Let me say right from the start that I have nothing against growing plants plants the good-old time-tested way – in simple pots filled with good quality soil. As a matter of fact, most plants that I grow outside, on my balcony, are grown in pots with soil, where possible fitted with sub-irrigation reservoirs. However, as far as indoors growing is concerned, growing in soil has proved to be quite a challenge for me, and the main factor that has eventually led me towards passive hydroponics. I try to grow at least part of my edible plants inside my city flat, where air-moisture is so high that even occasional watering leads to quick appearance of mold on the surface of the soil. At other times, I’ve had to leave abroad for periods long enough to completely dry the soil and kill all but the hardiest of my plants. These two extremes have repeated often enough to make me look for a better solution.
Sub-irrigated planters with soil
My first step was to replace old clay pots by sub-irrigated planters fitted with a water reservoir and wicks to passively draw water to the plant. Sub-irrigated containers can be made from recycled PET bottles
, but harmful sbustances from PET plastic may leach into the water and soil, I prefer using professional versions, such as those made by Lechuza
that are not only safer, but also work better, although they are a relatively expensive.
Overall, transition to this growing method helped, since it did increase the intervals between waterings, but when I filled the tanks to the maximum level before going away for a longer period of time, the soil often absorbed too much water from the reservoir, leading once again to mold growth or worse – root fly infestation. At other times, the wicks on the contrary didn’t provide enough water for the plants to flourish.
Could the answer to my problems lie in growing vegetables hydroponically, i.e. without dirt, using merely water and a soil-less medium? According to online sources
, growing vegetables hydroponically is twice as fast, uses 90% less water, and yields 4 times the amount of crops per allocated space, without having to use any pesticides or insecticides. As great as this sounds, I realized that even hydroponics has its drawbacks and pitfalls.
Water circulation / Water oxygenation systems
Most hydroponic systems require recirculating a nutrient enriched solution between plants and a storage tank, or alternatively oxygenating water in which the plant’s roots are immersed.
The need for moving water or air through the system leads to relative technical complexity and maintenance needs as any clogged tubes or pump malfunctions can destroy the plants. Since I sometimes have to leave my flat for several weeks, this could happen quite easily. Furthermore, many hydroponic systems require electricity to power the water or air pumps, that in turn emit more or less background noise (even the quietest ones can be annoying if you grow pants in the same space where you sleep).
These considerations made me turn more attention to non-circulation hydroponic methods.
Non-circulation off-grid hydroponic systems
The first passive hydroponic method that I put into practice was hydroculture
, in which a plant is suspended in a container filled with clay balls (such as Hydroton) that offers a good balance between porosity and water retention, while providing the plants with physical support. The lower part of the pot with the growing medium is immersed in water with nutrients, which naturally rises by means of capillary action, making part of the clay balls above water level damp enough for the plant to to absorb water and nutrients from them. Specialized water roots sometimes reach all the way down to the immersed part of the growing medium to draw water. These roots, unlike regular earth roots, do not rot even when in water. Further up, the medium is progressively less moist while the balls in the upper part stay dry unless watered from the top.
From experience, I know that hydroculture works well for some plants, however, the intensity of capillary action is not very strong, and may be insufficient for more water-demanding varieties, especially vegetables. These plants may stay alive, but do not really thrive. Furthemore, water with nutrients has to be refilled quite regularly depending on the size of the planter.
A more convenient method of non-circulating hydroponics, which I intend to review in substantial detail in future posts, has been thoroughly described and tested by professor Kratky of the University of Hawaii.
This unique and promising method (for simplicity referred to as the ‘Kratky method’) is suitable especially for growing salads, cucumbers and other water-thirsty vegetables that would merely languish in a hydroculture set-up.
It consists of suspending a seedling plant in a net-cup (or any small planter with holes filled with growing medium) in the lid of a container with enough water-nutrient solution to keep feeding the plant all the way to harvest. At the outset, the water level reaches up to the net-cup, thus providing moisture to the seedling. Later, as water level slowly drops, the plant’s roots continue to grow out of the net-cup, maintaining contact with water and absorbing water with necessary nutrients. The upper portion of the roots remains suspended in the moist space between the the lid of the container and the water level, allowing the roots to absorb oxygen. Although the water level drops significantly over time, the roots grow fast enough to keep up.
According to testimonies found online and the studies published by Professor Kratky himself
, the Kratky method makes it possible to grow healthy plants from seedling to maturity with no circulation of water, no aeration, no electricity, no noise, and no water added of water during the lifetime of the plant is necessary.
In a nutshell, this sounds like the holy grail of hydroponic methods for fans of low-tech farming. Therefore, many posts of this blog will be dedicated to this particular method.