Worms for Composting Horse Manure

Here is a question from George:

My wife and I have two horses and 3 compost bins, each 8’x8’x4′. I’ve
been thinking that our compost might be significantly improved by
adding worms, so I’m wondering what your advice might be on this. We
rotate the bins, about 4 months each, so it takes about a year to
complete a cycle. The oldest bin is typically fairly cool, so I think
that it should be able to benefit from worms. Also perhaps bin number
2. Any advice on things to consider, such as the type of worms that
would work best, would be most appreciated.

Hi George,
Sounds like a great situation to me (said Bentley, green with envy! lol).
Pre-composting/aging the manure for a period of time is definitely important, but I honestly don’t think you would need to do it for as long as you have been, once you’ve got the worms involved. The material you have after the second bin is finished would likely be a great starter “bedding” for the worms, but I would likely set up some separate beds for the actual vermicomposting.

Assuming you have some room to do so, setting up long, low-lying windrow beds might work better for vermicomposting. Once you have the worms settled in the starter bedding materials you could likely start layering newer material over top. Rather than waiting even 4 months for the first batch, I’d suggest hot-composting the manure actively for 2 weeks to a month (tops) before layering it on the beds. Add perhaps 1-2 inches of the material every week or so (maybe less frequently early on, until your worm population has grown).

The best all-around choice for worms would be Red Worms in my humble opinion. They absolutely LOVE horse manure, so they will do every well in these beds, and help you to produce some very nice vermicompost.

During colder weather (assuming you get some where you are located) you’ll likely want to heap up the beds a lot more – maybe even keep the worms in one much larger heap of manure over the winter. The beauty of the “hot composting” process is that it will help to keep the worms warm and active.

Since you own these horses you will be very familiar with what sorts of “de-wormers” (if any) they are receiving, and what they are feeding on etc. For those of you who are getting your manure from someone else, my bottom-line recommendation would be to do your own due diligence before feeding it to your worms.

To learn more about the de-worming issue you may want to check out this older RWC blog post:
How Harmful are Vermicides in Manure?

Apart from the de-worming issue, there is also the potential for the presence of persistent herbicides. Thanks to RWC follower, Laurie S., for sharing these helpful links relating to the topic:

Killer Compost Reports
Use a Simple Compost Test to Avoid Contaminated Materials in Your Garden
Killer Compost Update: Herbicide Damage Still a Major Problem

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    • John Duffy
    • March 6, 2013

    3 8′ bins & 2 horses to supply them…Sounds like a beautiful combination.
    Definitely, go with red worms!

    • Meranaldar
    • March 7, 2013

    Those links at the end are rather scary, I hadn’t known about that.

    • Jennifer
    • June 26, 2014

    How long should manure be aged before it can be fed to worms? And how to you harvest castings in larger worm compost piles?

    • Bentley
    • June 30, 2014

    Jennifer – if manure is allowed to sit outdoors for a month or two it should be in good shape, but it really depends on the manure and on the environmental conditions. Horse manure, for example, can likely be “ready” for worms more quickly than this. Also – very important to note that the planned use will dictate the aging period as well. If it is going to be a base habitat material in a bed, you should age for longer. If a food material (once safe habitat established), it can be added basically “fresh” (assuming system with excellent air flow – and layering on top).

  1. We live in the North Wales mountains and previously we had four horses, but now retired, just have one warm blood. We bed our horse on wood shavings and this is cleaned into a trailer which sits out in the rain and is emptied into our muck heap once a week. The heap is 12 feet x 10 feet and about four feet deep and if you open up the top of the heap where the fresh manure is added it is rich in red worms. These are naturally occuring and not added. We do not turn the heap, but just keep piling on new every week. Every year we dig our garden compost from the bottom of the heap. This is rich black gold for the organic garden and is full of worms. The heap is surrounded by a wide margin of nettles that feed on the run off. These are cut twice a year and added to the compost bins in the garden and also used to make nettle tea. I can send you photos if this would be of interest. There are so many worms in the muck heap that we also collect these worms for our our compost toilet and the wormery that sits outside the kitchen door. Thanks to our muck heap we have never had to buy compost worms!

    • Bentley
    • August 17, 2017

    Fantastic, Dawn!
    Can’t beat horse manure for raising Red Worms as far as I’m concerned. 😎

    • Denise Wood
    • July 13, 2021

    Do red worms naturally occur in horse manure?

    • Bentley
    • September 1, 2021

    Hi Denise
    I always hesitate the word “naturally” when it comes to Red Worms, since they are so closely associated with human activity – but yes absolutely, it is not uncommon for old manure heaps to end up with populations of Red Worms in them, especially in temperate regions. No guarantees though – they need to end up introduced somehow.

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