How Much Manure Should You Add? Types and Garden Tips

Ratio of Soil to Fertilizer From Cows, Horses, or Chickens.

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, or sawdust) mixed in. Animal manure is an organic material that is often used to improve garden soil because of the nutrients it contains.

Manure Benefits

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 wild animals as long as they are herbivores (plant-eating animals). Cow, sheep, horse, and chicken manure are the most popular varieties, but there are several more. Chicken manure is also known as "black gold" for a garden. Cat, dog, pig, and human manures are not used in gardening, as they have the potential to carry pathogens that are harmful to humans and the specific nutrients may not be beneficial to plant growth.

How Much Manure Should You Use?

It helps to know how much manure to use in your garden because too much manure could damage your plants because some types have more salt content in them than others, for example. Use 20 to 30 pounds of rotted or composted manure for every 100 square feet of your garden. The higher the nitrogen in the manure, consider using less of it.

Here is an indication of the approximate amounts of cow or poultry manure needed based on a garden size of 100 square feet.

Type  Application Rate for 100 Square Foot Garden 
Dairy cow 200 pounds composted manure
Chicken/Poultry 70 pounds composted manure

How to Add Manure to Your Garden

This free resource of garden nutrition 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 could contaminate any edible plants growing in or near it. You need to compost manure or let it rot for at least six 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 it this way.

To reduce the odor of fresh manure, allow it to dry out and mix in or cover 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.

When to Add Manure

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 the harvesting 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.

Manure Selection

  • 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

Though you are not buying packaged manure, it helps to know that NPK on a fertilizer package stands for nitrogen, phosphorus, and potassium (K), Manure content is generally based on its nitrogen content, but it also contains quite a bit of phosphorus and potassium, too. It's recommended that you have your soil tested to make sure you use the right fertilizer for your garden's nutrient needs. Here are the NPK ratios for the most popular types of manure.

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

Sources of Manure

Farms, small horse stables, and zoos are your best bets for finding free manure. However, as gardening becomes more popular, farmers, stable owners, and zookeepers are beginning to sell 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.

Article Sources
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  1. Choosing a Soil Amendment. Colorado State Extension

  2. Fertilizing a Garden. Texas A&M AgriLife Extension Service.

  3. Using Manure in the Home Garden. Wisconsin Horticulture.

  4. Here's the Scoop on Chemical and Organic Fertilizers. Oregon State University Extension

  5. Manure in Organic Production Systems. U.S. Department of Agriculture’s Agricultural Marketing Service, National Organic Program

  6. Using Manure in the Home Garden. Wisconsin Horticulture.