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 it difficult to over-water or under-water seedlings, making rockwool cubes suitable for both beginners and experts. Our rockwool cubes come with planting holes for seeds and are pre-scored for 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 without needing extra pebbles. They will provide a sturdy and solid foundation for your plants to grow.
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. But you can get really large cubes as well – cubes larger than 12” if you need them. Most often, the larger cubes are used to transplant smaller cubes into them. For example – you may start your seedling in a 1” cube, and instead of transferring it into a hydroponic system you prefer to transfer it to a larger cube. This will let the root system continue to grow to from a wider base for the plant.
Our cubes are a little bit bigger than standard at 1.75 inches. We like this larger size because they fit more snugly at the bottom of hydroponic net pots. If your cube is too small they can wobble around, creating an unstable base for your plant. In such cases you’ll need to add clay pebbles or coco coir around the cube to provide more stability. We like to err on the side of using cubes that are slightly too big, than too small – since you can always trim away some of the rockwool to get it down to size.
Rockwool Cubes for Hydroponics
As we know with hydroponics – soil is not used. So an alternative medium is required for plant roots to grow and to form the plant’s “root ball.” Soil alternatives must be porous for roots to grow and include coconut coir, tree bark, perlite, or even gravel. However - rockwool cubes, by far, are the most popular growing medium for plants in hydroponic systems. There are a few reasons 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.
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:
• They have a naturally high pH. 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.
• They're not bio-degradable. 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
• Step 2: Separate the cubes
• Step 3: Plant seeds
• Step 4: Sprinkle vermiculite into the planting holes and on top of the cubes
• Step 5: Maintain moisture and temperature levels
• Step 6: Move sprouted cubes under a germination light
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.
Rockwool's water retention and porous nature will increase your margin of error, for over-watering or under-watering. But it's not idiot-proof.
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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.
