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Stop building 'mulch volcanoes.' How to mulch properly to stop killing your trees and plants.

Spring planting season has arrived and, again, a record number of Americans are readying for the annual rite of spreading mulch throughout their planting areas and trees.

More than 80% of U.S. households took part in lawn and garden activities in 2022, according to the 2023 National Gardening survey, due out later this month. That means the number of U.S. homes with gardeners has grown to more than 105.1 million, according to the National Gardening Association, which surveyed 2,601 Americans between Jan. 9-Feb. 2, 2023.

Last year, the number of U.S. households gardening passed 100 million for the first time, the association said. That growth came in part because of the COVID-19 pandemic, NGA executive director Dave Whitinger told USA TODAY.

Now, inflation is having an effect on gardening trends. "Our survey found that people are decreasing their ornamental gardening in favor of food gardening," he said.

More homes (21%) expected to increase spending on food gardening, while 26% planned to decrease spending on flower gardening, the survey found.

So more of us are growing things. Is it time to plant?

Spring arrival: Early in Southeast, late in the Southwest and central U.S.

Measured by the arrival of the first spring leaves and blooms, spring is arriving earlier than usual in much of the U.S.

Parts of the Southeast, lower Midwest, mid-Atlantic and New York City are seeing the earliest spring leaf on record, or a spring that occurs once every 40 years, according to The National Phenology Network.

However, spring is arriving later than normal in parts of Colorado, Kansas and Missouri, as well as California and Arizona in the West.

You can track the status of spring viewing the maps on the network's website.

Before you start planting make sure the soil temperature is warm enough – 50 degrees Fahrenheit for cool crops such as peas, leafy greens, parsley, and 60 degrees or higher +F for warm season crops like peppers, tomatoes, and basil, said Brooke Edmunds, a community horticulturist with the Oregon State University Extension Service.

And make sure to watch for late spring frosts, which could damage your plants, she said.

But where does mulch come in? And how do you know you are mulching right and you aren't actually harming – or potentially killing – your plants and trees?

Let's look into the basics of mulch.

What is mulch?

Most popular mulches are bark and wood chips. But other organic substances such as compost, pine straw and ground-up bark or leaves are also placed around flowers, plants and trees.

Organic mulch is "great for every type of gardening, though we recommend different materials depending on the application," said Cheryl Boyer, a professor in the department of horticulture and natural resources at Kansas State University in Manhattan, Kansas.

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Shredded bark mulches are what you likely think of when you think of mulch. They are typically made of pine or hardwood tree bark. Some may be called bark nuggets.

What type of mulch is available and recommended where you live can be different as "local availability of mulch often determines what material is used in different parts of the country," she said.

Use mulch to cover up any bare soil spots to keep weeds at bay.
Use mulch to cover up any bare soil spots to keep weeds at bay.

What does mulch do?

Organic mulch protects and fosters plants and trees by maintaining soil moisture, repelling weeds and improving soil quality.

Mulch also keeps the soil around plants and trees warm, helps promote early spring growth of plants and root growth for trees and hinders soil erosion.

Wood chips and bark chips placed around flowers and trees keep "moisture from evaporating from the soil after watering or it rains," Edmunds said. "Mulch can also keep weed seeds from germinating and makes it much easier to pull out the weeds that do."

Whatever the size of your tree, "all trees can benefit from mulching," she said. "Competition for water from grasses and other ground covers can be eliminated by adding a layer of mulch around trees."

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Pine bark mulch in a flower bed after planting in spring.
Pine bark mulch in a flower bed after planting in spring.

That layer also beautifies your yard or garden and protects trees and plants from other dangers. "A ring of mulch allows you to bring your lawnmower right up to the edge of the mulch, eliminating the need for string weeders," said Virginia Cooperative Extension horticulture agent Adria Bordas. "At the same time, you are protecting tree trunks and surface roots from damage by mowing and clipping equipment."

Stop building 'mulch volcanoes.' You're killing your trees

OK, we now know the benefits of mulch. But you can use too much. When it comes to trees, try to avoid the dreaded "mulch volcano," a volcano-shaped mound surrounding the base of your tree.

Mulch piled up in a 1- or 2-foot tall mound "around the trunks of young trees is taking a good idea way, way too far," said Paul Cappiello, executive director at Yew Dell Botanical Gardens in Crestwood, Kentucky. "Aside from being bad for your trees, it costs you money – either just materials (if you’re doing the volcano building yourself) or materials and labor (if you hire it out)."

The problem? "When the mulch is mounded around trees it will hold that moisture up against the trunk. This can promote decay and rot of the tree," Edmunds said.

Building a mulch volcano of even more than 3 inches deep is "somewhat like wearing a turtleneck in the summer," Boyer said. "Trees with too much mulch around the base of the trunk experience a wide variety of stress."

This can especially hurt newer trees, which may be planted too low, by covering up the tree's root flare and smothering its ability to exchange oxygen and thrive. Too much mulch can also attract pests and diseases.

Research done at K-State found newly planted trees can grow up to 300% more in the first two years of growth if the grass around a tree is removed, Boyer said. Mulch is used after grass removal to protect that area around the tree.

When spreading mulch around your tree, envision a doughnut. Spread mulch about 3 inches deep, preferably to the tree's dip line. But around the base of the tree, pull mulch back so it avoids contact with the trunk. "The soil will stay moist but the trunk won’t," Edmunds said.

You can add a thin layer of compost topped with mulch to improves the habitat for beneficial soil microbes such as bacteria and fungi, she said.

It's not just trees that can suffer from mulch volcanoes. So can shrubs. "You can suffocate the roots of shallow-rooted species and cause cankers to develop around the bases of susceptible trees and shrubs," Bordas said.

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Contributing: Louisville Courier Journal

Follow Mike Snider on Twitter: @mikesnider.

This article originally appeared on USA TODAY: How to mulch: You can use it around trees, plants without killing them