Farm Horizons, October 2014

You don’t have to rake all those leaves

By Christine Schlueter
McLeod CountyMaster Gardener

Is it necessary to rake the lawn? The real answer to this question is, “no,” but it comes with one catch; the most important point with fall cleanup is that the tree leaves are not covering a significant portion of the turfgrass canopy. About 10 to 20 percent coverage of your lawn might be OK, but make sure the leaves aren’t covering any more than that.

Based upon research at several universities, the organic matter and nutrients from leaves mown into lawn areas has been proven to improve turf quality.

At Michigan State, researchers set a rotary mower to cut at a height of 3 inches, and then mowed an 18-inch-deep layer of leaves into test plots. That’s the equivalent of 450 pounds of leaves per 1,000 square feet. The tests resulted in improved soil and healthy lawns with few remnant leaves visible the following spring.

Excessive leaf matter on your lawn going into winter is bad for several reasons.

First, it will smother the grass, and if not removed very soon in the spring, it will inhibit growth.

Second, it can promote the snow mold diseases.

And finally, turf damage from critters (voles, mice) can be more extensive in the spring.

The homeowner basically has three options to make sure that leaves are not covering a significant portion of their lawn:

1) Rake them up or use a blower, and compost the leaves or dispose of them.

2) Use the bagging attachment for your mower and compost the leaf/grass mix or dispose of it.

3) Mulch the leaves with a mower (i.e. chop them into small pieces so they will fall into the canopy). This is really the preferred option, because the nutrients and organic matter will benefit the lawn and soil.

Some leaf types have been shown to reduce weed seed germination when mulched into a lawn canopy (maples, others). The leaves of some particular tree species (legumes like honey locust and others) might actually add a significant amount of nitrogen to lawns, because these species fix nitrogen from the atmosphere just like soybeans, so higher leaf nitrogen contents in these leaves is possible.

Successfully mulching leaves into a lawn canopy requires more frequent mowing in the fall and possibly several passes with the mower to mulch the leaves sufficiently.

Specialized mulching mowers can also be purchased, and these mower types will also be beneficial year-round to mulch grass leaves into the canopy. Chopping leaves into small pieces is important.

Under trees or in other shady spots where a lawn won’t grow, you can create planting beds from fallen leaves as a source of soil-building organic matter. Shredded leaves applied as mulch protect tree roots from heat and cold and retain soil moisture during dry spells.

To treat leaves as trash is not the best for the environment. Currently, many municipalities encourage residents to rake leaves to the curb for collection, but before they are collected, heavy rains often wash the leaves into catch basins. There, they decompose and release phosphorus and nitrogen into streams and rivers that flow through the community. These excess nutrients contribute to algae blooms during the summer, which result in lower oxygen levels, making it difficult for fish and other aquatic species to survive.

Municipalities, both large and small, spend thousands, even millions of dollars each year to collect, transport, and process autumn leaves, tying up resources that could be used elsewhere in our communities. If we all keep our leaves on our properties, we will improve our gardens, save money, and enhance the environment we all share

When spring arrives, you’ll notice something. The leaf litter you mulched up in the fall will have disappeared. Your rake will look dusty and neglected. And your grass will look greener than ever.

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