Manures can make an excellent fertiliser

When we think about how to compost horse manure, we might think about how to compost any manure.  Most manures can make an excellent fertiliser and horse manure is no exception. So long as the manure is from a happy and healthy animal, it’s usually safe to use on our gardens.

Generally manures are  full of nutrients, microorganisms and partially digested organic matter. Manure feeds the creatures and microorganisms in our soil, it improves soil structure and it’s a vital ingredient in my edible garden.

It’s also relatively available in its natural form. This is particularly the case if you can take a drive to a rural or semi-rural area. However, there are some things that we need to consider when planning to or actually using horse manure.

Hot composting horse manure

We can compost horse manure in two ways: hot or cold composts. Hot composting is fairly hard work and most home gardeners don’t have the physical resources to do it properly. To build an adequate hot compost we need at least one cubic metre of raw materials. That’s a big ask for most people. For that reason, we’ll discuss cold composting here and cover hot composing in a separate blog.

Cold composting horse manure

In my garden I have several compost piles. One or two are hot, at least one is cold and it contains a lot of other materials like lawn clippings, garden off cuts etc.  One of my composts is a dedicated cold compost horse manure pile.  That’s the best way I’ve found when we’re thinking: how to compost horse manure.

The dedicated horse manure pile will become compost. Originally I placed the horse poo on the bare earth, covered it with sugar cane mulch, watered it and it started breaking down into compost. That generally takes between two and three months. The quality and quantity of soil life in the manure pile will speed up or slow down that process.

If you haven’t got sugar cane mulch, dried leaves, or dried hay or that type of material should do well. So long as its dried and brown in colour. To learn more about composting materials, click here.

The more life, the quicker the task.  That’s a key element for composting horse manure. I got rid of my worm farm when I realised that I could maintain the worms in a healthy habitat by replenishing the horse manure pile.  Creating a healthy microbial habitat is also a key element in creating healthy soil.

The dedicated horse manure pile is constantly full of microbial and worm life and I never fully deplete that pile of all its compost.  I always leave some manure for the worms and microbes and this ensures they have plenty to eat and a sanctuary in which to live.

To replenish the pile, I simply add more manure, cover that with mulch and make sure it stays moist and never dries out.

Do we need to turn our compost?

Sometimes we might wonder how to compost horse manure if we don’t turn it?  If we’re making a hot compost, then yes, we’ll want to turn it. Hot composts will become pathogenic very quickly if we don’t turn them. Click here to learn more about hot composting.

Turning compost increases air flow ensuring the microbes in the compost have enough oxygen to breathe.

However, cold composts are different. Unless we have significantly large piles of horse poo and it’s all mostly fresh, our horse manure compost pile will tend to perform like cold compost. For that reason, we generally don’t need to turn it.

In fact, once there are worms in it, I certainly won’t turn a compost. Turning soil or compost with worms in it harms the worms and also destroys their tunnels and pathways – their homes. If we want soil and if we want compost then we need to befriend our soil inhabitants.

Therefore, generally, turning a cold horse manure compost pile is more destructive than fruitful.

Horse manure is hot and full of nitrogen

Horse manure is hot and that means it has quite a bit of nitrogen in it. Have you ever mowed the lawn and piled up the clippings? Have you noticed how hot it gets inside that pile? That’s caused by thermophilic bacteria who thrive on a high nitrogen diet and high temperatures. Temperatures can reach upward of 65* Celsius (149* Fahrenheit) in some composts. I’ve seen poorly maintained composts burst into flames due to this bacteria.

We shouldn’t put fresh or uncomposted horse manure on a garden that has plants in it. The nitrogen content is likely to burn plants. Plant leaves may wither and brown and result in general plant stunting. Likewise, most of the nitrogen in the poo isn’t readily available to plants.

The nitrogen needs to be converted to nitrates to be plant available. Microorganisms are the creatures responsible for that conversion. Therefore, it’s microorganism that will turn our hot horse poo into cool compost.

