How to Compost Manure: A Beginner’s Guide

Here’s how we compost manure at Green Acres using passive composting (also called cold composting). This is the easiest method and requires minimal effort – perfect if you’re just getting started with composting manure or if you have a busy life and can’t tend to a compost pile regularly.

If you’re trying to decide which type of manure to use, see my guide on Composting Animal Manure: Complete Guide to Using Chicken, Cow, and Horse Manure in Your Garden. For information on when to apply your finished compost throughout the year, see [LINK: When to Add Manure to Your Garden: Seasonal Timing and Application Methods].

Why Compost Manure Before Using It in the Garden?

Fresh manure (except rabbit manure) needs to be composted before you use it in your garden for several important reasons:

• Prevents plant burn: Fresh manure, especially chicken manure, contains high levels of ammonia and nitrogen that can literally burn plant roots and kill plants
• Kills pathogens: Composting eliminates harmful bacteria like E. coli and salmonella that can contaminate vegetables
• Reduces weed seeds: The composting process, especially hot composting, kills many weed seeds present in manure
• Stabilizes nutrients: Composting converts the nutrients in manure into forms that plants can use gradually rather than all at once
• Improves texture: Composted manure is easier to work into soil and won’t clump like fresh manure

Two Ways to Compost Manure: Passive vs. Active

There are two main ways to compost manure, and both work well. The difference is in how much effort you want to put in and how quickly you need finished compost.

Passive (Cold) Composting:

• Pile it up and let time do the work (6-12 months)
• Requires minimal effort
• Works great for most home gardeners
• This is what I do at Green Acres

Active (Hot) Composting:

• Turn the pile regularly to maintain high temperatures (145-165°F)
• Kills more pathogens and weed seeds faster
• Composted in 2-4 months instead of 6-12
• Requires more work and monitoring
• Better for horse manure to kill weed seeds

Both methods work—passive composting just takes longer.

How to Compost Manure Using Passive (Cold) Composting

This is the method I use at Green Acres. It’s simple, requires almost no work, and produces excellent compost.

1. Start the compost pile:

When we clean out the barn (usually once or twice a year), everything goes onto a pile away from the garden. This includes all the manure mixed with bedding (straw, wood shavings, or hay).

Location tips:

• Choose a spot at least 50 feet from your garden to avoid contamination
• Pick an area with good drainage so the pile doesn’t get waterlogged
• Partial shade is ideal—full sun can dry it out too much, full shade can keep it too wet
• Make sure it’s accessible year-round for adding material

2. Let it compost:

That pile sits for at least 6 months, preferably a full year. I’ll turn it once or twice if I think about it, but honestly, time does most of the work. The manure and bedding slowly break down through natural decomposition.

What’s happening in the pile:

• Beneficial bacteria and fungi are breaking down organic matter
• The pile may heat up some (though not as hot as active composting)
• Rain and moisture help the decomposition process
• Earthworms and other organisms move in and help break things down

3. Check if it’s ready:

Properly composted manure shouldn’t smell like ammonia or fresh manure. It should smell earthy and look dark and crumbly. The original materials should be unrecognizable—you shouldn’t see distinct pieces of straw or manure anymore.

The three tests for finished compost:

• Smell test: Should smell like rich earth, not ammonia or manure
• Look test: Should be dark brown or black and crumbly
• Texture test: Should break apart easily in your hands

4. The safety margin:

When in doubt, let it compost longer. You can’t really over-compost manure (within reason), but you can definitely under-compost it and risk burning plants or introducing pathogens.

How to Compost Manure Using Active (Hot) Composting

Active composting requires more work but gives you finished compost much faster. This method is especially good for horse manure because the high heat kills more weed seeds.

