Horse manure: An easy guide to composting

Catch me if you can ... the odd donation straight onto the shovel saves some of the back-breaking work.
Catch me if you can … the odd donation straight onto the shovel saves some of the back-breaking work.

Once, when many families had their own vegetable gardens and compost heaps, there were plenty of takers for horse manure.

Horses doing their business on suburban streets were rarely a problem, because plenty of householders were prepared to race out with a shovel to collect the bountiful baubles.

Horse manure contains plenty of fibre, making it an excellent soil conditioner. However, it doesn’t rate right at the top of the Pantheon of Poo. That honour belongs to chicken manure — indeed, any bird droppings.

Emeritus Professor of Soil Science John Walker says bird droppings are top of the heap for good reason. Horses — indeed all mammals — produce both urine and dung. Mammals secrete most of their nitrogen, potassium and sulphur through their pee, meaning their droppings are almost always deficient in these key elements.

Birds, on the other hand, excrete through one hole only, meaning all these essential exhaust nutrients are rolled into one neat product.

Horse dung may have its shortcomings, but it has also received some bad press. Sadly, society now moves way too fast for the humble horse poo.

The scenario is all too common: A grateful horse owner who is not in a position to use harrows finds a friend to take away a few bags of freshly collected horse droppings. They dig it into their garden, then complain to the horse lover a few months later that it was full of weeds. They rarely come back for more.

Through all this, nobody appears to have told horses that demand for their nifty nuggets has fallen away. They just keep on producing them at an average of 15 or so dollops a day. This has given rise to what economists call a glut. And, to use business parlance again, there’s nothing worse than an oversupply in a bearish market.

Horse dung has been much maligned because people are bypassing the one crucial step that every keen vegetable gardener knows about: Composting.

Scooping poop: if harrowing isn't an option, you face the fun job of collecting the dung. The challenge is then to find something useful to do with it.
Scooping poop: if harrowing isn’t an option, you face the fun job of collecting the dung. The challenge is then to find something useful to do with it.

Composting is the process whereby naturally occurring microbes break down organic matter. A perfect compost is a soil-like material rich in nutrients and full of roughage which, when added to the garden, improves soil structure and plant health.

The critical thing is overcoming the weed problem. Yes, seeds do pass intact through a horse’s digestive system and will grow if given the opportunity. No self-respecting weed seed would ignore the opportunity provided by anyone who digs them straight into the soil.

The solution is heat. Your consummate composter is aiming to fry those pesky seeds. One of the byproducts of composting is heat, and, if enough is created for long enough, it will kill any seeds and pathogens, providing you with a weed-free compost.

Professor Walker says 80deg Celsius is considered the mark at which you’ll achieve this. However, he says it is not always easy to achieve, and some trial and error may be required to get your composting on a roll.

So what do you need to do?

Create a heap that’s got the right balance of material, moisture, and any added nutrients to encourage healthy growth in the number of micro-organisms that will compost it. Crucially, it needs to be big enough for the heat produced by this process to get to a critical temperature, and stay there for two, even three weeks. You’ve also got to allow air to get to the heart so your composting will occur with air (aerobically) and not without air (anaerobically).

If your heap develops an unpleasant smell, you should turn it immediately.

The unpleasant smell can attract flies that may lay eggs in your heap.

The usual cause is overwatering, or perhaps you didn’t pay enough attention to the layering of the material when you built it. The heat generated in turning the heap should be enough to kill any fly larvae.

If everything goes well with your heap, you should be creating pathogen-free compost. However, to be safe, you should always wear rubber gloves and a mask to reduce the chances of inhaling anything unpleasant. Better safe than sorry.


Let’s assume you’re not really wanting to invest in building or buying compost bins, nor be too scientific about how much fertiliser to add. After all, we’re making compost, not baking a cake!

Pick an area well away from anywhere where odour might be a problem. No neighbour wants a compost heap under their kitchen window. Having said that, a well-built heap should not generate an unpleasant smell.

You’re going to build a heap with a base about 2m across. Don’t put any covering on the ground, as worms and microbes will be prevented from entering your heap from the earth. Ideally, you need room beside it for a second, third, even fourth heap, for reasons we’ll explain later.

