Nitrogen is the most essential nutrient for plant growth and the nutrient whose absence is most likely to limit growth in your garden. Plants also need phosphorus and potassium in abundant amounts. With the exception of manure from rabbits, chicken droppings contain more nitrogen than any other manure source -- over 1 percent compared to about a half percent for other species. Chicken manure also contains above-average levels of phosphorus and potassium levels equivalent to that available from other livestock manures.
In order to safely use chicken manure, you will need to compost it, as fresh manure can harm your plants and pose health risks to humans. Unfortunately, composting chicken manure lowers the nitrogen content, as the manure releases nitrogen-containing ammonia as a gas as it breaks down. However, composted manure provides organic matter, which can improve your soil's ability to retain water and nutrients and loosen compacted soil; fresh manure does not. For best results, incorporate composted chicken manure into the soil three to four weeks before planting. You can also use composted manure to sidedress existing plantings.
Failure to properly compost chicken droppings before using them as fertilizer carries several risks. The high levels of nitrogen for which gardeners value chicken manure also causes salts to form in the soil, which can pull water from your plants' roots, making the foliage appear burned. Manure from pasture-fed chickens may contain weed seeds. Finally, fresh manure contains pathogens that can cause serious illness in humans that consume any fruits or vegetables that become contaminated. At least three months should pass between applying fresh manure and harvesting any edible plants. You can avoid all of these problems by composting chicken droppings before using them.
Because safe use of chicken manure fertilizer requires composting before applying it, diminishing the nutrient content, chicken manure alone may not adequately feed plants that require high amounts of nitrogen or vigorously growing plants. You may need to apply additional fertilizers.