How to contain mulch around a tree


Mulching Landscape Trees

Mulches can also improve soil structure and fertility. This is important in urban landscapes where soils are often compacted and lack organic matter, especially on new construction sites.

Mulching mimics the natural environment found in forests where leaves and branches blanket the soil surface, replenishing nutrients as they decompose and creating an ideal environment for root growth. Urban landscape trees and shrubs typically grow in much harsher environments with soils modified by human activities (e.g., construction, lawns, and compaction). A 2- to 4-inch layer of mulch can re-create aspects of a forest's soil environment. According to the International Society of Arboriculture, mulching, when done correctly, is one of the most beneficial practices a homeowner can do for the health of a tree or shrub.

Mulches are available in two major forms, organic and inorganic. Tree care professionals prefer organic mulches, such as wood chips, pine needles, hardwood and softwood bark, cocoa hulls, leaves, and compost mixes, since they decompose, improving soil structure and increasing soil fertility. The various organic mulches decompose at different rates and require periodic reapplication. Inorganic mulches, such as gravel, stone chips, river rock, and rubber, do not provide the same benefits as organic mulches as they do not decompose.

The benefits of proper mulching include the following:

  • Conserves soil moisture by increasing water infiltration and slowing evaporation
  • Improves soil structure, fertility, and aeration as it decomposes
  • Moderates soil temperature, protecting roots from extreme summer and winter temperatures
  • Eliminates potential tree damage from mowers and trimmers
  • Prevents soil compaction by reducing foot and vehicle traffic, allowing roots to “breathe"
  • Impedes growth of weeds and grass that compete with tree roots for water and nutrients

Inorganic mulches, such as this stone, do not provide the same benefits as organic mulches like bark and wood chips

The benefits of mulching are well documented. However, excessive or improperly applied mulch can adversely affect plants. The International Society of Arboriculture advises to apply mulch properly; if it is too deep, piled against the trunk of the tree, or the wrong material, it can cause significant harm to trees.

Proper Mulching Method

  • Organic mulches are preferable due to their soil-enhancing qualities. Hardwood bark makes very good, inexpensive mulch, especially when it contains a blend of bark, wood, and leaves.
  • Mulch can be applied to landscape trees at just about any time of the year. However, the best time to apply mulch is in the middle of spring, once soil temperatures have warmed enough for root growth to begin.
  • Mulch as much of the area as possible, preferably to the outermost edge of the tree's canopy, referred to as the “drip line." Keep in mind, the drip line moves out as the tree grows.
  • Apply a 2- to 4-inch layer of organic mulch and no more; use less if the soil is poorly drained. More than 4 inches may harm the tree's root system. If using finely textured or double-shredded mulch, use 1 to 2 inches since these materials allow less oxygen through to the root zone.
  • For tree health, keep all mulch material away from the trunk. Allow the root flare (where the trunk meets the soil) to show. The root flare is at or near the ground line and is identifiable as a marked swelling of the tree's trunk where roots begin to extend outward.

This is a properly mulched tree. Note the mulch is only a few inches deep, not mounded around the trunk. The root flare is visible and the mulch extends to the edge of the tree's crown, or the drip line.

Other tips

  • Finely shredded mulches decompose faster and require replenishing more often.
  • Before replenishing the mulch each season, check the depth. Some old mulch may need to be removed before adding a new layer.
  • Applying new mulch over old mulch in successive years is the same as applying too deep a layer all at once.
  • The appearance of old mulch can be “refreshed" by breaking up any matted layers by hand or with a rake.

On newly planted trees, mulch more than just the root ball. The goal is to promote root development away from the tree. Mulch wide, not deep.

Avoid Overmulching

Overmulching landscape trees is common. This is most obvious when mulch extends up the trunk, smothering the root flare and root zone. This practice, known as “volcano" mulching, is never recommended and should not be utilized. As beneficial as mulch is, too much mulch is harmful. Deep mulch may suppress weeds, but it wastes time and money and can cause major health problems that lead to tree decline and possibly death.

Avoid piling mulch in the appearance of a volcano cone around trees. Volcano mulching, or piling mulch against the trunk, can cause major tree health problems.

