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Growing Microgreens On Rockwool – Guide

Growing microgreens hydroponically is a very fun process. Hydroponics is a method of growing plants without soil, on an inert substrate, using a regularly supplied balanced nutrient solution.

There are many substrates for hydroponics, but based on experience in greenhouse vegetable growing, we will choose special rock wool for growing microgreens as the most sterile, inert, and mechanically resistant substrate.

Growing Microgreens on Rockwool

Cultivation of plants on rock wool began in Denmark in the 70s of the XX century. Now this substrate is produced in many countries.

This substrate is easy to use due to its low bulk density – 80 kg / m3. Its high porosity (95-97%) allows it to have enough air in the root zone, even with significant moisture content (80%).

Forms Of Rockwool

Rockwool is produced in the form of standard products: corks, cubes, and mats.

  • Cylindrical plugs with dimensions of 23×28 mm are installed in a foam polystyrene cassette for 240 cells, but it can be cut to size. The plugs are intended for sowing small-seeded crops.
  • Cubes, as a rule, are made with two types of holes: for direct seeding (1.5×1 cm) and for picking corks.
  • Mats with dimensions of 100x20x7.5 cm are mainly used in vegetable growing.

Rockwool is an inert substrate, i.e., it does not bind from the solution and does not release any substances into it. Therefore, one must be very careful about plant nutrition.

The main requirements are no watering with clean water and top dressing with dry fertilizers. The nutrient solution supplied to plants must contain all the necessary macro- and microelements. Solution recipe (unit of measure – mg / l):

  • EC (concentration) 2.0 mS / cm, pH 5.5.
  • A balanced solution can be prepared by mixing 2-3 types of complex fertilizers.

Some might argue that different plants need a different ratio of nutrients. Right. This is used on an industrial scale, but for several dozen plants, it is inconvenient to calculate and dilute a dozen different solutions.

Still, if desired, this can also be done. However, nutritional recommendations for different plants should be clear, not “more nitrogen, less potassium”, but specific values.

Growth Solution

All flowers and vegetables grown in the same solution; there is no deficiency or excess of elements. This can happen if there is an unfavorable pH in the solution, even if it contains all the elements.

Therefore, if you decide to grow a perennial on mineral wool and do not have a pH meter and conductometer, it makes sense to use a ready-made solution (our advice to buy fertilizers from the GHE series).

Microgreens can be grown with a pick – this allows you to reduce the cost of heating and lighting. Besides, a small sprout does not need a substrate volume of 0.5 liters (cube).

Before sowing, the plugs must be fed with a solution; for this, it is advisable to use a container of appropriate dimensions, into which the entire cassette can be immersed. The corks are well saturated, a couple of minutes underwater is enough.

The use of a container will lead to slightly higher consumption of the solution than with regular watering. Still, later this will facilitate the maintenance of the water regime of the plants.


Unfortunately, plugs made of domestic cotton wool do not yet have a hole for the seed, so it must be made manually. It should be conical, no deeper than 2-3 mm.

I don’t prepare seeds for sowing; I sow immediately. Having placed the seed in the recess, sprinkle it with vermiculite or perlite (you can use organic materials – peat, sawdust – but where is the guarantee of their sterility?

However, sprinkle only relatively large seeds. Too small seeds are not sprinkled after sowing; on bags of such seeds, they usually write that the crops after moistening must be covered with film or glass. The same is done with the sprinkled seeds; the film is removed when 50% of the seedlings appear.

Temperature and humidity conditions are individual for each plant species. Well, if they can be observed, the seedlings will be more friendly. I have all the crops in one place.

Approximate temperature conditions – 18-19 ° at night and 20-21 ° during the day; in winter, plants are illuminated with Reflax lamps for 20 hours.

To control the moisture content of the cork, you can use the following technique: carefully remove the cork from the cassette and gently squeeze it with your fingers: if the solution remains on your hands, then the humidity is sufficient, watering is not required.

Usually, the extreme plants on the cassette dry out first, and you can navigate by them: if such seedlings have lost their turgor, it means that it is time for watering for the rest of the seedlings in the cassette.

For watering, it is enough to lower the cassette by 2/3 of its height into the solution, wait 1 minute.


Seedlings dive when they begin to compete for light (leaves of neighboring plants close up). If there is an additional cassette, you can place the plugs wider. Further cultivation of plants can be continued in normal soil. The transition from rock wool to the soil is almost 100% successful for the roots.

The cubes must also be saturated with a solution before picking seedlings. A rock wool cube will soak faster if it is completely immersed in the solution.

The corks in the cassette are gently pushed from below and transferred to the cube. The resulting voids between the walls of the cube and the cork are covered with loose material, carefully watered with a solution, or moistened with it from a spray bottle.

The cubes are placed on a smooth and even surface, or on a film (to improve illumination – on a white one).

If the cube is used for direct sowing, then germination in it is carried out in the same way as in corks. Over time, the top layer of mineral wool “turns green”. The development of algae on a damp, illuminated surface is normal; it serves as an indicator that there are no substances toxic to plants in the substrate.

The correct watering regime is the most important thing in this technique. It is very important not to over moisten the substrate – if there is a lack of oxygen, the roots die.

Developing Seedlings

Typical recommendations: the moisture content of the cube should not fall below 50%; the weighing method is used for control.

Weigh the cube immediately after picking. Wait until it has lost half of its weight, pour 50-70 g of the solution and then maintain the weight within these limits. But these are only general recommendations.

If the plant withers, you dry out the cube. If, after watering, a solution accumulates on the film, water it. It is advisable to maintain a water regime appropriate for the type of plant. For example, a gerbera needs drying between waterings, so you shouldn’t keep even constant humidity in the cube (but be sure to water it in time!).

An important point is the temperature of the root environment; it should not fall below 16 °. Otherwise, it will lead to a delay in root growth, to a decrease in their absorption capacity (it can cause chlorosis or even wilting), to the development of pathogens.

Cubes can be planted in the ground (if growing annuals). You only need to remove the film from them; the whole cube is buried in the substrate.

When transplanted into the ground, rock wool quickly loses moisture (because there is less moisture in the soil). Therefore, while the plants have not taken root, they need to be watered often – you can use plain water.