Horse Manure Management: How to Compost It, Spread It and Use It in the Garden

By Gayle Woods Editors Updated 6 min read

Every horse owner eventually faces the manure pile question. A single horse produces several tons of manure a year, and a pile that grows unchecked breeds flies, smells, washes into streams and annoys neighbors. Handled well, the same material becomes a valuable soil amendment for pastures and gardens.

How much manure a horse makes

An average 1,000-pound horse produces about 50 pounds of manure a day, including urine. That's roughly 9 tons a year. A stalled horse adds bedding on top of that, often bringing the total stall waste to 60 pounds or more a day.

In volume, that's enough to fill a pickup truck bed every week or two per horse. Multiply by the number of horses, and it's clear why every farm needs a plan.

Your options

  1. Spread it on fields. Manure is a fertilizer. Spread thinly, it breaks down quickly in sun and wind. The best approach is to compost first, then spread.
  2. Compost it and use it on your pastures, garden or landscaping.
  3. Give it away or sell it. Gardeners often want aged or composted horse manure.
  4. Have it hauled away. Some areas have dumpster or pickup services for manure.
  5. Stockpile it. A pile that simply sits will slowly break down, but it breeds flies and can leach nutrients unless it's covered and well placed.

Most small farms use a combination: compost some, spread some, and give some away.

Why compost

Composting is controlled decomposition. Microbes break down manure and bedding and, if the pile is managed well, it heats up on its own. That heat:

  • Kills parasite eggs and larvae, breaking the worm cycle on your pastures. See the deworming guide.
  • Kills fly eggs and larvae. See how to get rid of horse flies.
  • Kills most weed seeds that passed through the horse from hay.
  • Shrinks the pile to about half its starting volume.
  • Produces a stable, earthy material that's easy to spread and won't burn plants.

How to compost horse manure

Composting needs four things: the right mix of materials, moisture, air and enough mass to hold heat.

Location

  • High, well-drained ground, not in a low spot where water collects.
  • At least 100 feet, and preferably more, from wells, streams, ponds and ditches. Check local rules.
  • Close enough to the barn that you'll actually use it.
  • On a concrete pad or compacted surface if you can, to limit runoff.

Setup

  • Bins: a three-bin system works well for one to a few horses: one bin being filled, one composting, one finishing. Pallets, concrete blocks or wooden boards make simple bins. Each bin should be at least 3 by 3 by 3 feet, so the pile can hold its heat; bigger works better.
  • Windrows: long piles on open ground suit larger farms with a tractor to turn them.
  • Small-scale: for one horse in a small space, a large compost bin or two can handle part of the load.

Managing the pile

  • Mix: horse manure with shavings or straw usually has plenty of carbon. Pure manure with little bedding may need some added carbon such as leaves.
  • Moisture: the pile should feel like a wrung-out sponge. Water a dry pile; cover the pile with a tarp in heavy rain so it doesn't get soggy and lose nutrients.
  • Air: turn the pile every week or two with a fork or tractor, or build it over perforated pipes for passive aeration. Turning moves the outside material into the hot center.
  • Heat: a compost thermometer shows whether it's working. Aim for 130°F to 150°F in the center. Keeping that temperature for at least three days, and turning so all the material gets a turn in the middle, kills most parasites and seeds.

When it's done

Compost is usually ready in two to six months, depending on the season and how often you turn it. Finished compost:

  • Looks dark and crumbly, like rich soil
  • Smells earthy, not like manure
  • Doesn't heat up again after turning
  • Has shrunk to about half its original volume

Spreading manure and compost on pastures

  • Spread compost, not fresh manure, on pastures horses are grazing. Fresh manure spreads parasite eggs and larvae onto the grass.
  • If you spread fresh manure, use it on fields horses won't graze for a while, such as hay fields, or spread it thin in hot, dry weather so the sun kills more eggs.
  • Spread thinly, about a quarter to half an inch at a time.
  • Don't spread on frozen or snow-covered ground, or right before heavy rain. Nutrients wash off into streams.
  • Soil test to see what your pasture needs before you add a lot. See how many acres a horse needs.

Using horse manure in the garden

Horse manure is a good garden amendment. It adds organic matter that improves soil structure and holds water, along with modest amounts of nitrogen, phosphorus and potassium.

A few rules:

  • Use composted or well-aged manure. Fresh manure can burn plants with ammonia, ties up nitrogen as the bedding breaks down, and may carry weed seeds and bacteria.
  • For vegetable gardens, apply composted manure at least a few months before harvest, and keep fresh manure well away from crops you'll eat raw.
  • Work it into the soil a couple of weeks before planting, or use it as a top dressing around established plants.

The herbicide problem

Some long-lasting herbicides used on hay fields and pastures, including aminopyralid, clopyralid and picloram, pass through horses unchanged and survive composting. Manure from horses that ate treated hay can damage sensitive garden plants such as tomatoes, peppers, potatoes, beans and peas for a year or more. Symptoms include curled, twisted leaves and stunted growth.

If you give away or use manure in gardens:

  • Ask your hay supplier whether these herbicides were used.
  • Run a simple test: fill a few pots with a mix of compost and potting soil and plant beans or peas. Plant a few in potting soil alone. If the compost plants come up with cupped, twisted leaves, don't use that compost on a vegetable garden.

Tools that make it easier

Sources

Frequently Asked Questions