1. Build your pile correctly:

• Start with a pile at least 3 feet x 3 feet x 3 feet (this size is needed to generate and hold heat)
• Layer manure with carbon-rich materials (straw, leaves, wood shavings) in roughly equal amounts
• The pile should be moist like a wrung-out sponge—not dripping wet, not dry

2. Turn the pile regularly to maintain high temperatures:

• Use a pitchfork or compost aerator to turn the pile every 1-2 weeks
• Move material from the outside edges to the center where it’s hottest
• The center of the pile should reach 145-165°F
• You can use a compost thermometer to monitor temperature, or just feel the heat when you stick your hand in

3. Monitor moisture:

• Add water if the pile gets too dry (it should stay moist)
• Turn more frequently if it gets too wet and starts to smell
• The pile should steam when you turn it if it’s working properly

4. Composting time:

• With regular turning and proper moisture, manure can be fully composted in 2-4 months
• Chicken manure may take closer to 4 months
• Cow and horse manure can be done in 2-3 months with hot composting

What About Mixing Different Types of Manure?

You can absolutely mix different types of manure in the same compost pile. In fact, mixing can work well:

• Chicken manure (high nitrogen) + cow manure (lower nitrogen) = balanced compost
• Any manure + bedding (carbon) = ideal composting conditions
• Just compost for the longest time required by whatever manure you’re using

At Green Acres, our “barn dirt” is naturally a mix of cow manure and whatever bedding we’ve used, which creates the perfect carbon-to-nitrogen ratio for composting.

How Much Space Do You Need for Composting Manure?

This depends on how much manure you have:

Backyard chicken keepers:

• A 3×3 foot area is plenty
• One or two annual barn cleanouts will fit

Small farms with a few animals:

• Plan for a 6×6 foot or larger area
• You may want two piles—one actively composting, one being used

Larger operations:

• Multiple large piles in rotation
• Consider a three-bin system: one filling, one composting, one ready to use

Common Composting Mistakes to Avoid

Mistake #1: Using fresh manure too soon. Wait the full recommended time. Chicken manure especially needs 6-12 months with passive composting.

Mistake #2: Making the pile too small For active composting, piles smaller than 3x3x3 feet won’t generate enough heat.

Mistake #3: Letting the pile dry out Decomposition needs moisture. If your pile is dry and nothing’s happening, add water.

Mistake #4: Putting the pile too close to the garden Keep it at least 50 feet away to prevent runoff from contaminating growing vegetables.

Mistake #5: Not mixing in carbon materials Pure manure composts slowly and can smell. Mix in straw, leaves, or wood shavings for best results.

How to Know Your Composted Manure is Safe to Use

Before using your composted manure in the garden, especially in vegetable gardens, make sure it passes these tests:

✓ Time test: Has it been composting for the minimum time for that manure type?

• Chicken: 6-12 months (passive) or 3-4 months (hot)
• Cow/Horse: 3-6 months (passive) or 2-3 months (hot)
• Sheep/Goat: 4-6 months (passive) or 2-3 months (hot)

✓ Smell test: Does it smell earthy and pleasant, not like ammonia or fresh manure?

✓ Look test: Is it dark and crumbly with no recognizable pieces of original material?

✓ Temperature test: (For hot composting) Has the pile cooled down completely after the active composting phase?

Storage: What to Do With Finished Compost

Once your manure is fully composted, you don’t have to use it immediately. Finished compost can be stored:

• Keep it in a pile or bin with good drainage
• Cover it with a tarp to keep it from getting waterlogged in heavy rain
• Store it for months or even years—it just continues to mature
• Avoid letting it completely dry out; keep it slightly moist

The Bottom Line on Composting Animal Manure

Composting manure isn’t complicated. The passive method I use at Green Acres is truly as simple as piling it up and waiting. The active method requires more attention but gives you finished compost faster. Either way, you’re creating one of the best soil amendments you can add to your garden.

Remember:

• Passive composting: 6-12 months, minimal work
• Active composting: 2-4 months, turn regularly
• Ready when: It smells earthy, looks dark and crumbly, and has no recognizable original materials
• Safety: Always compost for the full recommended time, especially for vegetables you’ll eat raw

For more information on which type of manure is best for your situation, check out my Complete Guide to Composting Different Types of Animal Manure, and for timing on when to apply it, see When to Add Manure to Your Garden.