Mulching Around Trees: Properly Mulching Shrubs & Trees By Type, Zone

New gardeners and homeowners often wonder, is mulching around trees beneficial? And, if so, are there any rules to follow?

Mulching trees, especially young trees, is quite beneficial because it protects the roots from harsh climate changes, helps retain moisture and provides nutrients for the plant.¹ Therefore, mulching helps promote the growth of young trees.

Once you’ve discovered the benefits of mulching,⁷ you need to learn about the do’s and don’ts of the process because there are certain rules to follow. Otherwise, if you ignore these rules, you could kill your shrubs and trees with improper mulching techniques.

The following guide explains the rules on how to properly mulch shrubs and trees according to different zones and types as well as the pros and cons of mulching around trees when gardening.

Tree Mulching: What Is Mulch?

Tree mulching is both decorative and functional, but what is mulch?³

Mulch typically refers to an organic or sometimes inorganic material that is spread on the surface of the soil to protect roots from drought, cold, heat, and other harsh environmental conditions.

Additionally, organic mulch provides nutrients to trees and plants as it decomposes.

Mulching also:

• Protects plants from lawn equipment and foot traffic
• Improves the condition of the soil
• Enhance the beauty of the landscape
• Suppresses weeds

Mulching Benefits (Pros of Mulching Around Trees)

Mulches improve the fertility and structure of the soil and this is very crucial in urban landscapes where you can find compacted soil which lacks organic matter especially near construction sites.²

Mulching around trees usually mimics the natural forest environment where branches and leaves fall and add a blanket layer to the soil surface.

This layer replenishes soil nutrients as the organic matter decomposes and this leads to an ideal environment for root growth.¹²

Trees and shrubs that grow in urban landscapes usually have to live in harsher environments where human activities, such as lawns, construction, and compaction, have modified the soil. Adding just two inches of mulch re-creates the same conditions as forest soil environments.

Many experts will tell you that mulching around trees, when done correctly, is among the most beneficial practices a gardener or homeowner can do for the tree’s health.

Mulching is a standard practice in the horticulture industry and it helps to minimize soil erosion, conserve soil moisture, and reduce weeds. It’s also a better alternative to planting shrubs, grass, or ground cover near the tree because it reduces the competition for moisture and nutrients.

Mulching benefits do not stop there. It also moderates the temperature of the soil, reduces soil compaction, and protects the plants from equipment injury from weed trimmers and lawnmowers.

What’s more, those are not the only reasons to mulch shrubs and trees, you can do it to facilitate the growth of the root system of the different types of trees.

Lastly, you can mulch young trees for aesthetic reasons. In this case, you apply your favorite mulch to get the look you desire but it’s important to refrain from over mulching.

Over-Mulching Disadvantages (Avoid ‘Volcano’ Mulching)

You’d be surprised how common over-mulching of landscape trees is.⁸

One obvious sign is when the mulch goes up the trunk of the tree and in the process, it smothers the root zone and the root flares. The name of this practice in volcano mulching.

Experts and novice gardeners alike do not recommend this method and it should not be used. Even though mulch is beneficial, too much of it is dangerous.

While deep mulch prevents the growth of weeds, it’s a waste of money and time and causes major health problems for the tree or shrub. Their health can be severely affected and eventually, in the worst case scenario, it will lead to death.

Most tree types such as hardwood, evergreens, vines plants, and shrubs require mulching that is a few inches away from the base of the tree. Additionally, privacy trees with protruding roots require space beneath the mulch.

Avoid piling mulch until it looks like a volcano around the tree. Volcano mulching, or over-mulching has several disadvantages they include:

Root Suffocation and Oxygen Starvation

The roots of trees need oxygen for proper growth and function. When you cover the soil surface with too much mulch, it makes air penetration very difficult and causes depletion of oxygen in the underlying soil.

Moreover, deep mulch that is excessive can inhibit natural water loss through evaporation. When watering a tree, the pores of the soil get filled with water, and this blocks the oxygen diffusion in the soil.

As a result, the growth of roots declines because the soil has low oxygen levels. It’s also impossible for the plant to take up nutrients and water and if too many roots decline, the plant will die.

Inner Bark Death

The phloem or inner bark transports photosynthates created by leaves to the other parts of a tree.

When mulch covers trunk tissues and root flare they remain constantly wet. This tissue is not the same as root tissue and cannot properly function under these conditions.

This continuous moisture also interferes with the tree’s respiration by preventing gas exchange between the trunk’s living cells and the atmosphere.³ If the phloem tissue is left in the wet condition for a long time, it will die and the roots will be starved of carbohydrates essential for the growth and functioning of the tree.

Disease

Bacterial and fungal diseases need moisture to reproduce and grow.

Over-mulching creates the perfect conditions for trunk diseases to enter the tree through the constantly wet, decaying bark. The bacteria and fungi enter the tree from the trunk wounds inside the mulch.

Once the plant pathogens are established, they create root rot and fungal cankers. The cankers then encircle the tree and kill the inner bark, starve the roots and eventually kill the tree.

