Worm castings, otherwise known as worm excrement, worm humus or worm poo, is actually extremely beneficial to your garden - and to your hydroponics system the same as any other excrement or manure. It contains trace minerals and nutrients vital to your plants as well as humic acids that have been linked with increased plant growth.
When a worm eats and digests organic plant matter it excretes castings containing nitrogen that has been 'fixed' to make it usuable to your plants. This is what a compost pile does; aerobic bacteria fixes nitrogen through the compost process.
Fixed nitrogen, a mineral salt, dissolves in water into ions and plants uptake this for nutrient. Does this mean that worm castings by themselves can be a soil substitute? No, it does not contain all needed nutrients, just some.
In fact the NPK rating of castings have been tested periodically and they average around 2-2-2 or 3-1-1 depending on the diet of the worms that created them. This makes castings a good soil adjunct but not a soil substitute.
Worm poo has gone through its own 'composting' process in the digestive system of the worms so is rich in bacteria - good bacteria known as aerobic bacteria. This is far more important to us who grow plants than the minerals found in castings.
Bacteria in the human intestines lives with us in a symbiotic relationship; while not something we want in our food and digestive tract, in our gut this bacteria helps suppress disease and bolster our immune system. The same occurs in a plant root system.
Aerobic vs Anaerobic Bacteria
Aerobic bacteria takes in oxygen and excretes carbon dioxide. These microbes live in a symbiotic relationship with a plant helping it maintain good health.
Anaerobic bacteria, on the other hand, does not need oxygen to survive. This grouping of 'bad' microbes can actually hurt your plant by stunting growth, damaging root systems and promoting disease.
A well drained garden will contain large colonies of aerobic bacteria and this includes hydroponics systems. This is why I never run hydrogen peroxide through my system to kill bacteria.
Keep the system clean and flush with water to promote growth of aerobic bacteria while discouraging anaerobic bacteria from taking hold.
This brings us to the second use of worm castings, making worm tea, which is, in my opinion, the best use of worm compost.
Worm tea will transfer huge amounts of aerobic, beneficial bacteria to the root system of your plants and can be used as a foliar spray as well. It will suppress insect attacks due to a high amount of chitinese which damages insect exoskeletons.
This makes worm tea an effective insect repellent and possibly a biofungicide of sorts. When worm tea microbes are sprayed onto plant leaves they may possibly be competing for food resource with other not so beneficial bacteria and maybe even fungus helping to eliminate them.
So the question remains...can worm tea and worm castings be used in a hydroponics system? They certainly could in a Mittleider hybrid system but would not do so well in a closed hydroponics system.
Particulate matter in the tea would tend to clog water pumps even if strained off. And since worm tea would contain some mineral salts which are the trace nutrients found in worm excrement it is possible a toxic amount of salts could build up quickly and damage your plants.
What is the level of mineral salts in worm compost? It all depends on the diet of the worm. A diet consisting of animal manure with mixed in urine would result in a high concentration of mineral salts. Chicken manure is notorious for this.
Using worm tea in a passive hydroponics system or container system would work well as long as the system and plants are flushed often and we do this anyway as part of routine hydroponics maintenance.
So how does one obtain a relatively free source of worm castings? Get a worm farm and use the worm compost for your plants or sell the worms as fishing bait...build yourself a profitable business.
Even though the types of worms used in a worm farm are not necessarily what you would find out in your yard they are relatively inexpensive and will reproduce so a worm farm could be self-sustaining.
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