Houseplants in hydroponics

The word ‘hydroponics’ simply translates to ‘water cultivation.’ Plants don't necessarily need soil to grow well and stay healthy. They mainly rely on water, nutrients, and air. The soil in garden beds or pots primarily provides stability for the plants.

In expanded clay, houseplants can stand just as securely. Therefore, you can plant all kinds of plants in hydroponics. This even applies to water-sensitive species like cacti or orchids.

A special and very trendy form of hydroponics is hydroponic cultivation, where plants are grown only in water. This method requires even less effort and is a clean process but results in slower plant growth. Hydroponics doesn't work for all plants, but the following are well-suited: anthurium, alocasia, bromeliad, clusia, Ficus benjamina, aglaonema, dragon tree, orchids, and philodendron.

Make sure the plant is securely positioned in the container. Bulb-shaped vessels or tall glasses with a stable base work well for this. The visual contrast becomes especially interesting when you place the glass on or inside a plant stand or flowerpot made from tree trunks.

If you want to try hydroponics, you can purchase suitable houseplants from specialist stores that are already potted in expanded clay. Alternatively, you can repot your existing houseplants in the spring.

Take the plant out of its pot and gently wash the soil off the roots. Try to remove as much soil as possible from the roots. If you notice any dead or rotten roots, trim them off with a clean pair of scissors. The EasyPrune from Bosch works well for this, as it cuts cleanly without crushing the delicate roots. Next, place the plant with its bare roots into a hydroponic pot. These pots have a special inner pot. First, insert the plant, followed by the water level indicator. Then, fill the pot with the expanded clay pebbles.

Once the pot is full, gently tap it on the floor or a table. This helps the expanded clay pebbles move around and fill any remaining gaps. This ensures good contact between the roots and the material, giving the plant stability. Place the inner pot into a waterproof outer pot.

It will take a few weeks for the plants to establish themselves in the expanded clay. You can monitor the water supply using the water level indicator. Don’t overwater. Add just enough water so that the level indicator is at or near the minimum mark. Only water the plants again when the indicator falls below this mark. The minimum line shows that there’s still about 1 cm of water left in the pot.

Only in exceptional cases should you water enough for the indicator to reach the maximum level. For example, this might be useful before going on holiday when you want to water your houseplants in advance. If the plants receive too much water over a prolonged period, the roots can start to rot because they won’t get enough oxygen in the pot.

If you have small plants, you can also cultivate them in hydroponics using test tubes. Two decorative DIY ideas made from wood are wall-mounted holders (also perfect for cuttings) or standing holders, which also look lovely on a table.

Every two to four weeks, you should give your hydroponically grown plants a special hydroponic fertiliser. It should be low in concentration, avoid using regular houseplant fertiliser, as it contains too high a nutrient concentration. 

Only repot your houseplants in hydroponics when they have outgrown their current container. This often takes several years, as hydroponic plants do not grow as quickly as those in soil. Instead of repotting, remove about 2 to 4 cm of expanded clay pebbles from the pot each year. They often turn white due to the nutrient salts that accumulate in the pebbles. Take them out and rinse them with clear water. You can then reuse the expanded clay for your plants.

Clay pebbles store water very effectively. The material is comparable to a sponge; it absorbs water and gradually releases it to the roots.

If you want to transfer your plants currently growing in soil to a pot with clay pebbles, do not rinse the roots. Instead, transplant the plants with their root ball intact. Fill the remaining space in the pot with the clay pebbles.

Use a waterproof outer pot that is about one-third larger than the old flowerpot. Add enough clay pebbles to the bottom so that it fills approximately one-third of the total height of the pot. Place the plant with its root ball on top of this layer. Then, fill the edges with clay pebbles as described above. Make sure to add some clay pebbles on top of the root ball as well, covering it by about 2 cm.

Instead of inserting the water level indicator at the edge of the pot, place it straight or slightly angled into the plant’s root ball. The indicator will measure the moisture of the root ball rather than the water level. If the indicator is blue, you don’t need to water yet. If it turns red, it’s time to water your houseplants again.

Always add enough water to fill about a quarter of the pot. It’s helpful to note the pot volume before planting. After watering, it may take some time for the moisture indicator to turn blue again. Overall, a plant in clay pebbles requires less frequent watering, as the pebbles retain water very well.

With the help of water level indicators, you can easily monitor the water supply at the bottom of your hydroponic plant's pot, this helps to prevent waterlogging.

Houseplants in closed pots require more care. The amount of watering must be measured very precisely, as roots can quickly die from lack of oxygen if there is waterlogging.

With special planting systems, maintenance becomes easier. Within these systems, the root ball does not sit on the bottom of the pot but is elevated above it on a separate layer. This creates a space beneath where water can be stored without the roots suffering from waterlogging. This water reservoir keeps the soil moist.

Since there is always a supply of water in the pot, you need to water much less frequently. Water is added to the plant container through the watering shaft located at the edge of the pot. A drainage layer made of gravel, lava rock, or clay pebbles above the separating layer ensures that the roots do not extend into the water. This layer should make up about one-fifth of the total height of the pot.

An exciting plant project in water culture is growing an avocado: from seed to plant.

If you want to know more about when certain gardening tasks need to be done, you can find that information in our garden calendar, which provides the right timing for all important activities.