Insects

If you pile mulch against the trunk, it favors insects that love moisture such as termites and carpenter ants. These insects can colonize and expand the trunk’s decayed areas.

You will have to learn how to get rid of aphids to protect the life of your tree.

Rodent Damage

Mice and voles create tunnels under the deep mulch layers to make shelters. These pests may feed on the inner bark of young trees that are nutritious to them.

The feeding girdles the stem and if this girdling continues it can result in the death of the tree. In some cases, the death will go unnoticed until some signs of tree not growing leaves in spring show.

Excessive Heat

Heavy layers of wet mulch may produce excessive heat during the decomposition process. Piles of compost can generate temperatures as high as 140 degrees.

The high heat can kill the phloem of a young tree or prevent the natural hardening-off that trees go through in preparation for winter.

Types of Mulch: What Are the Commonly Used Mulch for Trees?

There are two types of mulch; organic and inorganic. Organic mulches include:

Bark

You can get softwood (pine-bark) mulches because they have a pleasant appearance, are slow to decompose and are readily available. Bear in mind that they cost a lot more than shredded hardwood.

Mulches of hardwood bark are also readily available and cheaper than pine-bark mulches. However, hardwood barks may have high manganese levels which can be toxic to plants in soils with a pH lower than 5.0.

Bark mulches are applied 1-3 inches deep.

Wood Chips and Sawdust

Sawdust is applied 1-inch-deep while wood chips are applied 1-3 inches deep. You can get sawdust and wood chips at low cost, or for free from a local tree trimming or removal company or from local sawmills.

You can use wood chips fresh from the arborist as mulch around shrubs and trees as long as you do not incorporate them into the soil. Arborist wood chips are not recommended around vegetables and annuals.

Sawdust and wood chips (to a lesser extent) deplete nitrogen from the soil. If you work them into the soil, you should examine the color of the foliage and growth of the plants that have been mulched with these two materials.⁴

If the plants experience slow growth or become chlorotic, then you should apply 1-2 pounds of nitrogen per 1,200 square-feet of garden area.

Pine Needles

The other name for pine needles is pine straw.⁹ They are a great mulching material because they are attractive, add fragrance to the garden, and are slow to decay.

You should apply only 2-3 inches of pine needles layer.

Grass Clippings

You should apply 1-2 inch layers of grass clipping as mulch. It’s typically recommended to leave grass clippings on the lawn once you’ve mowed it to allow decomposition.

However, grass clippings can be used as mulch or composted. They have a rapid decomposition rate and must be regularly replaced.

Take care to avoid clippings that have weed seeds. You should not use clippings from lawns that have been treated with herbicides or a combination of herbicides and fertilizer.

Leaves

Leaves, especially when shredded, make excellent mulch. They have a quick decomposition rate which improves the soil condition.

You should apply a 2-3 inch layer.

Compost

This material should be applied on a 1-inch layer. It makes excellent mulch and continuously decomposes improving soil conditions.

If you add compost regularly (in this case annually) you will strengthen the structure of the soil.

Some inorganic mulches include:

Lava Rock, Stone, and Gravel

These mulches are applied in a 1-inch layer. They provide mulches that last a long time and are particularly useful in special plantings such as alpine and rock gardens.

Lava rock is red and weighs less than stone or gravel. You can use this material instead of plastic or fabric.

However, you should avoid using limestone mulches because they can change the pH of the soil.

Landscape Fabric

These are synthetic materials that preserve the moisture of the soil and prevent weeds from growing. There are two forms of landscape fabric;¹⁰ spun-bonded and woven.

The woven materials can look like burlap or have a fine screen texture. On the other hand, the spun-bonded materials have a fibrous texture and are used mostly on slopes.

You cover both materials with a layer of stone or bark in the landscape. The fabric mulches collect soil and organic debris over time.

The seeds of weeds can germinate in the debris and soil collected and their roots can penetrate the fabric. These weeds are often difficult to remove and therefore, it’s important to pull the weeds before maturation and seed production.

Cut away, or remove any synthetic landscape fiber near the base of the tree roots. Otherwise, it can cause the development of girdling roots.

This restricts normal growth of roots and eventually leads to tree decline.

Best Mulch For Mulching Around Trees

Between the two types of mulches, organic and inorganic, tree care professionals or tree doctors recommend organic mulches.⁴

Wood chips, saw dust, compost mixes, leaves, cocoa hull, pine needles, and hardwood and softwood barks are the best mulch for trees. They decompose and improve soil structure eventually adding to soil fertility.

The different kinds or organic mulches have different decomposition rates and require regular reapplication. In contrast, inorganic mulch such as gravel, is only applied once but does not provide the same benefits as their organic counterparts because they do not decompose.

How To Mulch Around Trees

These are the steps to take when mulching around trees:

Step 1: First, you should shovel away weeds, grass, rocks, and old mulch around the base of the tree to prepare the tree’s root flare for a fresh coating of mulch.

Step 2: Choose a medium-textured mulch. Tree professionals do not recommend fine textured mulch because it gets compacted and starves the roots of the trees of oxygen.

