How to use rockwool in hydroponics? 420 Guide for Beginners

Although growing hydroponically is soil-free, this doesn’t mean that there is nothing to support our plants.

In most hydroponic systems, growers use different types of hydroponic media to help support their roots and maintain a good water/oxygen ratio.

Growing in Rockwool: Tips from the Pros

Rockwool, also known as stone wool or mineral wool, is the most widely used substrate for the commercial production of hydroponic tomatoes. It is also a great tool for smaller growers who can benefit just as much from its use in a range of different systems and situations. While rockwool is relatively easy to set up and use, it does require some monitoring and irrigation adjustment to make the best of its ability to hold high levels of moisture and aeration at the same time.

Adjusting the pH Level
Depending on the brand of best rockwool cubes you purchase, the following instructions may vary. Adjust the pH of the water to 5.5 using pH down or lemon water if you have that on hand. Test and adjust pH as needed using a pH kit or meter. Soak the rockwool until the medium is fully saturated. Do not squeeze the block because the material has been designed for an optimal air/water ratio for horticulture purposes.

Planting the Seeds
Once your water is pH balanced, add your cubes and let them soak for about an hour, or until thoroughly wet.

Once your rockwool cubes are soaked, you’re ready to plant.  A smart tip for seed placement is to wet the tip of a toothpick and “pick up” one seed with the wet end. Place the seed at the bottom of the hole while gently pressing it to one side. If you are planting two seeds, press the second seed to the opposite side of the bottom of the hole.  Place your seeded rockwool cubes in a tray, and cover with the humidity dome to lock in moisture. You won’t have to mess with your cubes over the next 2-3 days.

Seeds that are grown in rockwool typically germinate fastest in a room temperature of 70 to 80 degrees Fahrenheit. Place the rockwool cube in a well-lit area or beneath a grow light for weed.

Add Your Vermiculite
Time to cover the seeds up with vermiculite. Just use a small pinch and sprinkle the vermiculite into each of the holes where your seeds are. Make sure you moisten the vermiculite to help it settle.

Set rockwool cubes on top of growing media. Cover nursery tray with a humidity dome to lock in moisture. Maintain close to 80°. Crack humidity dome when roots begin to emerge, gradually increasing the day after. Remove the humidity dome a couple of days after roots first appear. Transplant when roots begin to poke out the bottom of the cubes.

Best Rockwool Starter Plug for Sale

ECO Farm Rockwool Starter Plug





Maybe you are a novice grower, or maybe you are someone who wants to experiment with cutting edge growing products. Either way, all of our systems offer great ways to experiment and learn to grow like a pro. The Eco Farm Kits take the stress out of “what should I buy?” they give you everything you need to simplify the Eco Farm system. You choose to grow 4, 6, or 8 plants (or multiples of kits), making it easy to evolve and grow with your plant count.