Horse manure is usually fairly high in lots of nutrients

Horse manure is usually fairly high in nutrients. This is probably because of the anatomy of a horse. For example, cows have four stomachs and produce fairly mild manure.   Horses have one stomach and produce richer manure – it has more nutrients and is less ‘processed’.

It’s also probably because horses tend to receive supplemental feeding high in nutrients. When we buy horse manure on the side of the road it’s often supplied in the feed bags. Those bags usually list the nutrient components of the feed. It’ll show the nitrogen, calcium, iron, copper, sodium etc. Because horse manure is partially digested, we know that their manure contains a lot of those elements.

That’s a key reason why quality composting works in organic gardens. If our compost sources are diverse it’s more likely we have the full range of nutrients. Microorganisms make those nutrients plant available. The same is true for manures.

If a horse (or any animal) eats only grass in a paddock then the manure will reflect the nutrient make up of the grass. If the soil that grass grow in is nutrient deficient, then so too will be the manure.  So it’s a matter of: what goes in, must come out! However, that also applies to weeds, hormones and medicines.

Horse manure can contain weeds

When we look closely at horse poo, we can see the individual blades of grass in it. We can also see seeds: some of which are from weeds. If we’re going to hot compost our horse manure then this can effectively treat the seeds.  The heat treatment prevents them from germinating. However hot composting is an art and eliminating all weed seeds is tricky.

For that reason, with our cold composts, we need to be vigilant when we apply composted manure to our gardens. We need to watch out for new weeds popping up.   However, having said that… I haven’t experienced an introduced weed problem from my composted horse manure.

Despite cold composting most of my horse manure, it seems that composting for 3 months may be sufficient time to allow microorganisms and worms to consume all raw material in the manure and this seems to include weed seeds.

Horse manure can contain hormones and medications

Animal welfare science suggests that happy and healthy animals tend to have relative freedom.  That means they are free from restrictive controls and containment.  They are free to exhibit normal animal behaviours; and they are in contact with other animals of their species.  Social isolation, caging and/or significantly containing an animal causes stress and stress leads to illness.  The onset of illness tends to require medications.

Where animals have been given medications or hormones, those medications or elements of them get excreted in urine and faeces.  Therefore, if a horse has been medicated or given hormones or steroids, then those elements are likely to show up in the manure as well.

This is a fairly important factor to consider given the high degree of animal containment and caging in our society.  When we purchase a manure based product from a retail outlet or bulk manure a landscape supplier, are those manures from happy or suffering animals?  Have those animals been given antibiotics and medications?

The science reveals that composting can eliminate some hormones and medications.  Some composting reduces these elements and others may not be transformed at all for some time.

This means that where we source our manure from is important if we don’t want to transfer those chemicals to our soils and our plates.  Therefore, when sourcing manures, it’s probably a good idea to find happy, healthy, unmedicated animals.

So, that’s how to compost horse manure that’s free from harmful pathogens, chemicals and detrimental karma!


Anonymous · March 1, 2020 at 3:37 am

Is it true that most female horses, healthy or not are given synthetic estrogen regularly? Can this estrogen be taken up by plants. I really want to figure this out.

    Anonymous · July 7, 2020 at 10:16 am

    Ask the owner rom whom you get the manure. Most people do not give hormones to their female horse. Pregnant horse urine is full of natural estrogen, not synthetic.

Phil · October 20, 2019 at 11:27 pm

Are you concerned about herbicides in the feed that horses can eat.

Anonymous · May 13, 2019 at 7:13 am

Thanks for the information. What do you suggest to mix with the horse manure instead of sugar cane mulch that we don’t have access to.

    Amber Hall · June 4, 2019 at 12:07 pm

    Dry leaves, dried hay… the dried ingredients such as the mulch, leaves etc make the carbon element. This is a key element for microbes who can’t survive in a nitrogen rich environment.

Lyn. · February 3, 2019 at 12:55 pm

Excellent information. Thank you. I use horse manure from the local trotting stables. I take soil forming a hole in the lawn area where we removed a liquid amber tree some years back.Then fill with manure and grass clippings mostly. One does not know what has been in the soil previously of course.

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