Tray of 24 x 36mm grodan rockwool propagation cubes for growing seeds or taking cuttings. Rockwool is a very popular growing medium for propagation as it has a good air to water ratio even when fully wet and large numbers of cuttings or seeds can be grown quite easily. 36mm Rockwool Cubes – Tray of 24 Usage: All rockwool cubes, blocks, slabs etc always come with a slighly alkali pH so prior to use if you want to achieve the best results you must pre-soak your rockwool. Get a small bucket or container and fill it with water, adjust the pH of the water using pH down and a Ph test kit or digital meter so the pH is 5.2 to 5.5, then drop all the rockwool cubes you are going to use in and leave for 12 to 24 hrs. Your rockwool has a pH of 6.5 to 6.8 so by pre-soaking in the lower pH solution it will stabilize around 5.8 to 6.2 which is the desired level for hydroponic growing. When re-wetting your cubes during the cutting process always make sure your solution has a pH in the range 5.8 to 6.2