Problems Associated with Overmulching

  • Oxygen starvation and root suffocation. Tree roots need oxygen to grow and function properly. When too much mulch covers the soil surface, air may not penetrate the mulch layer and the underlying soil becomes depleted of oxygen. In addition, excessively deep mulch can inhibit water loss through evaporation. Once soil pore spaces become filled with water, diffusion of oxygen into the soil is essentially blocked. When soil oxygen levels drop too low, root growth declines, making it impossible for the plant to take up water and nutrients. Plant death may result if too many roots decline.
  • Inner bark death. The inner bark, also called the phloem, carries photosynthates produced by the leaves to the rest of the tree. When mulch covers the root flare and trunk tissues, they stay constantly wet. This tissue is much different from root tissue and cannot survive under these conditions. Continuous moisture also interferes with respiration by limiting gas (oxygen and carbon dioxide) exchange between living cells in the trunk and the atmosphere. If wet conditions continue long enough, phloem tissue dies and roots are starved of essential carbohydrates.
  • Disease. Most fungal and bacterial diseases require moisture to grow and reproduce. Overmulching creates conditions where trunk diseases can gain entry through constantly wet, decaying bark, especially if there are trunk wounds under the mulch. Once established, these plant pathogens can cause fungal cankers and root rots. Cankers caused by these diseases can encircle the tree, killing the inner bark, ultimately starving the roots, and possibly killing the tree.
  • Insects. Mulch piled against the trunk favors moisture-loving insects, such as carpenter ants and termites, which could colonize and expand decayed areas of the trunk.
  • Rodent damage. Voles and mice may tunnel under deep layers of mulch for shelter. These pests may gnaw on the nutritious inner bark of young trees, girdling the stem. If girdling is extensive, tree death may result. This often goes unnoticed until the following spring when the tree doesn't leaf out.
  • Excessive heat. Similar to composting, thick layers of wet mulch may heat up once decomposition begins. Temperatures within mulch piles may reach as high as 140 degrees. This high heat may directly kill the inner bark/phloem of young trees or delay the natural hardening-off period that plants must go through in preparation for winter.

Correcting Overmulched Trees

If you believe you have a problem with overmulched trees, carefully dig with a hand trowel to assess mulch depth. Remember, 2 to 4 inches of mulch is sufficient on well-drained soils, less on poorly drained soils. A light raking of existing mulch may be all that is necessary to freshen old mulch and break through the crusted or compacted layers that can develop.

If mulch is piled against the trunk of the tree, visually look for the presence of the root flare where the tree meets the soil line. If the flare is buried, it is essential to uncover it. Begin by carefully pulling mulch back from the tree's trunk until the root flare is exposed, taking care not to damage the bark. A good rule of thumb is to pull mulch 3 to 5 inches away from young trees and 8 to 10 inches away from mature trees. Spread excess mulch evenly out to the tree's drip line, checking to ensure the depth does not exceed 4 inches. Research has shown that most trees respond rapidly with improved color and vigor once the root flare is exposed and excess mulch is redistributed.

Below is a series of photos showing where excessive mulch was pulled back from the trunk of a young red maple and redistributed to the tree's drip line. No mulch was removed from the site; it was simply spread out to the proper depth and kept from directly touching the tree's trunk. It is important to note that the amount of mulch used to create the mulch “volcano" was sufficient to properly mulch the tree.

Excessively mulched tree with mulch piled against trunk.

Hand trowel used to pull mulch back and redistribute.

Tape marking the original depth of the mulch.

Excess mulch spread evenly, 2–4 inches deep, out to tree's drip line.

Mulch pulled back from trunk, exposing the root flare.

Tree properly mulched using the same amount of mulch.

A word of caution: you may want to consult with a certified arborist before proceeding with any root flare excavations. Trees are often planted too deep and may have the root flare buried under soil rather than just excess mulch.

