You often read about the merits of the liquid “feed” produced as a by product of a worm composting bin, very often it is praised particularly by the manufacturers of “wormeries” that appear to produce this wonderful liquid, often referred to as “worm tea”, produced like this, worm tea it is most definitely not!
A good quality, well designed wormery will produce very little liquid if it is being managed correctly, this is because worms operate on surface area and allow a good circulation of air into the system, under normal operating conditions the majority of any liquid present will tend to evaporate off, the exception to this is when too much liquid is being added by the owner, this could be in the way of something like wet lettuce leaves, or loads of wet tea bags!
When a wormery is designed on depth and not surface area and is usually constructed out of plastic with no ventilation in the base, it will have very little air circulation and the liquid cannot evaporate, any moisture will condense on the sides of the smooth plastic and run to the bottom, to prevent this from soaking into the bedding and making the whole lot soggy, a grid is usually manufactured into the bin, a few inches above the base, this allows the liquid to drain and collect in this sump, a tap is then conveniently added to allow the liquid to drain off and advised to be used as a plant feed.
Is the liquid any good?
Sometimes it can be beneficial to plants, a lot depends on the maturity of the worm bin, if it has been established long enough for compost and wormcasts to have built up to a reasonable depth and is in good, healthy condition with no nasty smells then the liquid passing through will have dissolved some nutrients present and collected some bugs and bacteria and therefore being added to plants can be beneficial, providing the liquid has been drained regularly and not allowed to collect in the sump and stagnate. If the wormery has not been established long then the liquid being collected is not likely to have much benefit, as there will be no real nutrients and no beneficial bugs and bacteria, a bit like rinsing the waste first and watering the plants after!
Can the liquid be harmful?
Yes it can, if the compost and waste in the worm bin has gone stagnant and smelly this means that anaerobic conditions have set in (anaerobic – without air) this produces a whole lot of different bugs and bacteria (and usually dead worms) and these can be most harmful to plants, this also applies to liquid from a healthy system that has collected in the airless sump for a long time, the advice is to always dilute the liquid and this will lessen the potential harm but does not necessarily eliminate it.
What is the best way to make worm tea?
Proper worm tea is produced in a tea brewer, one of the ingredients being wormcasts or compost and is a subject in itself. A quick but less efficient way is to take a bagful of wormcasts or compost, importantly, collected from a good, healthy system (if it smells offensive in any way – leave it alone) stand the bag in a bucket of water for 24 hours, stir occasionally, drain the
liquid, dilute and use, do not bottle and store.
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