Readily available in many rural areas and very often offered free of charge , horse manure makes a suitable and inexpensive fertilizer for plants.
Fresh manure should not be used on plants to prevent the possibility of burning their roots. However, well-aged manure, or that which has been allowed to dry over winter, can be worked into the soil without the worry of burning.
While it may be nutritional, horse manure may also contain weed seeds. For this reason, it is usually better to use composted horse manure in the garden. The heat produced from composting can effectively kill most of these seeds as well as any harmful bacteria that may be present.