There is more to mulch than meets the eye. Yes, it still prevents weeds, reduces water evaporation from the soil, and keeps roots cool in the summer. However, while mulch does all these good things for plants, I believe the essential role of mulch is to serve as food for earthworms. Earthworms pull particles of organic mulch down into the soil for lunch for themselves and for billions of beneficial soil microbes found in healthy soil.
A good population of earthworms and beneficial soil microbes perform many valuable functions that help plants grow well and stay healthy. The unfortunate truth however, is that few homeowners have anything close to “healthy soil”. I suggest that much of the soil in home landscapes in Metro Detroit is compacted and sadly lacking organic matter. You usually find less than 1% when over 5% is what is found in healthy soil. With little organic matter in the soil, there are few earthworms and soil microbes, simply because there is not enough food for them. A soil that is compacted and deficient in soil critters is essentially dead soil which can’t do much to help plants grow and stay healthy.
Mulch as food is not a new idea. For ten million years, critters in the soil of the forest were fed from the supply of leaves and needles that fell to earth every autumn. Mother Nature knew how to use mulch to feed soil critters.
Then man came along and invented the suburbs. He created lawns and planted trees and shrubs, and worked hard to keep things tidy. He collects grass clippings and rakes up leaves, disposing of them elsewhere. To make matters worse most of us use no organic mulch at all. So by being tidy we have cut off the food supply for the vast and complex soil food web, inadvertently making the care of plants in our yards much more difficult.
Consequently, we have to provide our plants with most of the nutrients they need by fertilizing; key nutrients are not available from a dead soil. We have to water our plants frequently because our soil does not have sufficient organic matter which acts like a sponge to store water. We have to use pesticides to address insect and disease problems; in large part because our landscape plants are in stress from living in dead soil. By ignoring the needs of the inhabitants of the soil we have made a lot of work for ourselves.
Organic Mulch Repairs Bad Soil
The good news is that organic mulch is the best way we have to repair our soil in an existing landscape. Use organic mulch under every tree and shrub, on all the garden beds, and even on the lawn (a topic for another column). Organic mulch is the only consistent way to provide food for the earthworms who in turn serve as the caterers for the rest of the soil folks.
Types Of Organic Mulches
Now for the bad news – there are very few types of mulch available in the marketplace appropriate for feeding soil creatures. Almost all the mulch materials sold today are chunks of bark or wood of various sizes. Worms can’t chew on chunks of wood.
The mulch that does do the job is bark or wood chips that have been shredded in some way, creating some worm sized bites. It decomposes more quickly than the chunks, thus feeding worms all season long. There are a fair number of tree service companies and landscapers in Metro Detroit who recycle wood chips by processing them in a machine called a “tub grinder”. Usually that shredded material is composted for a year, then sold as an outstanding mulch which performs all those valuable mulch functions while at the same time serving as a cafeteria line for earthworms.