Grodan Rockwool Cubes




  • Perfect for potting on young seedlings and cuttings
  • Brand leader in rockwool production
  • Grow like the pro’s!
  • No mess!
  • Inexpensive.
  • Homogenously manufactured

It really is hard to beat the sort of rapid growth and (ultimately) high yields that you can achieve when using Grodan ‘rockwool’ as your hydroponic growing media. They give you, the grower, ultimate control over the nutrient content, pH levels and moisture content throughout every stage of your grow. This sort of control is mastered in commercial hydroponic greenhouses throughout the entire world, ensuring they get the maximum possible yield, every time! Why settle for anything less?

Grodan have been developing rockwool for many years and have an extensive manufacturing process that ensure you receive the finest quality of rockwool substrate, every time you buy. Grodan are a cornerstone of the commercial hydroponic sector, you will struggle to find a better product on the market!

These blocks come in either 3 or 4 inch square versions, with either small or large holes in to cater for all types of plugs. The size of block you need sometimes does not necessarily make a significant difference, but there are of course more suitable applications than others depending on the system that you are using. Please feel free to give us a call to see what would be most appropriate for you.


Grodan stonewall blocks are made from natural mineral ingredients, primarily basalt volcanic rock. The material is then heated up to extremely high temperatures, 1600°C. The heated mas is then spun in several directions until a candyfloss like texture has been achieved. This process gives Grodan rockwool blocks unique properties for growing hydroponically that give fantastic advantages over traditional gardening substrates.


Using stonewall as a hydroponic substrate gives you fantastic advantages over traditional growing media for your indoor garden. Specifically, these advantages relate to its water holding properties and E.C/pH control.


Firstly, the water holding capacity is much greater, meaning litre for litre it can hold substantially more water than coco coir or soil. Secondly it releases this water much easier than soil or coco does, so the plant doesn’t use as much energy obtaining the water from the substrate. This means you can use a lot smaller volume of media, and your plant has more energy available for vegetative or generative growth above ground. Maximum efficiency in almost every way!


You can monitor and control the EC and pH of rockwool to a much more precise degree than any other substrate can offer. A plant’s requirement for nutrient changes throughout its entire life cycle and rockwool allows you to respond to these changes almost instantly. This means you can maximise your plants’ performance at every key stage and really push the limits of your potential yield. Monitoring what is happening within the rootzone is obviously key to this. With Grodan rockwool blocks, you are able to take a sample of the solution in the rockwool directly rather than relying on run-off from a previous irrigation. Simply stick a syringe in the slab and extract the water within!


Before you begin using these blocks in your hydroponic grow tent, you need to quickly treat them to ensure your plants start with explosive growth! All you need to do is soak the rockwool blocks in a low pH (pH 4.5-5) solution. This is to neutralise the residual lime from the manufacturing process and ensure your start off with a more stable and natural pH level for growing in. After this quick pH bath, soak them again in some premixed nutrient solution to your required EC and pH levels and you are good to go!

After you have soaked your cubes, they will be heavily saturated with water. You need to drain some of this water so you do not overwhelm a young root system when you transplant. Do not be tempted to squeeze the water out of the blocks. This will damage the fibrous structure of the block and ruin its potential performance. Instead you will need to give the blocks a gentle whip or flick to get the excess water out. Aim to reduce the water content by roughly 20% after soaking.

Try to ensure that you air prune the blocks before they are transplanted on to their final irrigation system. This requires keeping the blocks off of a flat surface to ensure a layer of air surrounds the entire block. Use a wire or plastic mesh to stand the blocks on rather than placing straight onto a plastic tray. This will ensure a larger root mass is produced inside the block and it will not be as easily effected by transplant shock, hindering its growth.


Although beneficial bacterial /fungal products can be used (to a degree) with Grodan blocks, it is often best practice to keep the entire system as sterile as possible.

Feel the weight of each block after each irrigation. As a general rule do not irrigate again until it feels at least 50% of its starting weight.

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Grodan Rockwool Cubes

Grodan Rockwool Cubes