What to do when your lawn is covered in fallen leaves – San Antonio Express-News

what-to-do-when-your-lawn-is-covered-in-fallen-leaves-–-san-antonio-express-news

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This time of year in San Antonio, much of the lawn’s care is devoted to dealing with leaves dropping from trees. There are many questions I am often asked about how to handle the leaf drop. Here’s a sampling.Q: How can trees that are the same species and even in the same landscape have such a different pattern of dropping their leaves?
A: The main reason is that each tree is genetically different from the trees of their same species. Almost all shade trees are produced from seed, which means their origin was based on a mix of different parent genetics. With seed-produced trees, the genetic makeup governing leaf drop can be quite different, and that difference can be expressed in the speed of leaf drop and other characteristics.

That reproduction method is very different from shrubs or small trees that are reproduced vegetatively, so genetics are identical from plant to plant.

Genetic differences can explain much of the difference in leaf drop by the same species of tree in the same landscape, but there are other factors. Microclimates can have a huge impact. It is amazing how much of difference there can be in wind patterns, soil depth, soil fertility, soil moisture, sunlight access and temperatures within just a few feet. All of issues can affect various trees’ leaf drop.

For years, gardening experts have encouraged raking up and disposing of the leaves on the lawn. No longer. It’s not so much that they should always be left where they fall, but that if you do rake them up, you utilize them.Campwillowlake /Getty Images / iStockphoto

Q: How can it be true that leaving the leaves on the lawn to decompose is not a problem?

A: For years, gardening experts have encouraged raking up and disposing of the leaves on the lawn. No longer.

It’s not so much that they should always be left where they fall but that if you do rake them up, you utilize them. The leaves can be used as organic material for the lawn, as mulch in the shrub border or for organic material for the compost pile.

Leaves’ organic material is too valuable to be discarded in the landfill. Such a fate is a double waste: You lose access to the nitrogen and other nutrients in the leaves, and the valuable organic material takes up valuable space in the landfill.

Some gardeners will say that the amount of nutrients in dropped leaves is minuscule and even recommend enriching the addition of the leaves to the compost pile with a dose of lawn fertilizer or lush green materials. That is true. But even the small amount of nutrients in brown leaves is a valuable as an additive to the lawn’s soil.

For years, gardening experts have encouraged raking up and disposing of the leaves on the lawn. No longer. It’s not so much that they should always be left where they fall, but that if you do rake them up, you utilize them.canghai76 /Getty Images / iStockphoto

Q: What if the leaf covering on the lawn is so thick they decompose too slowly? Won’t that suffocate some of the lawn grass?

 Protect your primula, pansies, calendulas and other low-growing flowers from slugs and snails by applying a slug and snail bait. Follow label instructions.
 Grassy weeds such as rescue grass and annual bluegrass are growing in shady lawns. They can be controlled with a contact herbicide such as Grass-B-Gon or Poast if the lawn grass is dormant. But a better option may be to treat the grass as a sustainable winter lawn and keep it controlled with weekly mowing.
 When temperatures are at or below 40 degrees, move your bougainvillea, oriental hibiscus, mandevilla and other tropical plants into cold protection shelter.
 Harvest up to one-third of the foliage from spinach, kale and chard every three weeks to maintain the plants' productivity and provide greens for the table. It is also important to keep the plants fertilized.

A: I suppose some places with deep rich soil and/or freezing temperatures might end up with a leaf covering so deep that it interferes with the lawn performance, but that is not the case in the San Antonio area.

In my experience, the leaf cover is not very deep, and the leaves of common trees here (oak, cedar elm, pecan, sycamore and others) generally decompose in four or five weeks. To speed up the process, it works well to run the lawn mower over the leaves.

Q: Most of the leaf drop is by oak and pecan trees. Why isn’t the tannic chemistry of the leaves a problem here like it used to be out East?

A: We scientists may have overestimated those leaves’ negative chemistry out East. But even if we didn’t, the tannic acids and other chemicals in some of those leaves are really not a negative factor in our situation because our soil is mostly a highly buffered alkaline mix that quickly overcomes any available acidity.

Calvin Finch is a retired Texas A&M horticulturist. [email protected]

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