and on you.

Use Rockwool Protective Gear


Some people might be more at risk of allergies through the Rockwool material than others. Look for common signs of allergy and infections when you first come in contact with the material. If you find yourself sneezing and your breathing feels disrupted, these may be the signs that you are allergic to this material, which is why taking measures is a better choice. 

– Prevent Cross-Contamination

Cross-contamination is very common in a hydroponic system, so while dealing with this wool that is dense in its moisture levels, in such systems, make sure to keep a strict eye on the tools and materials used for various plants in the same system.

Once cross-contamination occurs, it can be very hard for you to contain the system. 

– Dispose of Rockwool Material 

As the Rockwool material is not biodegradable, make sure to dispose of the used material carefully. You can either reuse it for some different purpose or combust it in a controlled manner. Make sure that you keep it away from people who may be at risk of infections or irritations on the skin. 

Dispose of Rockwool Material

The material has a high pH and also is non-sustainable over a long period of time so wherever you choose to dispose of it, make sure that the fill will be suitable for it. If you dispose of the wet cube, there is a very high chance that algae, bacteria, and fungi will grow in it. As a result, you should make sure to dry the material before you dispose of it completely. 


1. Why Are My Seeds Not Sprouting in Rockwool?

The main reason behind seeds not sprouting in Rockwool is that there might be less or no moisture in the medium for the seed. This is very common while operating with Rockwool medium as it requires moisture and nutrients from outside to germinate the seed as it is inert. 

The Rockwool medium works best with a hydroponic system as the medium itself has or adds no nutritional value to the system. It is therefore very important to keep the moisture and the nutrition level at an optimal level inside the medium. If it is not maintained, the seeds may not sprout at all and die altogether. 

2. Can I Reuse the Rockwool Medium?

Yes, you can reuse the Rockwell medium for up to six different crops after which it may lose shape. The reason behind its reusing is that the medium is made of inert fibers, so it does not react with any solution and thus can retain its structural integrity. 

The Rockwell medium is thus a reusable medium, but unfortunately, it is not biodegradable or sustainable. Because of this, it is important that the medium is used and reused until it cannot be anymore. Even though nothing will happen to the fibers, the main selling point of the medium is the structure and shape of the medium cubes that house the seeds perfectly. So if they are ruined, the medium becomes useless for further seeds.

3. Can Soil and Rockwool Medium Be Used Together?

Yes, soil and Rockwool medium can be used together in a single pot to germinate seeds. This is because both the mediums are ultimately there to germinate the seeds positively and for the plant’s growth so that both materials will add to the plant’s overall health. 

Soil can also be used to fill up any pot with Rockwool material and in the same way, Rockwool can be used to fill up any pot with soil in it. Till now, no negative impacts have been seen of using the two materials together and in theory, there shouldn’t be even. 


In this article, we talked about how you can start planting seeds in Rockwool medium, what are the dos and don’ts of the process, and also the pros and cons of starting seeds in this medium, but in case you missed something; here is a short review:

  • The main steps in starting the seeds in Rockwool medium are first to prepare and maintain the cubes, sow in the seeds, maintain the conditions, and lastly, transfer the plantlets when they reach the height.
  • The fibers of this medium may cause skin irritation so always wear protective gear while handling them and maintaining sanitary conditions as well.
  • The Rockwool medium, made of chalk and basalt rock, is an excellent medium for seed germination because of its various high-standing abilities and characteristics.
  • Due to constant moisture retention, the Rockwell medium may grow algae on the surface. Which is why you should dry it and then dispose it.
  • The Rockwell material is not biodegradable or sustainable for a longer period of time but can be used for up to six different seed cycles or crops.

Here we come to the end of the article. We hope the article was very informative and helpful for your hydroponic plantations using Rockwool medium. Happy gardening!

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