How and When to Add Manure to Garden Soil

Adding Manure to Your Garden
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Manure refers to solid and liquid animal waste. It often comes with some of the bedding material (straw, hay, sawdust) mixed in. Odd as it seems, animal manure is an organic material that is often used to improve garden soil.

Why Use Manure

Alone or added to compost, manure improves the soil's texture with the bonus of adding some nutrients to the soil too.

You can use manure from just about any farm animal and even some exotic wild animals. Cow, sheep, horse, and chicken manure are the most popular varieties, but there are several more. Cat, dog, pig, and human manures are not used in gardening, as they have the potential to carry pathogens that are harmful to humans.

How and When to Add Manure to Your Garden

This wonderful free resource does require some patience, though. Fresh manure is high in nitrogen and ammonia and can easily burn plants if it comes in contact with them.

Fresh manure can also contain bacteria that would contaminate any edible plants growing in or near it. You need to compost manure or let it rot, for at least 6 months to a year, before it is ready to be used in the garden. You can throw the manure in a compost pile or let it rot on its own, although it will have a strong odor if you do this.

You can reduce the odor of fresh manure by allowing it to dry out and mixing in or covering it with a brown composting material such as dried leaves or shredded newspaper. The odor is strongest when manure is kept in anaerobic conditions, which is why mixing it in with compost is a better practice than simply letting it rot on its own.

Some farmers will top their fields with fresh manure in the fall and let it age through the winter. This works, but it's not the most efficient use of manure. If you choose to try this method, the USDA National Organic Program (NOP) recommends you apply fresh manure at least 120 days before harvest of vegetables that come in contact with the soil (root crops, low-growing leafy crops) and at least 90 days for vegetables that don't come in contact with soil, such as tomatoes and peppers.

Some Other Considerations

  • When you go to pick up manure, head for the oldest pile they have. It may have already gone through a few months of rotting. That means you can use it sooner and it shouldn't smell as foul as the freshest manure.
  • Don't be afraid of manure piles with a lot of bedding in them. The more bedding there is in fresh compost, the faster it rots.
  • Ask if the manure has been sprayed with anything. Some farmers will use pesticides on manure piles to keep the flies in check.
  • Bagged manure costs considerably more, but it is already composted for you and ready to use.
  • Use rotted manure as you would compost. Plan on amending your beds with it annually.
  • The strongest smelling manures are chicken and rabbit, while the mildest is from sheep. Sheep manure is also drier and easier to spread.

Nutrient Content of Common Animal Manures

Animal N-P-K Ratio
Chicken 1.1-0.8-0.5
Cow 0.25-0.15-0.25
Horse 0.7-.0.3-0.6
Llama 1.5-0.2-1.1
Rabbit 2.4-1.4-0.6
Sheep 0.7-.0.3-0.9

Where to Find Sources of Manure

Farms and zoos are your best bets for finding free manure, however as gardening becomes more popular, farmers and zookeepers are wising up and selling their manures as an additional source of income. Even if they aren't giving it away, it is still quite inexpensive, especially if you have a truck to go and pick it up yourself.