These 1m long rockwool slabs by Grodan holds lots of air and water meaning fast rooting and therefore growth. The long slab means several plants can be grown together thereby reducing delivery and draining pipework. The nutrient solution is pumped to the plants via drippers and excess nutrient solution drains out of the rockwool slabs. These can be used in re-circulating o run-to-waster systems and are a highly favoured by the Dutch growers.