Horse manure

Magic1One of our SA readers wants to know what to do about the weeds that sprout from their horse manure pile, as she is concerned about spreading the weeds through her garden. She also has a problem with millipedes. Interestingly, manure and millipedes have a relationship because millipedes feed on decaying organic matter and they can lay their eggs in faecal matter. Millipedes are related to slaters. See Slaters and earwigs for controlling them in the garden.
Horse manure is often the easiest manure to obtain close to metropolitan areas. We have found horse manure to be a good source of plant nutrients and our miniature Shetland, Magic, works 24/7 to keep up supplies. Small amounts can be fermented in a bucket of water, then diluted, to produce a fertiliser tea for plants that need a boost.
But, adding uncomposted horse manure to the garden can encourage millipedes, slaters and earwigs. This is more common if you use sheet composting for the manure, a process of spreading a layer of manure on an unused garden bed, dampening it and covering it with mulch.
The best way to use fresh horse manure is to put it into the compost heap as it is a good source of nitrogen and generates a lot of heat, but there is a big difference between an active compost heap and a pile of horse manure. The manure should be mixed with dry ingredients such as straw, mulch, shredded newspapers, or dry leaves to create a good nitrogen to carbon balance. The heap should also be turned regularly to aerate the heap because aerobic bacteria require nitrogen, moisture and oxygen to work efficiently. When the compost heap is turned, newly germinated weed seeds get turned into the mixture and provide more organic matter for the bacteria to feed on. In its early stages, the heap should generate enough heat to kill off pathogens and seeds. As the composting process continues, the heap reduces in volume. As it gets cooler, you will occasionally see earwigs, slaters or millipedes in the mix but they are helping to break it down so don’t spray them with anything. When the organic matter reaches a favourable stage, earthworms move into the heap if it has contact with soil, and they digest the decomposing organic matter and turn it into worm castings. The final product, ready to be used on garden beds, is about one quarter of the volume of the original heap, friable, very dark brown in colour, and has a earthy, rainforest smell.
If you just leave horse manure in a pile to break down, it will tend to pack down and anaerobic (without oxygen) composting will occur. This is much slower, and can generate unpleasant smells. A lot of the nitrogen can be lost to the air and other nutrients can leach away when it rains.
To get horse manure to work even more quickly in a compost heap, tip it onto a hard surface and mince it a bit with the edge of a spade, because bacteria only work on the surface area of the ingredients. Producing more surface areas to feed on by chopping ingredients will greatly speed up the process.

6 thoughts on “Horse manure

  1. I have been told today that using stable manure in my compost will kill my worms, (hence your comments above). If I only put manure into my compost bin and leave for several weeks, with leaves, food scraps etc. would I still need to test for presence of chemical additives.I would hate to do the wrong thing by my worms.
    Although worms do not immediately move into compost heaps, Pat, any intestinal worm treatments given to animals are still likely to be active in the manure after the bacteria have finished their work, and are likely to kill your worms. That is why it is wise, when using manures obtained from a source where you don’t know what medication animals have received, to test a sample of manure as described in the comments above before adding it to compost heaps. For safety, manures must be tested before adding to worm farms. – Lyn

  2. What chemical additives (dewormers) might linger in horse manure? I have local horse owners that provide it free, but I wonder whether there may be certain things I should watch out for?
    Gabs, if horses have been treated for parasites the vermicide may still be active in the manure. Vermicides also kill microorganisms in compost. You should always test manure before adding it to worm farms or compost bins by putting a shovelful of damp manure into a bucket, adding a few compost worms, covering the bucket and putting it in a cool spot for a day or two. If the worms are alive, you can add the manure. If any vet treatment has killed the worms, the manure can be mixed with vegetable matter and composted separately. – lyn

  3. May I request for a SDS for cow manure, please.
    If you Google particular brands of cow manure sold( e.g. Bunnings, Richgro)you will find the safety data sheet each company produces.

  4. I want to feed my worms. Is bagged horse manure ok? or is fresh ok too? mainly have access to bagged manure. any suggestions welcome.
    Hi Glen, yes, you can use horse manure as feed in worm farms. Very fresh manure generates a lot of heat, so I’d leave it for a week or so before adding it to the farm. Chopping the ‘nuggets’ with the edge of a spade will make it easier for the worms to eat it as by doing this you increase the surface area of the manure. Worms will eat any weed seeds in the manure, too.
    If you are not sure if the horses that produced the manure have been wormed recently, it is wise before adding the manure to the farm to collect some worms, put them in a bucket with a shovel of chopped manure. Leave it for a day or so to see whether any worming treatment is still active in the manure and has killed the worms in the bucket. If the worm treatment is still active, you can compost the manure instead. – Lyn

  5. You are inaccurate regarding horse composting. Horse manure with just added water will compost after a month under black plastic…turned and watered after 2 weeks. There is no smell and earthworms in particular are prevalent which indicates you are doing it right!…biodynamic compost heaps are only heated to around 30c unlike commercial heaps that tell you to 70c for 3 days…

    Thank you for your input, Peter. Our composting methods are based on Australian Standard 4454 which states that compost heaps that include manures and food waste must be subjected to an internal temperature of a minimum of 55° C. for 3 continuous days before each turn. A mass of 1 cubic metre is considered necessary for the higher temperatures to be achieved. I know from personal experience that a large heap of fresh horse manure and stable cleanings dumped on a dry paddock on a hot day can generate enough heat in about 6 hours to start a grass fire.
    It is true that damp horse manure can compost at lower temperatures, however, this compost will not have been pasteurised. The higher temperatures are required to kill human and plant pathogens and weed seeds, and assist the breakdown of any chemical residues by thermophile (heat-loving) bacteria that are active in temperatures between 45 – 122° Celsius.
    Certified-organic farmers are allowed to compost horse manure by the method you advised, but it must be followed by 2 green manure crops before the area can be used to grow crops for human consumption.
    See Recycled Organics Unit Fact Sheet for details. – Lyn

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