If you’ve got some old netting around, form 2m rings with that to contain your heap. You’ll get a better-shaped pile that way, with a bigger heart, which is where the greatest heat will accumulate.

Start shoveling in your horse manure. You’re aiming for a final height of over a metre. You need not build it all at once, but remember that the high temperatures you need won’t be achieved until your pile has a decent heart.

Build an even layer of about 15cm. If it’s dry, get your hose and spray water on until the dung is damp, but not soaking wet. If it’s too dry, the composting process will be slowed and the big heat build-up you need just won’t happen.

Get some general-purpose fertilizer, preferably with a healthy level of nitrogen, and sprinkle a handful over the dung. (Professor Walker’s personal favourite among general fertilisers is Nitrophoska Blue Extra). Eliminate fertiliser at your peril: A shortage of nitrogen is a common cause of slow or ineffective composting.

Now you need a layer of green matter. Lawn clippings are great, but you can use leaves, hedge clippings, vegetable scraps, old hay and the like. This layer should be a little deeper, as the final heap needs to be at least 50 per cent green matter.

Then repeat the layer of horse manure and a sprinkling of fertilizer, paying attention to the moisture content as you go.

If you’re tempted not to add any fertiliser, bear in mind that any deficiencies in your soil will show in your plant matter as well as your horse dung, and, ultimately, your compost. It’s a chance to break that cycle.

A sprinkling of fertiliser as you go, preferably one with a high nitrogen content, will help speed up the composting process and improve your end product.
A sprinkling of fertiliser as you go, preferably one with a high nitrogen content, will help speed up the composting process and improve your end product.

If you’re putting in old stable bedding material, you’ve scored a bonus. Contained in this will be urine, which is rich in potassium, nitrogen and sulphur, so you may not need to correct for any deficiencies. However, if the stable material is sawdust or wood shavings, these use large amounts of nitrogen in breaking down and will nearly always create a deficiency. This being the case, add a rich nitrogen-based fertilizer as you go.

Some people like to add sprinklings of lime to their compost heap. This lowers the acidity, creating a better environment for the microbes to multiply. Others throw in a few shovelfuls of dirt to seed the heap with the right naturally occurring soil microbes

Horse manure, being quite light and fibrous, will help encourage all-important airflow through the pile. The heat generated by your pile rises and this encourages cooler fresh air to be sucked in from the base. Some people help air to get to the centre of their heap by drilling holes in a length of PVC pipe and placing it upright in the middle of their heap.

An even simpler way is to get a strong stick or crowbar and make three or four ventilation holes. See if you can push right to the bottom, work it around a little, and withdraw it carefully.

If all goes well, the centre of your heap should start composting rapidly. If the process seems sluggish, chances are your heap is lacking in either nitrogen, water, or both.

If possible, cover your heap with old sacks or horse covers. These will help retain heat, keep it from drying out, and prevent your heap from getting too wet from the rain.

Correct moisture is critical for success. Too much and you run the risk of your heap staying too cool and producing gloop. Too little and the whole process will be slowed and, again, you’ll have too little heat. If you can pick up a handful and squeeze water out, your heap is too damp. If it’s getting too dry, remove your covers and add water. Some trial and error will be needed to get it just right.

By now, your heap will be composting furiously in the centre, with air-breathing microbes working day and night on your behalf.

The outside won’t be composting near as well, as the heat cannot build up the same.

You thus need to turn the heap three or four weeks after you built it. This is why you’ve placed it somewhere with space beside it.

You shovel the heap across, ensuring that the outside of the old heap forms the inside of the new one. While doing this, make sure the material is not too dry, and add water if necessary. The material should now be much darker and showing clear signs of breaking down.

A mix of horse manure, grass clippings, and old hay well on the way to an excellent finished product. It's light, with plenty of fibre, odour-free, and packed with plant nutrients.
A mix of horse manure, grass clippings, and old hay well on the way to an excellent finished product. It’s light, with plenty of fibre, odour-free, and packed with plant nutrients.

Get your stick or crowbar and create new ventilation holes, cover it again, and the process will continue in earnest. About six weeks later, your magnificent compost will be ready to unveil to the world.

