Rockwool Cubes

The original hydroponic growing medium and still one of the most widely used in in both small all the way to commercial applications. Rockwool blocks are an inexpensive and mess-free solution for a variety of systems and setups and the perfect growing medium for NFT systems. They are an inert substrate with great water and air holding properties which allow you full control over your plants nutrition, whilst giving you strong, fast root growth.

We offer rockwool cubes in 3, 4 or 6 inch square sizes, with either small or large holes. The smaller size hole is used to transplant the 25mm Rockwool Propagation Cubes and the larger size hole is used for all of our other propagation mediums; 36mm Rockwool Propagation Cubes, Jiffys, Eazy Plugs and Root Riots. 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.

Using rockwool as a hydroponic substrate gives you fantastic advantages over traditional growing media for your indoor garden. Firstly, the water holding capacity is much greater, meaning litre for litre it can hold substantially more water than coco coir or soil. It also releases this water much easier than soil or coco does, meaning the plant does not 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!

As rockwool is inert and contains no nutrients you have complete control over what your plants are fed. This also means that you need to be a little more careful with your pH and EC levels as whatever you give your plants is what they will get! There is no buffer or ‘forgiveness’ you would get from soil or coco. Fortunately you can also monitor these levels with far greater accuracy than with other mediums. Being a stable and inert substrate the EC and pH level found in your hydroponic system tank will also be that which is in the rockwool block. Some people even choose to stick a syringe into the block itself and extract a sample of water! It is that easy!

How To Use Rockwool Cubes

Rockwool needs a little preparation before use. All you need to do is soak them in a low pH (pH 4.5-5) solution, some growers choose to do this for up to 24 hours but many will do a quicker soak. This is to neutralise the residual lime from the manufacturing process and ensure you start off with a stable and natural pH level for growing in. After this pH bath, you can soak them again in some premixed nutrient solution to your required EC and pH levels if desired and you are good to go! Remember 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 potentially ruin its performance. Leave them to drain naturally but if you are in a hurry you can gently whip/flick them to remove the excess water. Aim to reduce the water content by roughly 25% for best results.

As with all cases of transplanting, it is important to ensure your plants are well rooted for best results and this is especially true with rockwool. An inadequate root system before moving into a hydroponic system is sure-fire way to failure. We recommend rooting your plants outside of your system and hand-watering or using an irrigation system initially. A simple setup involving either a Garland Tray or saucers lined with some clay pebbles to stop the cubes from sitting in water works a treat. Be sure to leave the plastic sleeves on the blocks during this stage to help prevent light getting to the roots and to promote them to grow downwards, but remember to remove them when you plant out! Don't forget that rockwool hold water very well, make sure you have adequate air between the blocks when rooting and take caution to no overwater them. If moving to an NFT system then pay attention that the blocks are placed the right way round, underneath you will notice ‘channels’ running along them. These should be positioned in the same way as the water is flowing on your system.

Rockwool cubes are available in 3", 4" and 6" sizes with large and small hole options.