mulch wheelbarrow

When used correctly, mulch can provide many benefits to young trees and gardens. It not only prevents weeds from sprouting, it also retains moisture, prevents soil erosion, and regulates soil temperature.

What is Mulch?

“Mulch” is just a fancy word used to refer to any sort of loose material that’s spread over the soil’s surface. It doesn’t matter what the material is – if it’s used to cover the ground, it can be called “mulch.”

There are two general types of mulch – organic (made from living, or formerly living, material) and inorganic (made from non-living material).

Which Type of Mulch is Best?

strawberries growing in straw

A strawberry plant grows amongst straw used as mulch

Both organic and inorganic mulch have pros and cons. Which one is best for you depends on your preferences and yard.

Organic Mulch

Organic mulch is typically made from a wide variety of materials, such as shredded bark, wood chips, compost, cocoa hulls, leaves, pine straw, seaweed, or grass clippings. As it decomposes, it provides nutrients to the soil and improves soil structure, improving the health of nearby trees and plants.

Shredded or chipped bark or wood has a nice, decorative look and are great for trees, shrubs, and gardens where you won’t be doing a lot of digging. Compost can be used anywhere, while straw and hay are best used in a vegetable garden. Shredded leaves or leaf mold also work well as mulch in almost any situation, but if you don’t like the look of them try spreading a layer over your garden beds in the fall so the leaves can begin to decompose over the winter months.

Lawn clippings can also be used as a ground cover, but only if they haven’t been treated with weed killers, herbicides, and pesticides, as these will kill or harm your plants and trees (and you definitely don’t want chemicals in your vegetable garden!).

Be careful where you purchase organic mulch; some may contain noxious weed seeds that will make the job of keeping your yard weed-free a whole lot more difficult, while others can contain pesticides, industrial waste, or other toxic substances.

Inorganic Mulch

Sometimes, inorganic materials like gravel or shredded rubber are used as mulch. They don’t add any nutrients to the soil and are very hard to remove because they don’t decompose like organic materials do. That does, however, mean that inorganic mulches need to be replaced less often than organic ones.

If you choose to use gravel as a ground cover, be sure to keep it away from your lawn; it could hurt your lawn mower and ruin the blade(s).

How Much Mulch Should I Use?

wood chips covering the ground

Trees and shrubs do well with about 2 to 4 total inches of mulch (old mulch plus any new mulch added on top). If you know that your soil doesn’t drain well, stick with just 2 inches.

If you’re worried that 2 to 4 inches won’t last all year, apply mulch twice a year (this is actually the recommended approach).

If you have previously applied several layers of mulch, you may want to remove it before applying more to ensure that moisture can penetrate the layer(s) and surrounding plants aren’t suffocated. This also helps to keep your garden bed looking neat and fresh.

However, because several kinds of mulch decompose naturally, this step may be unnecessary. Just rake it up a bit to let water through and to see how much mulch is left so you don’t put too much on top of it.

We don’t recommend the use of plastic or landscape fabric under organic mulch, as it usually leads to more water runoff and can prevent water and nutrients from reaching plant or tree roots. Plus, it’s not that effective; weed roots grow through the fabric and, when removed, tear it. It also looks pretty bad when the plastic or fabric shows through.

Where Do I Apply the Mulch?

This is one of the most important questions, especially when it comes to your trees. Ideally, mulch should be spread out to the edge of the tree’s canopy (as far as the branches and leaves reach). If that’s not feasible, aim for as large a diameter as possible.

When applying mulch, you want to be able to see the point where the tree trunk flares out into the ground. Make sure mulch is pulled well away from the trunk (it shouldn’t be touching). And the mulch should be flat, not piled up at any point.

For gardens, ensure that the mulch is pulled back at least an inch from plants, shrubs, flowers, and vegetables; mulch should never touch the plants.

Just Say No To Mulch Volcanoes: Mulch Piles Kill Trees

mulch volcano piled around a tree

This is a perfect example of what is referred to as a “mulch volcano,” where the mulch is piled up against the tree. Don’t do this.

It’s vital that the mulch does not in any way touch tree trunks. We know this surprises a lot of people as you’ve probably trees in parks and neighborhoods with mulch piled high around them. We can’t emphasize how bad this is for trees, however.

Known as mulch volcanoes, piling mulch directly around a tree trunk causes many issues, most unseen because the damage is occurring under the mulch. But despite what you can or cannot see, mulch volcanoes have harmed and even killed countless trees.

Because mulch is used to retain moisture when it’s too close to the trunk it can cause fungus and pathogens to flourish, which then attack the tree and cause it to rot.

The moist environment also encourages the tree to put out new roots into the mulch itself. When the roots reach the end of the mulch, they turn back and grow towards the tree, wrapping around it. The tree becomes unstable from these girdled roots, the main roots die, and the tree is unable to get moisture from the ground.

If the ground was already wet when mulch was applied around a tree, the pile of mulch will cause the tree to receive too much water and not enough oxygen. Believe it or not, this actually causes a tree to drown.

Mulch heats up as it decomposes, reaching temperatures around and above 100 degrees Fahrenheit. When piled against a tree, this heat can kill the inner bark in young trees.

Rodents and pests LOVE mulch piles (they don’t love mulch when it’s spread correctly, just when it’s piled up). They burrow into the mulch, happy as can be, and eat the bark of the tree in the center of the mulch volcano. The rodents may be happy, but this is a sure death warrant for the tree.

Finally, over time the mulch against a tree will compact. Water is not able to seep through and is instead repelled. The ground underneath dries out and the tree is left without the moisture it needs.

If you have a tree that has had mulch touching the trunk for any length of time, remove it immediately. If you spot signs of rotting, animal damage, strange root growth above ground or anything else out of the ordinary, contact us to see if your tree can be saved. In some cases, it can, but in others, the tree is too damaged or is unstable and must be removed for safety reasons.

In Summary

If you apply mulch properly, it does a lot of good for your plants and the look of your yard. Just remember to apply a thin, even layer and to keep it away from tree trunks!