Q: I have access to aged horse manure but don’t know how to use it to make a nice flower garden.
A: Aged horse manure is a great source of organic humus for your soil. Humus holds nutrients for plant roots. Since humus particles are tiny, the manure combined with clay can result in poor internal drainage. In your flower beds, mix one inch of manure plus one inch of mini pine bark nuggets plus one inch of gritty sand six inches deep into the existing soil. The mounded bed that results will make a great home for anything you care to plant.
ADDITIONAL NOTE: Make absolutely sure the horse manure comes from a farm where herbicides are not used on the pasture. Weedkillers, particularly Grazon, can linger in manure and harm garden vegetables.