Passive hydroponics is one of many methods to grow plants without soil. Growing medium is inert and wicking. It delivers water with fertilizer to the roots by means of capillary action. Substrate contains many small air pockets and can thus deliver oxygen to the roots. The method has been applied to orchids.
Orchids can be planted in any non glass container. The 3-4 drainage holes are placed not at the bottom but 3-5 cm up, at the sides of the pot. The idea is to provide a water reservoir at the bottom of the container from which the medium wicks moisture to the roots.
LECA (Lightweight Expanded Clay Aggregate) - expanded / fired clay pellets or clay pebbles , perlite, vermiculite, diatomaceous earth, gravel, charcoal, rockwool, coconut husk chips and their combinations.
Substrate is flushed with tepid water solution when reservoir is nearly empty. Translucent pot may help to see when it is.
Orchids are fertilized with 1/2 to 1/4 of recommended strength of balanced inorganic fertilizer with every
watering. Container is flushed with plain water every month to prevent harmful salt build up.
Conversion from conventional culture to passive hydroponics
- New medium is washed and then soaked overnight. The plant is then removed from the old pot and substrate is removed from the roots. Rotten or overlong roots are cut / trimmed away. All the roots are thorougly washed with lukewarm water.
- Some new medium is placed at the bottom of the new container. The plant is accommodated and more new medium is put around. The pot is gently shaken, more medium is put in, more shaking and so on. Container is flushed with tepid water. The orchid is placed in the shade without fertilizing the following month.
Which orchids can be grown?
Most popular orchids will more or less thrive in hydroponic culture: Paphiopedilum, Phragmipedium, Masdevallia, Phalaenopsis, Cattleya, Cymbidium, Oncidium, Dendrobiums, Epidendrums, Miltoniopsis, Pleurothallid and Zygopetalum.
- Exceptions would be very big or "thirsty" plants or those whose roots must sometimes completely dry and even those that require dry rest like Dendrobium nobile.
Advantages of Passive Hydroponics
Its simplicity and effectiveness. No guessing about watering and fertilizing, no media decomposition, practically no root rot, healthy plants, fine blooming, no moving parts, low cost, reusable media.
- In hot and dry environments passive hydroponics is beneficial since the roots stay in a high humidity chamber with some air flow.
- The main disadvantage is sometimes need of more frequent watering, especially when plants begin to fill their pots, are big or otherwise demand lots of water. Obviously, a bigger pot / reservoir may help.
- If the translucent container receive enough light then algae will grow on the outer layer of the potting media. This is mainly an aesthetic concern and not a big problem indoors.
- If the medium consists of expanded clay pebbles and the plant is newly established then tipping it over may cause the spilling of the medium and plant.
- Build up of salts from fertilizer and water are not easily removed from clay substrate. Also, excess of chemicals used for pest or disease control is retained.