Rockwool cubes are the ideal growing medium for hydroponic systems. Known for their excellent water retention, rockwool doesn't dry out easily, and its porous structure allows plant roots to grow freely. These qualities make rockwool cubes for hydroponics suitable for both beginners and experts, as they reduce the risk of over-watering or under-watering seedlings.
Our rockwool grow cubes come with pre-scored planting holes for seeds, ensuring easy separation. Measuring 1.75" x 1.75", they fit perfectly at the bottom of your net pot, providing a stable foundation for healthy plant growth. No extra pebbles are required—just the sturdy and solid foundation of rockwool cubes to support your plants from the start.
What are Rockwool Cubes?
Rockwool comes from volcanic rock which has been melted and spun into fibers, giving it it’s wooly texture. These sheets of rockwool are then scored into squares, which makes them easier to pull apart into the form of cubes… hence, rockwool cubes!
Scoring can be done at various sizes, with 1” to 1.5” cubes being the most common. However, larger rockwool grow cubes are also available – some even larger than 12” for specific needs. Larger cubes are often used to transplant smaller cubes into them. For example, you might start your seedling in a 1” cube, and instead of transferring it directly into a hydroponic system, you may prefer to transfer it into a larger cube. This allows the root system to develop more broadly, providing a stable foundation for plant growth.
Our rockwool cubes for hydroponics are slightly larger than standard, measuring 1.75 inches. We prefer this size because it fits more snugly at the bottom of hydroponic net pots. A cube that’s too small can wobble, creating an unstable base for your plant. In such cases, you might need to add clay pebbles or coco coir around the cube to enhance stability. We prefer to err on the side of using cubes that are slightly larger, as you can always trim the rockwool cubes down to size.
Rockwool Cubes for Hydroponics
As we know, in hydroponics, soil is not used. Instead, an alternative growing medium is needed for plant roots to grow and form a solid “root ball.” Soil alternatives must be porous to allow for root growth, and options include coconut coir, tree bark, perlite, or gravel. However, rockwool cubes are by far the most popular growing medium for plants in hydroponic systems. Here’s why:
• Easy Germination. These cubes are very easy to germinate with. Give them a good soak with water, drain for a few minutes, and plant your seeds. Most cubes come with a small pre-made hole, about 1/2" deep, where you can plant your seed. You can also poke your own hole with a small stick or skewer.
• Cubes keep their shape. When using coconut coir or gravel, it needs to be kept tightly packed or the medium can fall apart which damages the plant’s root system. But rockwool cubes keep their shape so it’s easy to move them around, and transfer them into your hydroponic system.
• Excellent water retention. Rockwool has outstanding water retention properties. They soak up water like a sponge but don’t dry out as quickly. They hold onto water for long periods of time so they’re hard to underwater. Since rockwool holds a good amount of oxygen between their fibers, they hard to over-water too. This makes rockwool very forgiving, making them great for beginners.
• Porous nature. Plant roots can easily grow in rockwool because of minute spaces in between the rockwool fibers. You’ll very often see healthy root structures finding their way out the bottom and sides of the cube.
• They are naturally sterile. Bacteria and viruses are killed during the heating process so rockwool is totally sterile after manufacturing. They will remain sterile as long as they’re not introduced to any new agents.
• Used the whole life of the plant. Your plant can grow in the same rockwool cube its whole life – from germination, all the way to harvest. There’s no need for your plant to be transferred to another medium.
Things to Keep in Mind When Using Rockwool Cubes
While rockwool is a fantastic growing medium for hydroponics, it’s not totally perfect either. Here are some things to keep in mind when using rockwool cubes:
- High pH Levels :- When soaking your rockwool cubes for germination, you can bring down the pH with some pH down. They can also raise the pH of the water in your hydroponic reservoir. Make sure to check and correct pH after transferring rockwool cubes to your hydroponic system.
- Non-Biodegradable: - Remember that rockwool is sourced from rocks! While rocks are naturally formed on Earth, they don’t break down very well. So when you throw them away in the trash, they’ll stay in the landfill indefinitely.
- Be careful with rockwool fibers: - Loose fibers can irritate your eyes, skin, and even be inhaled. Using a dust mask or medical mask over your nose and mouth can help prevent inhalation. For prolonged contact, you can use protective eyewear along with gloves or long sleeves to prevent skin irritation.
Germinating with Rockwool
As mentioned, one of the best things about rockwool is they are perfect for germination. Its porous nature makes it easy for roots to grow. Its excellent water retention helps seeds stay moist which is critical, since water activates the shell of the seed embryo which starts the germination process. And the fact that cubes hold their shape makes them easy to move around, and transfer to your hydroponic system when seedlings are ready.
Learning how to germinate is an important part of owning a hydroponic system. So important in fact – we have dedicated an entire section of our website, on seed germination with rockwool. But here is a quick over view of the process:
- Step 1: Soak Rockwool Cubes and Drain
Begin by soaking the rockwool cubes in water to ensure they are fully hydrated. After soaking for a few minutes, drain the excess water to ensure the cubes are moist but not soggy. - Step 2: Separate the Cubes
Gently separate the soaked cubes along the pre-scored lines. This allows you to prepare each cube individually for planting. The pre-made holes in the cubes will provide a convenient spot for planting seeds. - Step 3: Plant Seeds
Place your seeds into the holes provided in the rockwool cubes. Be sure to plant them at the recommended depth for your seed type. If needed, you can create your own hole with a stick or skewer. - Step 4: Sprinkle Vermiculite
Lightly sprinkle vermiculite into the planting holes and over the top of the cubes. Vermiculite helps retain moisture and creates a light, airy environment that encourages seed growth. - Step 5: Maintain Moisture and Temperature Levels
Ensure the rockwool cubes stay moist by regularly checking water levels and maintaining appropriate humidity and temperature. - Step 6: Move Sprouted Cubes Under a Germination Light
Once the seeds have sprouted and you see visible growth, move the rockwool cubes under a germination light or grow light. This provides the seedlings with the light they need to continue growing healthy and strong.
The germination section of our website will walk you through these steps in great detail. When your seedlings are ready to be transferred, our Starting Your Tower section will be handy for you to read as well.
Product Specifications:
- Dimensions: 1.75" length x 1.75" width x 1.5" height
- Weight: < 1 ounce per cube
FAQ
Rockwool cubes retain water well and allow roots to grow freely, making them perfect for hydroponics. Their porous structure also provides excellent aeration, ensuring a stable environment for plant roots to thrive.
Yes, rockwool water retention and porous nature increase your margin of error when it comes to over-watering or under-watering. However, it’s not completely foolproof—monitor moisture levels regularly.
Germinating seeds with rockwool cubes are simple. Soak the cubes, drain them, plant your seeds in the pre-made holes, sprinkle vermiculite on top, and maintain moisture and temperature levels. Once the seeds sprout, place them under a germination light.
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Awesome Cubes
These cubes originally came with my ALTO Garden tower. When planting my second season I bought some other cubes but they were smaller and didn't work as well. So bought these again and they are terrific. Best way I can describe them is "hearty." They are fuller and bigger and fit snug at the bottom of the net pot so my plants don't wobble around. Great cubes will stick to these from now on.
