By admin at Oct. 27. 2011.

      It’s that time of the year when the leaves are cascading from the trees. After you have raked three, four or five times do you wonder why you are bothering? After all Mother Nature put them there and doesn’t mother always know best?

      There are actually a number of reasons why raking is recommended if you want to keep a healthy lawn. The first reason is the result of the type of grass that we plant in Pennsylvania. Lawn grasses for zone 5 are what are called cool season grasses. These include fescues, bluegrasses and perennial rye grasses. Cool season grasses do most of their growing during the spring and the fall. They need that fall growth period to build up their root system for winter dormancy. This is particularly important if the summer has been hot and dry. A layer of leaves over the grass during this important growth period will shade the plants and inhibit growth. The grass will then go into winter in a weakened condition.

      Secondly, certain leaves decompose slowly and  can form dense mats especially during wet weather. If you have oak and beech trees the leaves stay intact for a very long time. Waxy leaves such as those from roses, hollies, pines or rhododendrons are also slow to break down. Maple, ash and birch leaves decompose quickly and will probably be gone by spring.

      If leaves mat on your lawn they will do exactly what heavy mulch will do when put over a weed or other plant. The grass, deprived of sunlight, will die. In the spring there will be patches of dead grass and bare lawn.

      Matted and wet leaves also provide an ideal medium for the growth of bacteria and fungi. We cheerfully toss them in the compost bin and expect them to breakdown under the influence of these organisms. The same thing happens on the lawn; they provide a wet, warm environment. While some of the organisms are “good bacteria” and do not affect the grass,   some of them are not so benign.

      One of the chief culprits associated with leaves is snow mold. These molds are active just above freezing temperatures under moist conditions and multiply rapidly under dead leaves and snow cover.  There are a number of different types of snow mold. The pink variety (Microdochium nivale) has white mycelium that ages to pink. Gray snow molds (Typhula spp.) are white or gray. These will be visible in patches of dead grass just as the snow begins to melt. They disappear quickly as the grass dries, so it may be impossible to diagnose just what killed the grass.

      If raking is too time consuming a process an alternative is to mow the leaves. This should be done when they are dry and crisp. Running the mower over them repeatedly will shred them so that they will not mat. As they decay they will put nutrients back into the soil. If all of your trees are oaks or pines they will tend to acidify the soil so adding a bit of lime might be advisable. While helpful to the lawn this process deprives the gardener of the basis of a wonderful and useful compost heap.

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