ROCKWOOL: As Potting Medium
It is inert, a spun rock, like fiberglass, it comes in three grades -- fine, medium, coarse -- and in both absorbent and non-absorbent types, including Grodan horticultural grade, available in 3 or 4-inch growing blocks which are absorbent; the advantages claimed for it include -- sterility, inertness, ease of repotting, its maintenance of a 15% air space, it provi des for fertilizer control; its disadvantages are its high cost originally and the care required to achieve correct fertilizer levels; it has to be kept wet; for odontoglossums it requires a 20-20-20 fertilizer. RMHIt is used for growing cymbidiums. A85-841It is volcanic rock melted down into cot tony fibers, it is inert, sterile and does not decompose; po11 ing-on is possible without di sturbing the root ball; the pH is perfect when watering with commercial 20-30-20 fertilizer; advt. A88-332This is the name given to several commercial insulating materials on which orchids can be grown by adjusting the watering and fertil...