On the other hand, coarse mulch is too porous and cannot maintain adequate levels of moisture. In contrast, mulch that is medium textured retains water and at the same time provides the roots with adequate oxygen making them a perfect mulching material.

Step 3: Spread the mulch in a diameter of 4 to 5 feet around the tree.

The mulch should be thin, around 1 to 2 inches deep and you should also place a 2-inch space between the base of the tree and the mulch.

Mulching Ideas

Some mulching ideas include:

• Tree experts recommend getting organic mulches because they have soil-enhancing qualities. If you want good and inexpensive mulch, then you should get hardwood bark.
  Make sure you pick the kind that is a mix of leaves, wood, and bark.
• You can apply mulch to landscape trees at any time of the year. However, the most recommended time is usually in the middle of spring when the temperatures of the soil are warm enough to facilitate root growth.⁵
• You should add mulch to as much of the area as possible, especially on the outermost edge of the canopy of the tree (the drip line). Bear in mind that the drip line will continue to move as the tree grows out.
• Only apply a 2-to 4-inch layer of organic mulch. It should be no more than 4 inches because it will make the soil poorly drained.
  It may also harm the root system of the soil. The best mulch to use is medium textured to allow adequate oxygen to get in the soil and prevent water saturation in the soil.
• For the health of the tree, keep all the mulch away from the trunk. Make sure that the root flare (where the tree meets soil) is showing.
  This root flare is usually at or near the ground line. It is usually the marked swelling of the trunk of the tree where the roots start to extend outwards.

Mulch Rings for Trees

Mulch rings for trees, also called mulch discs, give trees and shrubs a wide range of benefits.¹¹ They are made from durable coir fibers and fit easily around the base of the tree.

These tree rings create defined borders around the base on the trees and help protect them from physical damage.⁶ They also ensure that the root ball of a young tree has access to nutrients and water and is away from the competition of other plants.

The design and construction of a mulch ring can affect the health and growth of the tree.

Most trees have shallow roots and grow near the surface of the soil. These roots usually extend past the drip line of the soil and can grow as long as the tree is tall.

The digging should be shallow to prevent damaging the roots.

Mulch rings are not dug just for aesthetics; the ring should extend to the drip line of the tree. If this is not feasible, anything with a diameter of 4 feet could work.

You should mulch the trees with organic mulch to retain moisture and enhance the structure of the soil.

It’s important to note that rubber mulch rings are not as effective as natural mulch and they can damage your tree.

Overtime, as the rubber breaks down, it releases toxic contaminants into the soil. They can also slow the growth of the tree and turn the leaves yellow.

Mulching Around Trees: How Deep Should Mulch Be?

The mulch should be spread about 2- to 4-inches thick. This largely depends on the type of mulch.

If the mulch is too thin, weeds will push through and if the mulch is too thick water will not reach the soil. The table below shows the types of mulch and how much you should apply.

Mulching Around Trees: When To Put Mulch Down

Most people make the mistake of mulching the soil when the weather gets warm. Even though the best time to mulch is during warm weather, you should never mulch in early spring.

First, you must give the soil a chance to get warm. If you mulch too early, you slow down the warming process.

Generally, the best time to mulch young trees is mid to late spring.

Seedlings can make their way through thin layers of mulch so be careful not to add thick and impenetrable layers of mulch.

You should allow the plant to get off to a good start before adding the mulch. Once the tree is established, you can add more mulch.

Besides spring, you can apply additional mulch in the winter as heat insulation or in the summer to retain moisture. Even so, if you provided a layer of mulch for the winter, you should pull it away gradually as warmer temperatures arrive.

The word here is gradually because if you remove mulch at once, the new growth underneath that is tender could be impacted by a late season cold snap.

Fall Mulching

Fall mulching works the same as spring mulching.

It helps retain the moisture of the soil and suppresses the growth of weeds. It also protects the soil from erosion.

If you mulch in the fall, you insulate the soil creating a warm environment for the soil’s ecosystem. Since the soil is warm, organisms such as microbes and earthworms remain active longer improving your soil in the process.

The roots of the plants are also insulated against the harsh winter climates. Fall mulching is recommended in areas where the soil freezes solid in the heart of winter.

Best Mulch for Fruit Trees

Tree care professionals recommend wood mulch and compost as the best mulch for fruit trees. This mixture provides nutrients, prevents weed growth, and increases moisture retention.

You should also use green waste compost instead of manure compost. This is because the manure compost causes excessive vegetative growth as a result of high nitrogen levels.

How To Keep Mulch From Washing Away

If you want to prevent mulch from washing away, you should take the following steps:

1. Use fine-textured organic mulch because they are difficult to wash away
2. Do not use underlays like plastic sheeting and landscape fabric
3. Create terrace slopes or use living mulch ground covers for areas that are gently sloping
4. Add perimeter plants, landscape edging material or a trench to the edge of the landscape
5. Add a low-growing groundcover plant to hold the mulch in place

To summarize, mulching is very important to young trees and trees growing in urban landscapes. This is because the mulch mimics the ground cover of trees growing in forested areas.

Mulching around trees also protects the roots from harsh climates, weeds, and loss of moisture.

Frequently Asked Questions About Mulching Around Trees