The results will be even better if you turn the heap a third time, at intervals of three or four weeks, but if you provide the right mix and conditions, you should get useable compost with one turning. Essentially, the more times you can turn it at these intervals, the better the end product. If you’ve got a tractor and bucket, you’ve got no excuse.

If you can’t use your compost straight away, keep it covered and a little damp.

So what should you do with your compost? Let your friends marvel at your creation of odour-free, fibre-rich living earth. Many will be so impressed they’ll want some for their own gardens, but only after they’ve gathered some of the raw material from your paddocks for the next batch!

Finally, a reminder that the dung you take off a paddock is gradually robbing the soil of its nutrients. Don’t forget to fertilise, even if you lease your paddocks. Otherwise, it’s your horse you’re shortchanging.

Is horse manure full of weeds?

The question is so important, that scientists in the United States have been given $NZ150,000 to investigate the question.

The heart of your compost heap needs air. The best thing to do is to get a crowbar or a strong stick and make several holes, preferably pushing to the base of the heap.

Most people who have ever dug fresh horse manure into their garden, only to be confronted by a sea of weeds, might consider this money wasted. But the question is important, with more than 700,000 horses a year crossing into national parks each year in California alone.
Authorities in the US are worried that horses taken into parklands and forests for rides might be responsible for the spread of invasive weeds. Concern about this growing problem is such that some states already require horse owners to feed their animals expensive certified weed-free feeds before using public lands.
A California university has started a year-long scientific study to get some answers. The question is not whether weeds and grass sprout from horse dung — rest assured they do — but rather whether the invasive weeds that pose the greatest threat, such as yellow star thistle, grow from the dung.
Preliminary findings indicate that horses may not be as big a culprit as first thought. Biology students collected horse-manure samples from paddocks and national parks. They mixed them with weed-free soil and left them in pots in a university glasshouse free of weed contamination.
Of 90 pots, 34 plants germinated in 21 of them. The most common plant was ryegrass, but several other plant species were identified. However, none of them was on California’s list of noxious and invasive weeds.
Regardless of the final results, expected early next year, halting the spread of weeds is considered nearly impossible in any case, with seeds able to be carried by the wind, and eaten and excreted by birds. They can also travel on animal fur, and be carried into wilderness areas on vehicle or mountainbike tyres, or on the soles of boots.

First published on on June 25, 2006

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9 thoughts on “Horse manure: An easy guide to composting

  • June 2, 2013 at 8:46 am

    Many thanks. Very helpful. Just had about 90 tons of horese manure delivered to our allotments in Liverpool (U.K.) and you give good advice. I do tend to add lime (ground limestone rather than hydrated lime) to my normal compost heap. Hadn’t thought of doing that with the horse manure, but will do so.

  • July 9, 2014 at 7:49 am

    so can i just mix the horse waste in with my vegetable compost. it has lots of grass clippings and leaves. or should i start a seperate pile of compost for the horse manure. thanks

  • August 13, 2014 at 5:15 pm

    Just add them together.

  • September 4, 2014 at 1:56 am

    I’ve just been given some newish horse manure in plastic bins with lids..can I leave it in them to compost as its a bit whiffy and I don’t want flies everywhere..or is it best tipped out/mixed with other stuff..I had thought of top dressing as have very claysoil but its too smelly/hot yet..

  • February 20, 2015 at 6:03 pm

    What would adding a 1000 worms do ? I am trying to make it the most fabulous, I have mini (5) horses and need to do something with the poop but am interested in worm posting too.

  • December 7, 2016 at 12:33 pm

    I am composting with horse manure, oak leaves & grass, but I have no heat…What do I need to do?

  • September 7, 2017 at 6:20 am

    “Potassium 2 phosphate” you can buy online -“ ” good for flowering promotion.
    I don’t know about Nitates if one does not have a farming licence – easy to make explosives !.

  • March 24, 2021 at 5:18 pm

    Remember, if you don’t have fertiliser, you can use urine. It’s sterile and a great source of nitrogen.

  • August 27, 2021 at 5:30 pm

    Is Horsie Pooh’s soaked in water for about 2 months good compost ?


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