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Stone wool arrives at the greenhouse disease-free. Whether soil diseases are able to penetrate is dependent on the level of hygiene within the company. Naturally, the plant material must also be absolutely disease-free. The careful setting up of the system, the use of ground sheets and properly packaged slabs will limit the risks still further. Should any problems nevertheless arise, they are then relatively simple to resolve. That is the advantage of the small root volume.
Stone wool is a mineral wool made of volcanic rock. Stone wool consists of 5% solid material in the form of stone fibres. The remaining 95% is made up of pores.
The basic materials for Grodan stone wool are Basalt and Limestone. These are melted to form lava in an oven with a temperature of 1,500°C. The lava is then poured over a number of fast-rotating discs. Thanks to the centrifugal force, the drops fly off the discs and lengthen to form fibres. The process can be compared with candy floss being made at a fair. The fibres are then compressed to form a sturdy mass, from which the slabs and blocks are then cut.
Stone wool slabs not only need to absorb sufficient moisture but also need to distribute it over the entire volume of the slab. Grodan stone wool has been specially developed to satisfy these requirements. If the moisture were to sink to the bottom straight away, there would be dry or salty spots in the slab. The roots would not thrive in such an environment, so the “rootable” volume would be reduced. A good “capillary action capacity” (water distribution) ensures that the entire slab volume can be controlled and thus also fully rooted.
With a controllable substrate, the crop has access to whatever it needs at that moment. The plant will therefore respond optimally and thus also be more productive. With Grodan stone wool substrate, the slab volume can be controlled right down to every little corner of the slab volume. Comparable results may be possible with other substrates, but would require around 10 to 15% more water and nutrients.
In the first instance, the water buffer must be able to cushion a temporary disturbance in the nutrient unit. A substrate with a lower “capillary action capacity” is more susceptible to drying out. In addition, the shocks in EC, pH and temperature in a substrate with good capillary action and with a water buffer are less extreme. Savings in terms of water and nutrients thanks to the controllability of stone wool substrate are of course also important if recirculation is to be applied. With a water buffer, there are far fewer cubic meters of water to be disinfected, so the disinfection costs per square metre are lower.
Compared with soil, substrate slabs have a smaller volume. However, it is important that that volume can be used fully by the roots. After all, if the weather suddenly changes, a plant needs all its roots in order to be able to cope with the extra transpiration. If the substrate is not fully accessible for root development, there will be risks in the event of changes in the weather leading to a significant difference in evaporation.
No, since the moisture content of a slab is determined by the evaporation and the watering. Not using trickle irrigation and allowing extreme transpiration in the plant (hot pipes) will automatically lead to the slab drying out. In other words: the moisture content in the slab is controllable. In principle, we strive for a lower moisture content in the winter. We can achieve this by allowing the crop to transpire sufficiently (minimum pipe temperature, fast ventilation) and through holding long pauses in between the watering sessions.
The water content in the stone wool slab can be assessed with the aid of the Grodan water content meter (WCM). This indicates the current water content of the slabs precisely so that the water content variations can be closely controlled. The WCM also measures the EC and the temperature of the stone wool slab.
The clean and controllable stone wool-based growing solutions of Grodan promote the production of high-quality vegetables and plants. Further, cultivation on this growing medium is in line with the drive of Grodan to achieve a more sustainable world.At the end of the 1960s, environmental objections against the increasingly intensive land use in the horticultural sector mounted. One result of these objections was that the commonly used soil disinfectant, Methyl Bromide, was prohibited by law. Likewise, steaming the soil, which was very expensive and labour-intensive, fell out of favour. In the search for an alternative, the parent company of Grodan, the Danish stone wool manufacturer Rockwool, in cooperation with a number of universities, investigated the possibilities of cultivation on stone wool substrate, eradicating the need for soil altogether. This was the solution the World had been waiting for: crops proved to grow extremely well on stone wool. The result was immediate increased production with less water and nutrients.Shortly thereafter, Rockwool/Grodan in Denmark opened the first line for the production of stone wool substrate. Ten years later, a similar line was launched in Roermond. This production location grew into the biggest stone wool factory in the world. Roermond is where stone wool substrate was developed into what it has become today: a growing medium that enables growers to cultivate safe and healthy products sustainably, controllably and efficiently. Stone wool Stone wool is a natural product. It is made from Basalt, solidifiedlava spewed from the innermost depths of the earth. In the mid-nineteenth century, American geologists on Hawaii discovered a “woolly” material consisting of stone threads, which the local inhabitants were using to insulate their huts. This was a volcanic material, the product of red-hot steam being forced through liquid lava under high-pressure. To produce stone wool commercially, Grodan/Rockwool duplicated this natural process as closely as possible. Today, extracted basalt is re-liquefied in furnaces at a temperature of 1,500 °C. The liquid Basalt is then spun into threads in spinning chambers, and then congealed in a hardening kiln using hot air (230 °C) and compressed into wool packets, which are then cut into slabs, blocks or plugs and packaged in film. With factory processing, one cubic metre of basalt can produce approximately fifty cubic metres of stone wool. The advantages The use of stone wool substrate offers many advantages. Thanks to the controlled manufacturing process, this growth medium is of a consistently high quality. The sterile production under extreme temperature ensures that the product is clean and sterile. Its unique hydrophilic fibre also makes the cultivation on stone wool substrate very easy to control. The grower can administer the amount of water and nutrients the crops need in a very directed and controlled manner, to achieve optimal growing results. Waste becomes a thing of the past. Efficient use of water and nutrients keeps yield per square metre high, and energy consumption per unit of product low. Additionally, the product is lightweight, making it easy to use. And last but not least, stone wool can be easily re-used. To sum up, it is a sustainable and environmentally-friendly product.