This past month I was at one of the rural schools in our community doing a program on trees. In the end, we checked on a couple of trees in the yard. Students arrive at this school by bicycle or horse-drawn buggy. Consequently, this is a lot of horse manure and they were mulching the trees with ample amounts.In life, we learn that too much of a good thing is not necessarily good.
A great example is too much sugar. A little bit of candy or pop is great tasting. A little more and we are now overweight and our teeth are beginning to deteriorate. I once read about a person that exhumed centuries after their death and could identify them as nobility due to their rotten teeth. They were one of the few that could afford sugar.
Horse manure is a great source of organic matter and fertilizer that can be added to the soil. Horses are fiber consumers but their digestive systems do not allow them to be as efficient digesters as cattle, sheep, and goats. Rather than have a big rumen fermentation vat at the front of the digestive process like in cattle, they do their fiber utilization in another smaller structure called a cecum between the small and large intestines. That hay that passes through a cow is a lot less digested coming out of a horse. It has a lot more form when it hits the ground, hence the term road apples.
Because of all that fiber, there is a lot more decomposition to be done. Placed in any type of pile, the manure will further decompose and part of that process is heat production. That heat can be detrimental to plants it is allowed to touch. If the manure is placed in a pile and allowed to compost for 6 months, a lot of decomposition takes place and it becomes an excellent soil amendment.
The yard tree had an additional problem with the manure, it was touching the bark. That moisture directly against the bark will eventually cause the tree to rot. Bark tissues are different than roots and cannot handle as much moisture. The bark is dead, dry tissue that protects trees from a wide range of challenges such as dehydration, oxidation, and direct access to the living tissue beneath plant pests and pathogens.
Organic mulch may be the most important component in a healthy landscape but if not properly done, it can be detrimental. Some people pile mulch against a tree in a form we call volcano mulching. The damage is irreversible if not recognized and corrected early. It can start changes to a tree’s root system that can remain throughout life.The tree would like for you to spread the mulch out from a few inches to several yards from the trunk.
A tree can use no more than 4 inches of loose mulch. Tree roots need air to survive and too deep of mulch will stop air from getting to the roots. Also, the tree will send roots up into the airy mulch, then if we do not keep the moisture adequate, they will dry out. There is more of an art behind mulching than most people think.
Horse manure mulch fails several tests, but I do enjoy writing a column that compares it to sugar. I think some dentists might agree.