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Save your back this fall -- mulch your leaves

Bob Dluzen
Special to The Detroit News

Fall leaf colors are near peak condition in southern Michigan. That means leaves will be falling faster with each passing day prompting homeowners to dig out their leaf rakes.

Many people view leaves as a litter problem to be removed and disposed of, not much different than random trash blown into their yard. But leaves are much more than that.

Leaves are the direct result of months of sunshine along with tons of carbon dioxide coming together through photosynthesis.

During the growing season, a tree must extract vital minerals from the soil to build its life support systems. Those minerals are the same that all plants require.

The list of macronutrients include nitrogen, phosphorus, potassium, sulfur and calcium. Several other minerals that are required in much smaller amounts are known as micronutrients.

Many of these minerals taken up by the tree are used in the leaves and stored there. It’s a shame to waste all of that leaf energy by gathering them up and throwing them away.

In a forest nothing is wasted. Fallen leaves become food for future growth and new generations of trees. As years go by, the forest floor soil becomes rich with nutrients provided by decomposing leaves. There are ways to mimic that same process in your yard.

Contrary to a common myth, even oak leaves will not make the soil “sour”. They will increase soil fertility but have no effect on soil pH.

One alternative to bagging leaves and setting them out on the curb is to build your own compost pile. But that would mean a lot of raking would need to be done. 

Just letting the leaves lie on the grass all winter is not a healthy thing to do to your lawn. Those fluffy leaves will soon flatten down and form an impervious mat that can smother grass.

Chopping leaves into small pieces is the game changer. Running over fallen leaves with a lawn mower is the simplest and easiest way to deal with autumn leaves. Sometimes you'll hear this called mulching leaves. No special mower or blade is needed.

There are just a few simple guidelines you need to follow for it to be successful. First, raise your mower blade height to its highest setting. You want your grass to be tall enough so it doesn't  get completely covered during the process.

Then simply mow the leaves first in one direction, then crossways to the first mowing.

The idea is to chop as many of the leaves you can into pieces about the size of your thumb nail. Depending on the depth and texture of your leaves you may have to make several passes to get the desired results. If the leaves are freshly fallen and dry, a fair amount of the material will be reduced to dust sized particles.

Proper mulching technique will reduce leaf volume down to one-tenth of what you started with.

Some turf grass researchers suggest mulching several times during the season instead of waiting for all of the leaves to fall off the trees. Others say you can chop up to one and a half feet all at once without causing problems. That would depend on the species of tree. Hard, tough cottonwood leaves are more difficult to process than more tender maple leaves for example.

It’s critical to make sure there are grass blades sticking up through the mulched leaves when you’re done. You do not want the grass completely buried.

Mulched leaves have a high carbon to nitrogen ratio that will cause a jump in the soil fungus and bacteria population. This in turn causes a temporary loss in available nitrogen for the grass. If you have a high maintenance variety of grass, you may want to do a fall fertilization to offset the effects of low nitrogen.

Mulching leaves is not a replacement for regular lawn fertilization. However, if done consistently, it will add to the fertility of the soil. So think of mulching leaves as more of a labor-saving venture.

With practice, you’ll be able to come up with a leaf mulching system that allows you to mulch your leaves while still maintaining a nice appearance to your lawn.