Advantages
Rockwool has many advantages for hydroponic production: the manufacture of the rockwool fibers from molten rock and plastic wrapping of growing slabs ensures the product is sterile, and free from weed seeds, pests and pathogens. High quality rockwool brands, being a manufactured product are also consistent in quality and don’t decompose or break down over time in the way that many other natural growing substrates do. Rockwool maintains it physical properties over time and with successive crops. Rockwool is light weight and thus easy to handle and shift into place, once fully irrigated however it becomes heavy and provides stability to the crop.
Rockwool comes in a convenient range of sizes from small 2-3 cm propagation plugs joined in sheets for direct sowing crops such as lettuce and other seedlings, to large cubes of over 10cm for more advanced transplants. Rockwool plugs are often used for cuttings where they maintain the ideal levels of aeration and moisture for rapid root development. Rockwool can be inoculated with beneficial microbes such as Trichoderma in much the same way other substrates like coco are, however more frequent applications of microbial products are recommended with rockwool substrates. Most rockwool products and reliable brands don’t have any major influence on the EC, pH or composition of the nutrient solution applied. since rockwool provides no naturally occurring nutrients a well balanced nutrient product applied will give optimal growth.
Rockwool is manufactured to give a close to ideal level of moisture and aeration in the root zone, this helps prevent over watering and root suffocation from a lack of oxygenation.
Rockwool can be used for successive crops as its structure does not tend to break down rapidly with use or over time. some commercial tomato growers re use good quality rockwool for as many as 6 successive crops with use of steam sterilization to control root pathogens between plantings.
Rockwool products and growing slabs come ready to use, the substrate only needs to be thoroughly wetted before planting. Rockwool can be monitored with a water content meter which gives accurate measurement of the water content, EC and temperature in the plant’s root zone environment. These assist with fine tuning the application of nutrient solution to just the right level for each stage of growth.
Microbial characteristics of rockwool
Rockwool, being a ‘sterile’ product (only directly after production) does not contain any naturally occurring beneficial microbial populations when first planted out, however research has shown that microbial life does develop in rockwool substrates in the same way as other more `organic’ mediums such as peat and coco. This build up of beneficial microbial populations however is generally slower in rockwool as there are initially limited carbon sources for the microbes to feed on. as root systems develop and produce organic exudate, microbial life inside rockwool gradually build, however rockwool can be inoculated with microbial products to assist this process and help develop a healthy root zone. The high level of oxygenation in a well managed rockwool system also help with the establishment and multiplication of beneficial microbe populations.
Re-usage characteristics of rockwool
Rockwool, being essentially rock does not decompose, fracture or break down over time, hence growers can use it for many successive crops. However it is recommended that rockwool is steamed or at least treated with boiling water before replanting to help prevent any carry over of root disease pathogens. a thorough leaching with clean water also helps remove any excess salts from the previous crop. some smaller growers use chemical disinfectants to treat rockwool before use, however care needs to be taken to completely rinse these from the material before replanting and steam or hot water is seen as a much safer option. Eventually used rockwool material has to be disposed off – often growers simply dump this, however it is possible to shred the material and re use it in other growing mixes, or incorporate it into outdoor soils and gardens as a soil conditioner.
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Article source: cannagardening.com/ characteristics_of_rockwool