Using Worm Bin Leachate

An interesting question from Jake:

I am confussed. I see people s[ell] worm tea and stuff and
that is the reason i bought a [w]orm factory thing. But the other day i
drained a little bit of the worm tea mixed it with a little bit of
water and sprayed it on my plants. My pomagrante tree it seemed over
night got these yellow color to some of the leafs?

Is there a wrong way to use the worm tea? i even saw one website that
said it was toxic and not to use the worm tea liquid on plants. What
is the deal?

Hi Jake,
This is an excellent question – thanks for writing in.
I’ve written about this topic numerous times, but it’s definitely one that deserves to be revisited from time to time.

Unfortunately there seems to be misleading information provided by some worm bin manufacturers (and website owners). The terms ‘worm tea’, ‘worm compost tea’, ‘castings tea’, or ‘vermicompost tea’ should actually refer to the liquid fertilizer created by steeping (soaking) quality castings/compost in water (often aerated) for a period of time. The problem is that many people refer to the liquid that drains out from a worm bin as ‘worm tea’, when the proper term for this is actually ‘leachate’.

Obviously, we’re only talking about words here so it probably seems like I’m splitting hairs, but keeping the distinction between these terms is actually quite important. While leachate can certainly have value as a liquid fertilizer (especially when drained from a mature worm bin), it should be treated with a lot more caution than good quality worm tea. As water passes down through a worm bin it can pick up all sorts of unstable metabolites (various products/intermediates of the decomposition process) – if for example, you can some fairly anaerobic zones in your worm bin, you can end up with various phytotoxic (plant harming) compounds in your leachate.

Finished composts are much better to use for worm tea creation because they are much more uniform in composition, and the vast majority (if not all) the potentially harmful compounds have been converted into something more stabilized. The microbial community present in these materials tends to be more beneficial as well.

Again, I’m not trying to say that leachate is “poison” and should never be used – I just recommend taking some extra steps, or at least using it with caution. I would probably dilute it and aerate with an aquarium air stone before using it myself. You can probably get away with using it outdoors and with hardy plants, but I certainly wouldn’t recommend putting it straight on houseplants or using with plants that tend to be a little temperamental.

Anyway – I hope this helps to clarify things for you a little, Jake.

Written by Bentley on July 18th, 2009 with 12 comments.
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