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You’ll be most familiar with rockwool as a loft insulator - the itchy, lightweight yellow/orange stuff in your loft - making use of the thermal insulating properties of the substrate. Rockwool is also perfect for hydroponic substrate applications since its inert so doesn't have any nutritional content of it’s own so what you choose to feed in your nutrient solution will be the only source of plant food, allowing the gardener more precise control. Rockwool has good drainage properties; retaining the perfect ratio of air and water to support root growth which sets the perfect scenario for spectacular growth above ground. Rockwool, as a hydroponic substrate for plants, can come in many shapes and sizes from small cubes for rooting cuttings to large blocks for flowering plants that can support a large, heavy crop. For more info on Rockwool, the different types and how to use it in your environment, read our buyers guide below.

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  1. Rockwool Cubes

    As low as £2.50
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    As low as £2.95
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Buyer's Guide


Rockwool has proved itself to be a superb hydroponic medium, providing the perfect mix of aeration and nutrient solution for plant roots to uptake precisely what they need as and when it's required. You can use rockwool in a number of systems, showing its versatility - from drippers to NFT, Rockwool is implemented in many systems with success across the board.

When choosing your final block size, bear in mind that smaller blocks like the 3” are more space efficient whilst larger blocks are more forgiving with less maintenance required as they will hold more moisture. Small blocks require more regular irrigation while larger blocks will require less frequent watering - The size of the plants will also determine how regularly you’ll need to feed - you’ll need to match your duration and frequency of feeds to the uptake of the plant. Don't ever let rockwool sit in it’s runoff water and never let them completely dry out.

Providing you don’t let your rockwool sit in runoff, it’s almost impossible to overwater, as excess solution just drains out the bottom.

We source our Rockwool products from Cultilene as we find their products to be extremely reliable and consistent across batches meaning you’ll get uniform crops across cycles as long as all other environmental factors remain the same.

Despite Rockwool being inert, Beneficial microorganisms can thrive in the substrate, especially once plants have colonized the media and release root exudates that feed the friendly organisms. Use a product that contain mycorrhizae or trichoderma to see your root mass explode!

Unlike soil or coco, Rockwool contains no macro or micro nutrients so you’ll need to get a good range of nutrients to make sure that the plant has everything it requires. A good quality range should contain everything a plant need during it various growth stages just remember that different varieties of plants can cope with different nutritional levels so you’ll have to experiment with what's best for your plant type in your system - we recommend starting at ¼ or ½ strength of the feeding chart and only increasing your dose once you’re certain the plants won’t burn.

When using rockwool as a substrate for plants you need to soak them to stabilize the pH of the block since rockwool can be too alkaline for some species - we recommend soaking your rockwool for 24hrs in pH treated water before any plants have been introduced.

It’s also recommended to use plant support when using rockwool as a substrate since plants can become top-heavy when the blocks get dry. Use Scrog nets or circular trellis to ensure your plants don’t fall over when they get heavy from the sheer weight of the crop.

If you’ve got more questions about how to implement Rockwool in a hydroponic garden or if you’re unsure if the substrate is right for you, get in touch with our specialist team on 0800 085 7995 or email us, as we can advise you on the applications of Rockwool within a horticultural environment.