Growing Together: Mow over leaves for healthier lawn

Don Kinzler
Forum News Service

Did you hear about the guy who doesn’t believe in repeating gossip, so you need to listen closely the first time? I don’t repeat many of our gardening columns from year to year either, unless it’s with a new twist, new research — or it’s a topic that’s proven popular.

Today’s topic has generated more interest in past years than even tomato blight. The thought of never raking leaves again is welcome news for many lawn owners.

The concept is simple: Lawns become healthier if leaves are mulched back into the lawn with the mower, instead of raking them away.

Surprisingly, mowing over fallen leaves and letting them remain is great for the lawn, and there’s research to prove it. In the late 1990s, Michigan State University wanted a research-based answer to the question of whether it’s better to remove leaves from the lawn or pulverize them back in. During the extensive three-year study, scientists considered three different leaf layer thicknesses: none, 3 inches and 6 inches of mixed tree species, mulched in with a rotary mower every October.

In summary, mowing leaves back into the lawn proved beneficial for turf health. Lawn areas where leaves were mulched were healthier than the lawn area receiving no pulverized leaves. MSU concluded, “Research clearly indicates that mulching leaf litter into existing turf grass provides benefits for the soil and turf grass plants by adding nutrients, retaining soil moisture, loosening compaction and reducing weed growth.”

MSU’s findings have made a great impact on autumn lawn care. Their studies showed that homeowners can achieve a nearly 100% decrease in dandelions and crabgrass by mulching autumn leaves for three years, as the shredded leaves cover up bare, weed-prone spots between grass plants. Mulched leaves keep the turf’s soil warmer in winter and cooler in summer. Mulched lawns green up faster in spring, with less fertilizer needed.

Researchers at MSU suggested using a rotary mower that pulverizes leaves well, such as a mulching mower or a mower with the discharge opening covered, and with the mower height adjusted to a high setting. Leaves should be dry and mowed slowly with a sharp blade to grind leaves fine. If leaves are still in large pieces, go over the lawn again at right angles to the first pass.

The optimum time to mulch the leaves is when you can still see some green grass through the fallen leaves, rather than letting the leaves gather too thickly.

Pulverized leaves should settle into the turf within a few days, and remaining leaf litter shouldn’t be allowed to cover grass blades entirely. If leaves accumulate in a layer too thick to mulch, an option is to rotate by raking or bagging one week, then mulching the next.

The beneficial effects of mulching leaves back into the lawn are most noticeable after following the practice for several years. Leaves are a natural soil-builder as they decompose. Besides MSU, mulching leaves is advocated by Purdue University, the University of Minnesota, North Dakota State University, Consumer Reports and even Bob Vila.

The Scotts Co., well-known for its lawn products, also advocates the process. “Take the grass catcher off your mower and mow over the leaves on your lawn. You want to reduce your leaf clutter to dime-size pieces. You’ll know you’re done mowing leaves when about half an inch of grass can be seen through the mulched leaf layer. Once the leaf bits settle in, microbes and worms get to work recycling them. When spring arrives, the leaf litter you mulched up in the fall will have disappeared.”

Don’t let unmulched leaves lay on the lawn over winter, as they can smother grass. If your yard has too many leaves to mulch into the lawn, you can put the bagger attachment on, collect the leaves and spread the mulch on flower beds and gardens, incorporating it into the soil. Microorganisms will break down the organic materials, improve soil health and release nutrients. Mulched leaves will biodegrade and disappear by spring.

Well, there you have it. Raking leaves may soon be relegated to nostalgia and Normal Rockwell prints. I will admit, though, I miss the autumn aroma of a burning leaf pile.

Fielding questions

Question: Attached are photos of our huge maple tree in the backyard. While mowing, I noticed piles of nuts gathered at the base of the tree. Then I realized they were embedded throughout the bark of the tree and in the notches of the branches. I’ve never seen this before and we have lived here since 1995. I did some research and think they are butternut nuts. Have you heard or seen this before? — Berta S.

Answer: From the shape, I think you’re correct about them being from a butternut tree, whose botanical name is Juglans cinerea. Butternut is more borderline in winter hardiness than its close cousin the black walnut, which is Juglans nigra. Black walnut fruit are more rounded and butternut fruit are more lemon-shaped, which the fruit in the photo seem to be. Inside these fruits are the walnutlike nuts.

It’s fairly common for squirrels to gather black walnut seeds and “squirrel them away” in odd places, such as people’s flower planters, flower beds and gardens, where they sprout the following spring. I’ve seen the fruits piled in little crevices at the base of trees, but I don’t think I’ve ever seen them embedded in the bark the way your photo shows.

The presence of these fruits in your maple tree shows that there must be a mature butternut tree somewhere close by.

Q: I found a squash that’s light green, the size of a pumpkin, and it’s the only one like it in the squash patch. All the rest are the normal buttercup squash. I’m wondering what would cause this? — Harold P.

A: The lone squash of a different type that you found in the buttercup patch is most likely the result of a seed in the original seed packet that was of that type. Occasionally seed mix-ups happen in packaging seeds, which is understandable when seed types look nearly identical, as with various types of squash.

One easy explanation of mix-ups is in the equipment used to package seeds. When one batch of squash seed is run through the machinery and the machine is cleaned before switching to another type of squash, one seed clinging in a crevice can easily end up in the packet of the next type.

It might mistakenly be thought that this was the result of some type of cross-pollination in your garden. That wouldn’t be the case, because any type of cross-pollination in your buttercup squash affects the seeds inside the fruit, not the appearance or size of the fruit itself. It will be interesting for you to sample the squash.

Q: I have a Haralred apple tree and the apples are big and so nice but very sour. Next door there’s a flowering crab tree, and I’m wondering if it pollinated with my Haralred apple tree, making the apples sour. Is that possible? I’m not sure what to do with the apples. I’m going to wait for a hard freeze to see if they will sweeten. — Betty S.

A: Haralred apples don’t ripen fully until well into October, so they should be left on the tree as long as possible, as cooler temperatures promote the conversion of starches into sugars. Haralred is a redder-skinned version of Haralson, and both can be quite tart if sampled in September. By now, we’ve had more frosts, and hopefully the apples have begun to taste less tart.

There’s no need to worry about cross-pollination affecting the fruit. Apple trees actually require cross-pollination from a variety different than itself to produce fruit. Flowering crabs are great sources of pollen, as bees fly among trees. The pollen affects only the seeds inside the fruit, not the fruit itself or its quality. That’s why if you plant a seed from inside one of your Haralred apples, the resulting seedling will be different, depending on where the pollen came from.

Research has shown that mulching leaves back into the lawn makes healthier turf as opposed to raking leaves away.
A reader was surprised to find nuts embedded throughout the bark of their maple tree.