Perhaps one of the oldest ingredients in compost is manure. Clay tablets made a thousand years before the birth of Moses bear record that the ancient Akkadians mixed camel dung with mud to make a nutrient-rich soil for plants. In today's greenhouse, manure may be mixed with loam to form potting soil or composted directly in the greenhouse to warm plants. Using manure in a greenhouse, however, has its drawbacks.
A greenhouse is a closed environment, and once a disease, virus or insect makes its way into the greenhouse it can rapidly get out of hand. Evaluate all substances brought into a greenhouse for their potential to carry insects, diseases or viruses. Since manure is an animal waste, it must be carefully managed in this environment to avoid contaminating vegetables with diseases that an animal may have been carrying, such as avian influenza.
Manure used in the greenhouse for potting soil must be aged at least six months. Typically, manure that is packed into a pile and left to age will heat to the point that it kills many of the bacteria present. Fresh manure not only contains bacteria, it also contains high concentrates of nutrients such as nitrogen. The nitrogen in manure is so concentrated that if fresh manure were mixed with loam for potting soil, the resulting soil would severely burn plants that were planted in the soil.
Some manures must be avoided for greenhouse use because they have the highest potential for spreading diseases to humans. These manures are cat, dog, pig and human manures. Some diseases, such as swine flu, first developed in pigs and spread to humans thanks to close proximity contamination. Effective manures for the greenhouse include cow, chicken and sheep.
Forage animals such as cattle and sheep often eat weeds that have seed within them. The spread of seed through animal feces is one method that plants use to propagate. If you use manure in potting soil or by composting in the greenhouse, you may inadvertently spread weeds into the greenhouse. Composting manure for six months will help you to evaluate the manure for the presence of weed seeds.
Composting manure also creates methane, which is a volatile gas. Although plants can use carbon dioxide, which is another greenhouse gas, they exude methane as a way of getting rid of it. The presence of additional methane in your greenhouse from composting manure can be detrimental to plants.