In Summary

  • Mulch out, not up! No deeper than the heel of your hand, generally 2-4 inches. Mulch less if soil is poorly drained or using finely textured mulch.
  • Back off from the trunk! Keep all mulch away from the trunk of the tree, allowing the root flare to show just above ground level.
  • Mulch to the tree's drip line, if possible! Remember, the drip line moves out as the tree grows.
  • Go organic! Arborists recommend organic mulches. They provide tree health benefits as they decompose.
  • Keep the trunk dry and the roots moist!

How to Mulch Around Trees

By

David Beaulieu

David Beaulieu

David Beaulieu is a landscaping expert and plant photographer, with 20 years of experience. He was in the nursery business for over a decade, working with a large variety of plants. David has been interviewed by numerous newspapers and national U.S. magazines, such as Woman's World and American Way.

Learn more about The Spruce's Editorial Process

Updated on 11/18/21

Reviewed by

Andrew Hughes

Reviewed by Andrew Hughes

Andrew Hughes is a certified arborist and member of the International Society of Arborists specializing in tree heal care. He founded and runs Urban Loggers, LLC, a company offering residential tree services in the Midwest and Connecticut.

Learn more about The Spruce's Review Board

A "mulch volcano" like this one is to be avoided. David Beaulieu

Homeowners frequently wonder, "Should I be using mulch around trees? And, if so, are there any rules to follow?" Using mulch around trees—particularly young trees—can be beneficial. However, there are some do's and don'ts to keep in mind when using garden mulch around trees.

Avoid Mulch Volcanoes and Collar Rot

"Mulch volcano" is a derogatory nickname that describes the excessive use of mulch around a tree. You have probably seen them on people's lawns and in public spaces, since, misguided as they are, they are very common.

A mulch volcano is usually the result of folks building circular raised beds around their trees, then filling the raised beds with mulch. The mulch gets steeper and steeper the closer it gets to the tree, which shoots out of the middle like a lava eruption. In such an arrangement, the mulch maybe two inches high at the perimeter and six inches high up close to the trunk. You might also see a mulch volcano springing out of the grass in the middle of a lawn.

There are several problems with mulch volcanoes as well as dirt mounded around trees:

  • Water runs off the sides of the mulch volcano and away from a young tree's base (which is where all of its roots are, for now), thus depriving it of water.
  • Six inches of mulch is too deep. Much of the water that would otherwise reach the tree's roots gets trapped in the mulch.
  • Excessive mulching can suffocate a tree's roots.
  • Deep mulch can invite rodent pests (such as voles) and diseases.

The biggest issue with improper mulching is that it retains moisture at the base of the tree, which will introduce collar rot. Collar rot occurs at the soil line where the plant emerges. The smartest thing you can do when you mulch is not let any mulch touch the trunk of the tree.

Benefits of Mulching Around Trees

Trees, especially young ones, typically benefit most from a 2- to 3-inch layer of mulch around their base. However, for the first 12 inches immediately surrounding the trunk, thin the mulch layer so that it just covers the soil. This will prevent the common problems associated with excessive mulching. Mulch should never touch the trunk of the tree.

Mulching trees keeps down weeds, thus eliminating competition for water and minimizing the number of encounters with a lawn mowers or trimmers that could damage the trunk. In addition, much of the water that otherwise would be evaporated by the sun can soak down through a 2-inch layer of mulch and into the soil around tree roots. Mulching trees helps insulate roots from extreme temperatures, keeping roots cooler in hot weather. It also helps prevent soil erosion in some cases, such as when on a hillside. Mulch works as a slow-release fertilizer, which is especially helpful when you clean up leaves from the ground in the fall.

Types of Mulch for Trees

You can mulch around trees with standard bark mulch, or you can use wood chips or shredded leaves. There is nothing wrong with using wood-chip mulches as long as you age them first. If you decide to apply a leaf mulch, use shredded leaves whenever possible because they break down more quickly than whole leaves, thus releasing nutrients more quickly. This is particularly beneficial to young trees. The only drawback is that faster decomposition means you will have to replace the mulch sooner.

When you rake up your leaves in fall, put them through a leaf shredder or leaf vacuum. Otherwise, shred the leaves by running the lawn mower over them and collecting them in the mower bag.

