How long should horse manure age before applying it to my flower and vegetable gardens? How much should I apply?

Material that has decomposed adequately will be brown and crumbly. It will have a fresh, earthy smell. The pile will also no longer heat up when you turn or mix it. When you examine the pile and it has reached this point, it can be used in the garden. There are several factors that will affect how quickly the manure will reach this point and how much you can utilize around your garden.

1. Does it contain bedding? Manure that contains sawdust/wood chips will decompose slowly because of the high carbon content of the bedding. If your horse manure includes wood chips or sawdust, consider layering the material with grass clippings (a good nitrogen source) to speed the process. Manure alone or with straw will decompose readily on its own.

2. Management. Manure that is piled and left alone will decompose slowly. This can take three to four months if conditions are ideal. It can take a year or more if the starting material contains a wide carbon:nitrogen ratio (as is the case when manure contains wood chips). If you pile the material and aerate it by sticking in pipes (see the publication at the end of this answer) and/or turning the material often, you can reduce this time to as little as eight weeks. This aerated process is commonly called composting. It has a number of advantages over stockpiling manure and allowing it to decompose unmanaged:
– You can use the product sooner.
– The heat kills most weed seeds and pathogens (making it safer to apply to vegetables).
– The end product will be more consistent.

3. Application to the garden. If it is to serve as a mulch around the flowers, it can be applied from 1 to 3 inches thick. This will suppress weed seed growth and help conserve moisture around the flowers. Compost does contain nutrients for the plants, but they will release fairly slowly. Fertilize the flowers as you normally would early in the season. Later on, you can fertilize if it appears the plants need it.

If you apply manure compost to your vegetable garden (about one pound per square foot maximum), make sure it is applied at least 60 days before you harvest the crop. You will still probably need to apply fertilizer as you normally would, especially early in the season. If you continue to apply the manure compost over a number of years, you will be able to gradually decrease your fertilizer use.

Some additional reading on horse manure composting is at: Composting Horse Manure.

How do I make manure tea to feed my tomatoes? How long do I wait before using it, & how do I dilute it?

Gardeners frequently use liquid manure (they call it “manure tea”) and every gardener does it differently. The most common process is to take a shovel full of composted manure (raw or fresh manure should not be used on edible crops) and place it into a container. Fill the container with water and let it sit. Some gardeners pour off the brown liquid (the “manure tea”) after a few days, others let it sit for a month or more.

Diluting the manure tea is accomplished by adding water until the mix is light brown in color. Until you become experienced at it, I recommend that you take the diluted mixture and apply to only one plant. Wait for a couple of days and check the plant for signs of scorch or burning. If the plant does show those signs, you need to dilute the manure tea even more. If the plant is fine, then it is safe to apply around your other plants.

Some gardeners use foliar application–that is spraying the manure tea directly onto the plant itself. This is not recommended for edible crops because manure can contain pathogens and cause illness if the pathogens are still on the crop when eaten. Using composted manure will greatly reduce this risk, but not eliminate it entirely. A good article to read about pathogens and using manure on food crops is:
Manure and Compost Utilization on Fruit and Vegetable Crops

Recommended websites to visit to learn more about composting manure are:
University of Rhode Island Healthy Landscapes or Composting Manure

Jill Heemstra, University of Nebraska