Cow manure is a highly effective organic amendment for garden and agricultural soils. This common byproduct of cattle farming, often mixed with bedding material like straw, functions as a rich fertilizer and soil conditioner. Using it safely and effectively requires understanding its composition and following important preparation steps.
Nutrient Profile of Cow Manure
Cow manure is valued for its balanced, slow-release supply of plant nutrients rather than high concentrations. Its composition is variable, depending on the animal’s diet and bedding, but it generally offers a modest ratio of nitrogen (N), phosphorus (P), and potassium (K). These nutrients are released gradually as the material decomposes, providing sustained feeding over a growing season.
The manure also contributes a wide range of essential micronutrients, such as calcium, magnesium, sulfur, and various trace minerals. Cow manure is an excellent source of organic matter, which improves soil structure, aeration, and water retention capacity. This organic content feeds beneficial soil microorganisms, making it a valuable soil builder beyond its direct nutrient contribution.
Essential Preparation Before Application
Raw, or “hot,” cow manure should never be applied directly to garden beds, as its high ammonia content can burn plant roots. This fresh material must be stabilized through aging or full composting before use. Simple aging involves piling the manure and allowing it to break down naturally for six to twelve months.
Hot composting is a more comprehensive approach, requiring active management to reach internal temperatures of 130°F to 140°F. Maintaining these temperatures kills harmful human pathogens, such as E. coli and Salmonella. This heat also destroys the viability of most weed seeds that pass through the cow’s digestive tract. The final product should be dark, crumbly, and possess an earthy smell, indicating the nitrogen has stabilized and the material is ready for use.
Methods for Applying Manure to Gardens
Once the manure is fully aged or composted, it can be incorporated into the soil using several techniques. The most common method is pre-season incorporation, where a thin layer (half an inch to one inch deep) is spread over the garden surface. This is then lightly worked into the top four to six inches of soil a few weeks before planting.
Side Dressing
Side dressing involves applying a small amount of finished manure around established plants. The material should be kept a few inches away from the plant stems to prevent damage, allowing nutrients to leach into the root zone with each watering.
Fall Application
Applying manure in the fall is also beneficial, as it allows the material to decompose further over winter. This protects the soil from erosion while enriching it for the following spring.
For a liquid nutrient boost, gardeners can create “manure tea” by soaking a porous bag of aged manure in water for a day or two. This liquid fertilizer is diluted and then used to water plants, providing a quick source of soluble nutrients. Different application methods allow tailoring nutrient delivery to the specific needs and growth stage of plants.
Risks and Precautions for Use
Cow manure presents specific risks that require careful management. The primary health concern involves the potential for pathogen contamination, such as E. coli, which can be present in fresh manure. To prevent foodborne illness, raw manure application must adhere to a strict waiting period. For edible crops that touch the soil, such as carrots or lettuce, the manure must be applied at least 120 days before harvest.
A danger comes from persistent herbicides used on the hay or pasture the cattle consumed. Chemicals like aminopyralid can pass through the animal’s digestive system unharmed and remain active in the manure, even after composting. When contaminated manure is used, it can severely injure sensitive broadleaf plants like tomatoes, beans, and peppers, causing twisted growth and stunting.
To mitigate the herbicide risk, it is important to know the source of the manure and the feeding practices of the cattle. Using excessive amounts of manure, even when aged, can lead to an accumulation of mineral salts in the soil, which harms plant growth. Incorporating a modest amount annually, rather than large quantities infrequently, is the safest and most beneficial practice.