Watch Now: How to Prune a Tree

How to mulch tree trunks

Tree roots need regular watering, feeding, protection from drought and frost. Mulching the trunk circle is an effective way to preserve moisture and nutrients in the soil, suppress weed growth, and protect roots in winter. Mulch components enrich the earth with organic residues, prevent erosion, soil erosion, attract worms and beneficial insects.

With so many mulching materials, it can be difficult to choose the right ones for mulching the soil around trees. The choice of this or that material depends on the desired result: protection from heat and cold, soil nutrition, garden decoration.

Types and properties of mulch for trees

All types of mulch that are used in home gardens are divided into 2 types: organic and inorganic.

Organic mulch is based on processed natural materials. Its important property is the enrichment of the earth around the trunks with nutrients. Coniferous needles, cones, sawdust, bark, branches, straw, hay, rotted manure and compost are used to cover the trunk circle of trees.

Needles improve soil ventilation, drainage, repel rodents, increase soil acidity. The resins contained in it slow down the metabolic processes in the soil.

Sawdust, bark, wood chips, small branches improve soil aeration, increase its acidity, retain moisture and snow, and prevent nitrogen penetration into the soil. They are used after two years of exposure to sand and nitrogen-containing fertilizers.

Hay, straw, cut grass rot quickly, supply the soil with organic matter, contain plant seeds. Small rodents and insects often start up in hay, which harm trees.

Compost is organic remains of sawdust, wood shavings, leaves, wood chips, vegetables, and fruits that have rotted for two or more years. It is considered the best type of natural mulch.

Inorganic mulch does not rot. It is reusable and has protective and decorative properties. These are stones, pebbles, gravel, crushed stone, broken bricks, agrofibre, paper, cardboard. These materials do not feed the soil, but retain and pass moisture, improve the appearance of the site, and prevent the growth of weeds. To feed the roots, inorganic mulch is removed from under the trees, tree trunks are fertilized, loosened, and then returned to its original place.

Features of the use of mulch

For coniferous and fruit trees that do not require organic top dressing, use inorganic mulch. It suppresses the growth of weeds, passes moisture to the roots, creates an attractive appearance of the site, protects the roots from frost. In the near-stem circles of such trees, bright flower beds are broken, which do not require careful maintenance, create a good mood.

Needles and waste from wood processing increase the acidity of the soil. They cover the soil around the apple tree, quince, dogwood, which give a high yield on acidified soils. Plums and cherries grow well on neutral soils, so they should be carefully mulched with needles and sawdust. Alkaline soil is loved by tall and white plums, mountain ash, yew berry, viburnum, so needles and wood chips are not suitable for them.

Organic materials are used to protect and fertilize the soil around trees. Decomposed compost, manure is the perfect mulch for this occasion.

Rules for mulching near-stem circles of trees

Usually, near-stem circles are covered in spring, when the soil around the trees has already warmed up, dried up, and the first shoots of weeds have appeared. First, they clean and burn last year's organic mulch, in which insects, rodents, putrefactive bacteria have taken refuge for the winter. Then they loosen, fertilize the near-stem soil, pour fresh mulch. The diameter of the circle should be approximately equal to the diameter of the tree crown.

The effectiveness of mulching depends on the thickness of the layer. Too thick a layer will lead to decay, too thin - to the development of weeds and loss of moisture. The optimal thickness is 3–7 cm. The heavier the soil, the smaller the mulch layer. The height of the layer depends on the type of material:

  • needles - 3–5 cm;
  • sawdust, shavings - 3–7 cm;
  • bark - 3–5 cm;
  • hay, straw, grass - 7-15 cm.

Too early spring mulching slows down the awakening of plants from hibernation. Mulching immediately after heavy rains is not recommended, because pathogenic microorganisms, fungi, slugs quickly develop in dampness. Not rotted manure and compost causes burns and death of young seedlings.

Autumn mulching is carried out in regions with cold winters to protect the roots from freezing, to delay the snow cover around the trees. It is impossible to lay a layer of mulch on frozen ground.

Proper application of mulching improves the growth and yield of trees on the land. This is an effective way to protect and decorate the garden.

