Hydroponic Growing Media at a Glance

1. Because it acts as a filler medium, the material should be permanently dimensionally stable. In other words, it should swell or shrink as little as possible under changes in moisture and temperature, and above all it should not compact over time.
2. The substrate has to be highly permeable to air and water and should support capillary action. The roots absolutely need a good air supply, so that no rot develops in what is otherwise a very moist environment.
3. The material itself must not be prone to rot. On top of that, keep in mind that it must not react with the nutrient solution either, but stay neutral and not break down over time.
4. The nutrient solution must not react with any components of the material. Otherwise, nutrients could become ineffective or even harmful to the plant.
5. The grain size should be chosen so that it allows healthy root growth and meets the plant's natural needs.

Pros and cons of net pots in hydroponics

Net pots come into play whenever the root system is allowed, or even meant, to spread outward. This matters, for example, with the currently very popular Deep Water Culture (DWC) method, where the extra oxygen is absolutely essential for the plant's boosted growth. In systems like these, growers also use clay pebbles or rockwool, but never soil, coco or similarly loose substrate, because hydroponic setups are always connected to a pump system that does not take kindly to clogging from loose media.

Pros and cons of perlite in hydroponics

Perlite starts out as a volcanic glass, obsidian, which makes it a rock. It is a natural glass formed from lava that cooled very quickly on contact with water or steam under intense pressure. This so-called raw perlite is first crushed, sieved and pre-dried before being briefly heated and dried at around 1000 °C. During this process the raw perlite expands to fifteen to twenty times its original volume and takes on its characteristic white colour.
This substrate is sterile too, and therefore free of weed seeds and pests of any kind. It can only store small amounts of water and nutrients, but in return it has excellent water and air conductivity.
In Europe this material is mainly quarried on the island of Milos in Greece. Since this raw material is continually replenished through natural volcanic activity, it is considered a renewable resource that you can use with a clear conscience.
You may also come across perlite under the names Perligran and Perlite.

Tips for using perlite

• For hydroponic growing, use grain sizes up to 3 mm.
• Water the substrate thoroughly before using it for the first time.
• Perlite can be used on its own as a propagation medium, but it also mixes very well with vermiculite, for example. That combination makes an excellent substrate, since the two components complement each other nicely in terms of water storage capacity and air permeability.
• When moistening the substrate, avoid breathing in the dust that rises up.

Pros and cons of rockwool in hydroponics

Rockwool blocks are made from molten, spun rock. Together the fibres form a stable mat. The following rock types are used to make it: dolomite, basalt, diabase, anorthosite and spar.
When dry, this substrate is exceptionally light, because it consists of a very porous material with 95-97 % pore content and just 3-5 % dry matter. That is also why rockwool has an extremely high water absorption capacity of 90 %.
Thanks to the extremely high temperatures generated during production and the stone raw material, the substrate is completely sterile. So it certainly contains neither weed seeds nor any form of pest. Rockwool is of course inorganic. That fact, combined with its sterility, good water and air permeability and high water absorption, makes rockwool a very suitable substrate for hydroponic growing. In Europe, rockwool has become established under the name Grodan. You can buy it both as rockwool slabs and as pre-made cubes in every size imaginable.

Tips for using rockwool:

• Rockwool works for every hydroponic system.
• Before use, water the material thoroughly once so it can soak through and become well saturated with water or nutrient solution.
• The pH of rockwool is relatively high, at 7.5 to 8.5. But since rockwool has almost no buffering effect, even small amounts of a physiologically acidic liquid fertiliser are enough to bring the pH down to the level you want.
• Use nutrient solution with every watering. This approach is tried and tested and gives the best results. A readily water-soluble complete fertiliser with trace elements is entirely sufficient.
• If you happen to pre-soak too many rockwool blocks, no problem at all: just let the blocks dry out again and reuse them later.

Pros and cons of vermiculite in hydroponics

Vermiculite (from the Latin vermiculus, "little worm") is a clay mineral, also sold as "expanded mica". The name vermiculite comes from the mineral's property of curling up into worm-like shapes when heated to 200-300 °C. The mineral belongs to the silicate class and occurs only rarely in nature.
As a clay mineral it has the typical properties of one, such as very good water storage and a high ion-exchange capacity, which in simple terms means it can store plenty of nutrients. This significantly improves soil fertility, which is why vermiculite is increasingly added to potting soils as a peat substitute, since peat performs similar functions.
Another positive property of vermiculite is that it reflects light while having low thermal conductivity. These properties are put to use when vermiculite is used as a top dressing in plant cultivation. On the one hand the young plants are very well supplied with water and nutrients, and on the other they are protected from overheating and excessive radiation.
Natural deposits of vermiculite are found mainly in South Africa and Australia.

Tips for using vermiculite

• Water the substrate very thoroughly before first use, to fill its water reservoirs completely.
• Thanks to its good water storage capacity, low thermal conductivity and light reflection, vermiculite is particularly well suited as an outdoor propagation medium in regions with a very hot climate.
• Mix vermiculite with perlite in a 1:1 ratio and you get an ideal propagation substrate for hydroponics, because both media have a very similar density and complement each other perfectly in terms of water storage and aeration.