What is semi-hydroponics?

Semi-hydroponics, or “semi-hydro,” is a method of growing plants in a mineral substrate without soil or peat.
It often consists of a mix of different rocks and minerals, such as expanded clay, zeolite, or various volcanic rocks.
This growing method is becoming increasingly popular because it contains no organic matter, so it does not decompose and can be reused multiple times.
The minerals and rocks used are mostly porous, meaning they contain many small pores and cavities that hold water or air. As a result, the roots receive much more oxygen, which reduces the risk of root rot and promotes faster root growth.

How do I transfer plants into semi-hydroponics?

When switching from soil to hydroponics, it is important to remove all soil from the roots, which is easiest to do by rinsing the roots under water. If soil remains on the roots, you risk root rot.

Choosing the right pot.
The most important thing is that the pot is clean and free of soil residues. We use transparent nursery pots because they make it easier to monitor root development. Self-watering pots with built-in reservoirs and moisture indicators are also very commonly used.

Rinse the substrate under running water to remove dust and fine particles.

Add the first layer of substrate to the pot, place the plant on top, and fill the pot with substrate until the roots are covered.

Water the plant and leave some water in the decorative pot or tray so the substrate can wick moisture up to the roots.

Place the plant in a bright spot and, if needed, use a transplant stress aid.

If the substrate stays without water for a day, it’s not a big problem, but make sure it doesn’t happen too often or for too long, as water evaporates quickly from this type of substrate and the roots can dry out and die. But don’t worry too much—refilling the water is usually needed about every 14 days, though this depends heavily on the light conditions.

Which plants are suitable for semi-hydroponics?

The best suited plants are orchids, Hoyas, and aroids such as Monsteras, Philodendrons, Syngoniums, Alocasias, Anthuriums, and also those that prefer a slightly more humid substrate, such as Spathiphyllums and Marantas.
Strelitzias, Scindapsus, Pothos, Aglaonemas, Tradescantias, Pileas, Fittonias, and similar plants also grow well in this substrate.

We do not recommend this method for cacti and succulents, Sansevierias, Zamioculcas, and other plants that require dry periods between waterings. Plants with thinner, more sensitive roots—such as Begonias or Calatheas—may struggle to adapt and can decline or drop leaves after switching substrates.

Plants with thicker roots, like Monsteras, benefit from a coarser substrate with larger particles such as expanded clay (LECA), since the larger air spaces suit them well. You can mix some into the substrate.
Some plants may experience shock when transitioning from soil to hydroponics, so ensure they get enough light and be patient while they adjust.

What about fertilizing?

During the plant’s active growing season, you can add fertilizer with every refill of water because the substrate itself contains no nutrients. However, you must follow a few important rules.

The fertilizer must be mineral, as mineral fertilizers do not leave residues, dissolve well, and remain stable in water. Organic fertilizers are not recommended here, as they may begin to rot in the constantly moist environment, which can lead to bacterial root infections. Organic residues can also clog the substrate or produce unpleasant smells.

If you do use organic fertilizers, it’s recommended to occasionally “flush the substrate” by pouring clean water through the pot to wash out salts and organic buildup. The Biobizz series of liquid organic fertilizers is suitable for semi-hydro systems and is available in our store.

If you fertilize with every refill, use a lower concentration than indicated on the packaging—about ¼ to ½ of the recommended dose.

Why choose semi-hydroponics?

As mentioned earlier, this substrate is very porous and provides roots with both water and oxygen. Because the plant “sits” in water or has a full reservoir in a self-watering pot, it dries out more slowly, which means less frequent watering—and you can go on vacation without worrying 🙂
This method is also cleaner because there is no soil that can spill and make a mess. The substrate does not compact over time, which makes repotting easier.

Since some water evaporates, semi-hydroponics can help increase humidity, making it a great choice for plants that prefer higher humidity, such as Alocasias, Marantas, and Anthuriums.
Pests like thrips and spider mites dislike high humidity, so this substrate can slightly reduce infestations.
There is also a lower chance of fungus gnats laying eggs because there is no organic matter.

Are there any downsides?

Because the substrate is made of rocks and minerals, it is heavier than regular soil mixes, especially in larger plants. It can become quite heavy when the reservoir is full of water, making it less practical for shelves, hooks, or hanging planters.
Since the particles don’t stick together or compact, they provide less stabilization for the plant, and long, heavy trailing stems may occasionally get pulled out.

Many plants also dislike excessive handling of their roots during repotting, but removing all soil is essential for transitioning to semi-hydroponics. If soil remains on the roots, it can cause rot. Be patient and gentle when cleaning the roots. Rinse them thoroughly with room-temperature water.

Before use, it’s recommended to rinse the substrate, because friction between the particles creates dust that can clog pores and reduce water and air retention.
Plants with more sensitive roots may experience a strong shock when switching from soil to semi-hydroponics, sometimes losing one or two leaves as they adjust. We recommend monitoring the plant closely during the first few weeks.

Be careful not to add too much water and avoid letting the roots sit directly in water, as this can cause rot. Once the plant grows new roots in semi-hydro, these “water roots” become adapted to the environment and can grow directly in water.

In pots with larger drainage holes, smaller particles can fall through. In that case, you can place a fine mesh at the bottom of the pot.

What does the Only Plants semi-hydroponic mix contain?

When creating our semi-hydroponic mix, we chose four key components:

• 50% volcanic clay: porous, retains water and nutrients, provides aeration, stability, and capillary water movement.
• 25% zeolite: high cation-exchange capacity—absorbs nutrients and slowly releases them to the roots; improves substrate structure, prevents compaction, and helps stabilize pH.
• 20% quartz sand: adds weight and stability, preventing plants from tipping over; inert (does not decompose or affect pH).
• 5% perlite: lightweight and porous for better aeration and drainage; helps wick water upward by capillary action.