Worm Tea For Hydroponics

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“Can you use worm tea for hydroponics?” ~ Jacinta Lederhose

Hi Jacinta,

That’s a very interesting question and something I’ve also wondered about, but have yet to test out myself. Your question inspired me to do some more research to see what I could dig up.

Firstly, while I’m confident that most people know what hydroponics is, for the benefit of those who don’t, here is how Wikipedia defines it:

“Hydroponics is a method of growing plants using mineral nutrient solutions instead of soil. Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite, gravel or Rockwool”.

In most cases the nutrient solutions contain a specifically-formulated (for the particular plants being grown) inorganic fertilizer, and considerable effort is made to keep the process as sterile as possible to reduce the chances of diseases developing.

Both of these characteristics (inorganic & sterile) essentially run counter to the rationale for using worm castings / worm tea – since they are organic fertilizers (although not necessarily “certified organic”), and one of the benefits is the rich microbial community present.

That being said, there IS a growing (no pun intended) interest in the concept of ‘organic hydroponics’, and various organic nutrient solutions – including those usings worm castings – are indeed available for purchase.

Some people report being able to use worm tea successfully in a hydro system, although the addition of other organic fertilizers (such as bat guano and kelp) may be necessary since worm castings have relatively low nutrient levels on their own. Terracycle – a popular brand of worm tea – for example lists NPK ratios in the range of 1:1:1 (this varies slightly amongst their different products). This is comparable to values commonly cited for solid worm castings as well (have seen somewhat higher values though).

As research has shown – and these low values would seem to indicate – there is something beyond basic nutrient levels that is responsible for the growth promoting ability of castings and worm tea.

One of the potential issues of adding a rich microbial solution to a hydroponic system is that sludge can accumulate and plug up equipment, not to mention using up considerable amounts of oxygen (which is very important for healthy root growth, along with the growth of many beneficial microbes). Some suggest sterilizing the solution with hydrogen peroxide prior to use, but to me this seems to potentially defeat the purpose of using worm tea at all.

I came across one particular technique for organic hydroponics that sounds as though it would lend itself very well to the use of worm tea and other rich organic nutrient solutions (or even solid worm castings) – without requiring sterilization.

This technique involves the use of a ‘flood and drain’ hydroponic set up (lower reservoir periodically pumps liquid into upper plant growth tray – excess liquid then drains back down to reservoir).

Unlike a typical flood and drain hydro set up however, the reservoir simply contains plain water, not nutrient solution.

Each plant pot sitting in the upper tray will essentially be split into two zones. The upper zone will contain a soil like medium and this is where the organic fertilizer will be added, while the lower zone will contain a course lava rocks (or something similar) and will simply help wick moisture up into the growth zone whenever water is pumped up from the reservoir.

Be sure to check it out: http://hempbc.com/articles/1534.html (simply avert your eyes from the hemp plants being grown! Rest assured this method applies to ‘normal’ plants as well. haha).

Another related system where worm tea (and worms themselves) could potentially work very well is an ‘aquaponics’ set-up (which uses aquaculture effluent to fertilize plant grow beds), but I’ll have to leave that discussion for another day. 🙂

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