In the Garden:
Apple scab disfigures the foliage and reduces flowering and fruiting on apple and crab apple trees. (Photo by Kate Jerome)
How Raking Can Save Your State Budget
When I was growing up in New Jersey, Saturday mornings were leaf-raking-and-burning time. In my neighborhood and in many others across town, the acrid smell of burning leaves filled the air. The smoke tickled the nostrils and burned the eyes. Someone finally figured out that leaf burning wasn't healthy, and nowadays it's banned in many parts of the country. But aside from the downside of burning the leaves, is all that raking really necessary? Why not let the leaves fall where they may and break down into nutritious mulch for our gardens? Are Saturday morning rake-a-thons just a symptom of our preoccupation with lawns? What harm do all those leaves cause anyway?
While burning the leaves has the potential to make us sick, letting leaves lie where they fall has the potential (I stress the word "potential") to make our plants sick. It all depends on the health of your trees and shrubs.
Scabby Crab Apples
Consider my crab apple tree. A few years ago I noticed that there were very few flowers on the tree in spring. Then in summer, dead leaves kept falling. The branch tips had turned brown, and many leaves still on the tree had brown spots. There were very few of the beautiful orange fruits -- one of the main reasons I had chosen that tree. Clearly apple scab was the culprit, a fungal disease that afflicts many crab apples, apparently even my variety, 'Harvest Gold', which was touted as resistant.
Because the tree is in the middle of a mixed border, raking is tricky, and I had been letting the fallen leaves decompose in place and form a nice layer of mulch. After all, leaves decompose into a thick, humusy layer in the forest and why shouldn't we take advantage of that in our gardens? The problem is that fungal diseases can overwinter in fallen leaves, as well as in fruits and other plant parts. In spring the fungal spores are spread by splashing water or wind to the newly opening buds, so the new foliage and flowers are infected as soon as they begin to grow.
Inadvertently, I had been making it easy for the disease to merrily develop and spread by not raking up the infected leaves.
An Ounce of Prevention
Plant pathologists call the prerequisites for disease a "disease triangle" -- host plant plus disease organism plus an environment conducive to the spread of the disease. Many fungal diseases depend on weather that makes it easy for them to spread: namely wet weather. While I can't control the weather, I can try to make the environment around my crab apple less hospitable to the scab by thinning the branch canopy to allow more sunlight and air flow around branches. (I'm now ruthless about this every spring.) I also can reduce the disease that lies latent in those leaves that blanket the ground by raking them up and disposing of them as far away from other apple and crab apple trees as possible. A hot compost pile might kill the spores but it's chancy. Burning would kill the spores but ... oh well.
My rose bushes with black spot take an extra measure of precaution. Some don't drop all their leaves in the fall, and black spot spores can overwinter in foliage on the plant and in rose canes. So I don my rose gloves and pull off any leaves still hanging on in late fall and drop them into a bucket. Then prune off any dead canes, rake the ground and dispose of all the debris.
As for our lawns, if fallen leaves -- even disease-free leaves -- are left on top of the grass, they can compact, reduce sun and air to the grass plants, and encourage disease.
Bottom line: Fall raking is largely about disease prevention.
Ok, it's also about grooming our yards, about showing our best face to the world. Even if you don't care if your trees have some diseased foliage, at least think of how this could tarnish the image of your neighborhood, even of your state. The Hartford Courant newspaper in Connecticut reported recently that the diminished color of Connecticut sugar maples this fall is due to an unusual fungal disease that caused leaves to turn brown and fall off before showing the vibrant colors that draw flocks of people to New England in autumn. Tourist dollars are at stake. Go outside and rake!
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