I have been collecting info on rockwool cubes a long time. Let me share what I have learned.
Rockwool comes with a warning label, like abestos, to not handle it dry, because it has carcegens in it, or can cause cancer IF you breathe in enough of it's dust.
SO, you do need to really soak it A LONG TIME to handle it, but it will only take a minute to soak it and make it safe from DUST flying around. It will take a few hours or more to soak it to adjust it's pH.
The instructions on rockwool sent with the SH BB kit says to leave the plastic on. That is because they fear for our safety and do not wnat us exposed to carcegens. I remove the plastic but I do soak it. I butt the tube into the side of it when I prepare my cups.
Rockwool is probably the most popular growing medium on earth. Rockwool was originally used as insulation and was called "Mineral Insulation". It was developed for gardening in Hydroponics in Denmark and is used extensively around the world for "Drip-Style" hydroponic systems.
Rockwool is made by melting a combination of rock and sand and then spinning the mixture to make fibers which are formed into different shapes and sizes. The process is very similar to making cotton candy. The shapes vary from 1"x1"x1" starter cubes up to 3"x12"x36" slabs, with many sizes in between, which makes rockwool one of the most versatile growing mediums.
The advantages to rockwool are many, however there are several disadvantages to this type of growing medium as well. The pros and cons are listed below.
Advantages of Rockwool
RETAINS WATER - Rockwool holds an incredible amount of water which gives you a "buffer" against power outages and pump (or timer) failure. You want your rock wool saturated and it saturates well, plus it holds air too.
HOLDS AIR - Rockwool holds at least 18 % air at all times (unless it is sitting directly in water), which supplies the root zone with plenty of oxygen. This means that it is practically impossible to over-water rockwool.
COMES IN A VARIETY OF SIZES AND SHAPES - From 1" cubes designed for use in propagation, to 3"x12"x36" slabs capable of holding the root systems of huge plants, rockwool comes in dozens of shapes and sizes making it a versatile growing medium. Rockwool also comes "Loose" so you can fill pots or containers of any size.
CLEAN AND CONVENIENT - Rockwool holds together very well so it can't spill. Rockwool also comes wrapped in plastic, which makes it easy to handle and keeps evaporation to a minimum.
Disadvantages to Rockwool
NOT ENVIRONMENTALLY FRIENDLY - Rockwool is hard to dispose of, if buried it will last indefinitely.
DUST AND FIBERS ARE A HEALTH RISK - The fibers and dust from the rockwool are bad for your lungs. Wear a dust mask when handling it dry, to prevent problems. Soaked and Saturated, it is safe.
pH PROBLEMS - Rockwool has a high pH which means you have to adjust your nutrient solution low so that the root zone is neutral. Pre-Soaking it in 4.5 to 5.0 water is advised.
Getting Started with Rockwool
Before you use rockwool you must first soak it in water adjusted to a pH of 4.5 to 5.0. To soak rockwool cubes use a bucket or other water tight container, just put the cubes in the water and let them float around. To soak the rockwool slabs cut a hole in the bag around the slab and pour in pH adjusted water until the slab is totally saturated, let soak for up to 8 hours to be safe. Then cut drainage slits in the bottom.
Using Cubes
Rockwool cubes come in many different sizes. There are two sizes of "starter cubes" that are designed for propagation. The 1" x 1" x 1 1/2" and the 2" x 2" x 1 1/2" cubes are not wrapped in plastic and are normally used for starting seeds. The 1 1/2" x 1 1/2" x 1 1/2" cubes are wrapped on four sides with plastic to slow evaporation and are used primarily for taking cuttings.
The 3" and 4" cubes can be used as the primary growing medium or in conjunction with other growing mediums. For small plants a large cube may be all the growing medium that you need. For larger plants these cubes are used as an intermediate medium that gets transplanted into a different type of growing medium as the plants grow.
The larger cubes come with or without a hole that is designed to fit the 1" cube. With the hole you can easily transplant the 1" starter cube into the larger cube simply by inserting it into the hole.
