Should You Mulch Around Trees? (3 Things To Know)


Putting a mulch ring around a tree makes your landscape look great.  However, mulching around a tree may put its health at risk if you go about it the wrong way.

So, should you mulch around trees?  When used properly, a layer of mulch around a tree will speed up its growth by providing nutrients and organic material.   A layer of mulch also prevents weeds and retains water in the soil below.  When mulching around a tree, use a layer 2 to 4 inches thick, depending on the type of mulch and the type of soil below.

Of course, it is possible to use mulch improperly.  Applying too much or putting it too close to the tree can hurt the roots or damage the trunk at the base.

In this article, we’ll talk about how to mulch around trees properly and what mulch to use.  We’ll also answer some common questions about mulching around trees.

Let’s get started.

Should You Mulch Around Trees?

In general, it is a good idea to mulch around trees.  After all, by mulching around a tree, you are simply imitating what happens in nature.

tree with mulch
Trees get mulch in nature, so why not in your yard?

In a forest, trees are mulched by all kinds of organic matter, including:

  • fallen leaves
  • dead plants
  • rotting wood from branches
compost
Leaves make a good mulch and will decompose to provide nutrients for trees.

All of these materials decompose over time, acting as mulch to help protect trees and help them grow better.  Even though the trees in your yard may not have the benefit of living in a forest, you can still provide them with mulch.

A good layer of organic mulch has several benefits for trees, including:

  • Weed prevention (mulch smothers existing weeds and prevents new ones from growing, which helps young trees to get established without competition).
  • Water retention (by providing shade, mulch keeps soil cool and slows down water evaporation
  • Plant nutrition (as mulch decomposes, it provides available nutrients and organic material).

All trees can benefit from a layer of mulch.  Just remember to use less mulch for younger trees.

According to Texas A&M University, mulch around a young tree can encourage roots to grow into the mulch instead of the soil.  This will lead to shallow roots and restricted growth.

Will Putting Mulch Around A Tree Kill It?

Putting mulch around a tree will only kill it if the mulch is applied improperly.  Improper application of mulch includes:

  • A layer of mulch that is too thick (4 inches is the maximum mulch depth – and even less for clay soil).
  • Mulch that is piled high too close to the tree trunk (also called “volcano mulching”).

Why Keep Mulch Away From Tree Trunks?

According to the University of New Hampshire Extension, putting mulch too close to tree trunks can cause numerous problems.  Mulch keeps a tree trunk wet and makes it more likely that environmental factors will damage the tree, including:

  • Diseases
  • Insects
  • Rodents
tree with canker
Over mulching can damage trees and make them susceptible to canker and other diseases.
Image courtesy of user: RhinoMind via:
Wikimedia Commons: https://commons.
wikimedia.org/wiki/File:
Tree_canker_(beech).JPG

Piling up mulch higher near the tree trunk (known as volcano mulching) is even worse.  This practice can lead to damage further up the tree trunk and prevent the tree from moving energy and nutrients through its tissues.

According to Rutgers, over mulching and volcano mulching can cause numerous problems for trees, including:

  • Suffocation of tree roots (lack of air and oxygen in the soil, which can occur when soil stays too wet).
  • Inner bark death (this can prevent the tree from moving water and nutrients between the roots and leaves).
  • Disease (caused by fungi and bacteria, which thrive in moist conditions caused by too much mulch).
  • Excess heat (due to a combination of summer sun and decomposing mulch).

A canker (or sunken dead area) on a tree trunk is one symptom of over mulching.  Once a tree begins to show signs of damage, it is susceptible to disease and is more likely to decline further.

Does Mulch Around Trees Help Them?

Mulch around trees helps them by preventing weeds, retaining water in soil, and providing plant nutrition.  All of these factors will help trees with mulch to grow faster than trees without.

mulch ring around tree
A ring of mulch around a tree can help with nutrition, water retention, and weed suppression.
Image courtesy of user:
Lamiot via:
Wikimedia Commons: https://commons.wikimedia.
org/wiki/File:
Burghley_House_Park_
landscape_april_2017_29.jpg

In fact, according to the Kansas State University Extension, a mulch ring around a tree can speed up its growth to nearly double that of a tree without mulch!

When Should You Put Mulch Around Trees?

You can add mulch around trees at any time of year.  However, the Penn State University Extension suggests that the best time to mulch around trees is in mid-spring.