Mulching fruit tree trunks

Mulching is one of the simplest and most inexpensive agricultural practices used to increase the yield of fruit trees.

Mulch is a material used to cover the topsoil to protect it. Mulch can be organic - grass, compost, manure, peat, straw, conifer bark, wood chips, shavings, dry leaves, needles and other similar materials. And inorganic - plastic wrap, pebbles, crushed stone, lutrasil, fragments of bricks.

Both organic and inorganic mulches have a number of useful properties:

  • Prevents soil erosion;
  • Retains moisture, eliminating the need for frequent watering;
  • Relieves the damaging effects of heavy rains;
  • Stabilizes the soil temperature at the same level;
  • Inhibits the growth of near-stem weeds;
  • Prevents the formation of dirt after rains;
  • Keeps the garden in a "marketable" form.

Organic mulch also improves soil texture. Since such a mulch slowly decomposes, it gives some of the nutrients to the soil in the near-stem circle of the tree. As a result, root growth, soil permeability and its ability to retain moisture increase. The organic compounds contained in the mulching material promote the growth of trees, attracting earthworms and other organisms beneficial to the garden.

Inorganic mulch also has a number of advantages, in particular - high decorative qualities. However, such mulch does not improve the quality of the soil, and it can be quite difficult to remove it from the site in case of a radical change in the garden plan. Thus, the use of organic mulch in many cases remains more appropriate.

Where to get material for mulch

Different types of mulch are used in different conditions, depending on what the goals are: to cover the surface of the tree circle from the sun, improve soil structure around the tree, increase nutrient content. Whatever the goal of the gardener, the available variety of mulching materials can satisfy any of his needs. And as a rule, these materials are widely distributed and more than available.

Most of them can be found in your own garden! For example, cut grass is perfect as a mulch, in fact, it is most often used.

Excellent and very affordable material - plain newsprint. It is used in combination with other types of mulch, in itself has the ability to drain the soil.

Pine bark and tree leaves are not only affordable material, but also an excellent option for improving soil structure - increasing its ventilation and drainage. The same can be said about compost, if it is in sufficient quantity, then this material will not only improve the structure of the soil, but also supply it with nutrients.

Bark mulch can be used as a decorative cover. Depending on the size of the pieces of bark, it can last a very long time, but this mulching material is best for trees that prefer an acidic soil.

Depending on where you live, a wide variety of materials can be used as mulch. Hay and straw work great in the garden, although they can be a source of weed seeds. Mulch made from seaweed or pine needles is also a good material. Although needles also contribute to an increase in soil acidity.

Best type of mulch

In most cases, the best type of mulch for trees is wood chips. This mulch, gradually decomposing, dosed, supplies the roots of fruit trees with additional nutrients. At the same time, wood chip mulch is an excellent barrier to weeds, which also helps to improve the microclimate around the root system of the tree.

Mulch thickness, depending on the material used

Type of mulch layer thickness, (cm) Note
coniferous cows 5 - 10 Nice material for mulching soils around the trees and soils. Well prevents evaporation of moisture.
Wood chips 5 – 10 Similar to bark. Together with a large number of leaves and pre-composted, it is an excellent material
Leaves 7.5 – 10 Compost before use. Dry leaves are effective when applied in a 15 cm layer. It is better to dry before use. Do not use grass from lawns treated with herbicides.
Paper 0.5 Sheets of newsprint or cardboard are used in combination with other materials, while the layer of these materials can be made smaller.
Chip and sawdust compost 7.5 – 10 Excellent material for mulching garden trees.

An even better solution, from a nutritional point of view, is wood chip and sawdust compost. For a long time, wood chips are subject to decomposition, during which the soil is supplied with nutrients. But in the struggle for these nutrients, quite a lot of competitors are involved, in the face of various microorganisms. As a result, the soil of the near-trunk circle of the tree does not receive all the nutrients that it could. The solution to this problem is - compost from wood chips and sawdust. Preparing such a mulch is quite simple. The main thing is to ensure that the composting container is well ventilated and its contents are mixed frequently enough.

Video: How to mulch trees properly

Other types of organic mulch, such as conifer bark, may be suitable for mulching fruit trees.


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