You may need to add mulch every year, depending on how fast the mulch decomposes.

Mulches with smaller particles (such as shredded wood) will decompose faster than larger particles (such as large wood chips).  As a result, you will need to replace finer mulches more often.

Some mulches, such as cedar, contain natural oils that help them to resist decay. As a result, they will last longer than other types of mulch.

red cedar mulch
Small mulch particles (such as shredded mulch) will decompose faster than large chunks (such as wood chips).

Add enough mulch each year to maintain the depth of mulch.  As the bottom mulch layers decay and are used by the tree’s roots for growth, you will need to apply more for maintenance.

How Do You Mulch Around A Tree?

To mulch around a tree, it is important to use the proper mulch depth and to keep the mulch away from the tree trunk.

A good rule is to keep the mulch line at least 6 inches from the edge of the tree trunk.  The Penn State University Extension suggests mulching out as far as the tree’s drip line (where the farthest branches reach).

According to the Iowa State University Extension, a layer of mulch around a tree should be 2 to 4 inches deep.  A layer of mulch that is too thick prevents air from getting into the soil below.

wood chip mulch
A layer of mulch for a tree should be 2 to 4 inches deep, depending on soil type.

Mulch that is too deep may also form a layer that water cannot penetrate.  This layer may retain moisture in soil, but water will not be able to get down to the soil easily.

The depth of mulch needed depends on a few things:

  • Mulch type
  • Soil type
  • Tree water needs

A tree that needs lots of water might be able to tolerate thicker mulch, since it will use up water in the soil much faster.

What Is The Best Mulch To Use Around Trees?

The best types of mulch for trees are organic ones, such as:

  • Wood chips
  • Tree bark
  • Pine needles
  • Leaves
  • Compost

The Utah State University Extension recommends against plastic sheet mulch around trees.  Although it will prevent weeds, a plastic sheet will also prevent air and water from getting into the soil.

mulch
Organic mulches (including wood chips) are better for trees than non-organic mulches (such as plastic sheets or rubber).

In fact, they recommend against any non-organic mulch (such as gravel or rubber) around trees.  These mulches will not decompose to provide nutrients and organic material for trees.

Mulch For Sandy Or Clay Soil

The depth of mulch depends on the type of soil you have.  Lighter soil will allow for thicker mulch:

  • For light soil types (such as sandy soil), a thicker layer of mulch is appropriate (3 to 4 inches deep).
  • For heavy soil types (such as clay soil), a thinner layer of mulch is better (2 to 3 inches deep).

The reason to vary the thickness is that sandy soil drains faster than clay soil.

clay soil
Clay soil is heavy and retains water longer than sandy soil. So, use less mulch over clay soil.

A heavy layer of mulch will keep clay soil too wet.  The water cannot drain down through the clay soil quickly and it cannot evaporate past the mulch quickly, so it has nowhere to go.  

You can also vary the mulch depth as you spread it around the tree.  Apply thin mulch near the tree and at the far edges of the mulch ring.

The University of Vermont suggests that mulch can be as thin as 1 inch deep at the point closest to the tree.

Mulching Around Trees Over Grass

If you put down mulch over grass, the shade from the mulch will smother the grass.  You don’t need to dig out the grass itself before applying mulch.

grass
Mulching over grass will smother the grass if the mulch is a few inches thick.

The exception is the area right around the tree itself, where mulch will be little or no mulch.  When pulling up grass, replace any soil you removed when digging (you don’t want exposed roots if you can help it!)

Mulching Around Trees With Exposed Roots

Trees may eventually show exposed roots above the soil surface.  This can happen if the roots come to the surface to get air, or if the roots become thick enough on a large and aged tree.

exposed tree roots
Exposed roots may appear on trees as they age or if the roots cannot get enough air in the soil.
Image courtesy of user:
Lamiot via:
Wikimedia Commons:
https://commons.wikimedia.
org/wiki/File:
Burghley_House_Park_
landscape_april_2017_
Charme_Carpinus.jpg

You can still mulch around trees with exposed roots.  However, you need to pay extra attention to the depth of the mulch.

The Texas A&M Extension suggests putting a maximum of 2 inches of soil or mulch over exposed roots in a single year.  A deeper layer can suffocate roots and damage the tree.

Conclusion

Now you know how to mulch around trees and what types of mulch to use.  You also know what to avoid to keep trees healthy with proper mulching.

You might also be interested in reading my article on salt tolerant trees.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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