How To Properly Mulch Around a Tree

Mulching around your trees can offer many benefits, but only when you do it correctly. Improper mulching can, unfortunately, lead to serious tree health issues and even premature death.

In the video above, This Old House landscape contractor Roger Cook and certified arborist Matt Foti show how to save a tree from mulch suffocation and properly apply mulch. Below, we explore the proper techniques for mulching around trees, common mistakes to avoid, and expert tips to help your trees thrive.

The Importance of Proper Tree Mulching

Mulching, when done correctly, provides several advantages for trees:

• Moisture retention
• Protection from lawn equipment
• Soil enrichment
• Temperature regulation
• Weed suppression

Unfortunately, poor mulching techniques can do more harm than good.

The Dangers of Mulch Volcanoes

“Mulch volcanoes” happen when mulch is piled high against the tree trunk, resembling a volcano. This can cause:

• Bark decay
• Girdling roots
• Increased pest and disease susceptibility
• Root suffocation

Foti emphasizes that mulch volcanoes suffocate the root mass and cause the bark to deteriorate, which can kill the tree. Luckily, you can avoid this by applying mulch the right way.

Tools and Materials

Have the following tools and materials on hand: 

• Air spade
• Bypass lopper 
• Hand pruners 
• Shovel

How To Mulch Around Trees the Right Way

Follow these steps to ensure your trees get the benefits of mulching without the risks:

1. Remove old mulch and debris around the tree base.
2. Expose the root flare (where the trunk flares out at the base). Keeping this area visible is essential for tree health.
3. Remove girdling or upward-growing roots if you notice any.
4. Apply a thin layer of topsoil if the area needs leveling.
5. Spread mulch in a wide, even layer. It should extend far enough to cover the root zone.

Exposing the Root Flare

The root flare is the area where the trunk expands at the base of the tree. Keep this area exposed to keep the tree healthy. To uncover a buried root flare:

1. Use a shovel to carefully remove excess soil and mulch.
2. Employ an air spade or similar tool for stubborn or compacted material.
3. Prune away any secondary roots growing over the flare.

How To Properly Apply Mulch

When mulching around trees, the technique matters just as much as the material:

1. Extend the mulch out to the tree’s drip line (the outer edge of the tree’s branches) or beyond.
2. Keep mulch 2–3 inches away from the trunk to prevent moisture buildup and decay.
3. Maintain a depth of 2–4 inches of mulch for the best moisture retention and temperature regulation.
4. Use organic mulch materials such as wood chips or shredded bark.

Common Mulching Mistakes To Avoid

While mulching offers many benefits, certain practices can harm trees. Here are some common mistakes to steer clear of:

• Applying mulch over girdling roots, which can cause root damage.
• Failing to remove old mulch before applying the new.
• Piling mulch against the trunk (creating a mulch volcano).
• Using inorganic materials like rubber or rocks.
• Using too much mulch, which can suffocate roots.

Mulching Different Types of Trees

While the basic principles of mulching remain the same, different tree species may have specific needs.

Newly Planted Trees

Newly planted trees require careful attention to make sure they establish strong root systems. When mulching:

• Avoid disturbing the root ball when applying mulch.
• Create a wider mulch ring to encourage root spread.
• Monitor moisture levels closely to help the tree establish a strong root system.

Mature Trees

Mature trees benefit from mulching just as much as younger trees. Proper techniques include:

• Extending mulch to the drip line or beyond to cover the root zone.
• Removing grass and weeds before applying mulch.
• Using a leaf blower to spread mulch evenly around the base.

Fruit Trees

Fruit trees have specific mulching needs to promote healthy growth and fruit production:

• Adjusting mulch depth based on the tree’s water needs.
• Keeping mulch away from the trunk to prevent rodent damage.
• Using organic mulch to improve soil fertility and support fruit growth.

Maintaining Your Mulched Trees

Proper maintenance helps your trees continue to benefit from mulching:

• Check for signs of pest or disease issues regularly.
• Make sure the root flare remains visible and unobstructed.
• Refresh mulch annually, adding only enough to maintain proper depth.
• Remove any weeds or grass growing in the mulched area to prevent competition for water and nutrients.

When To Remove or Replace Mulch

In some cases, you may need to remove or replace existing mulch, specifically:

• If the mulch has become compacted or water-repellent.
• If the mulch has decomposed significantly.
• When changing to a different type of mulch material.
• When fungal growth is excessive.

Replacing mulch can help maintain an ideal environment for tree health.

Professional Tree Care and Mulching

While mulching can be a DIY project, sometimes professional help is necessary. Professional arborists can assist with:

• Compacted soil or buried root flares
• Large or valuable trees
• Suspected tree health issues

Professional arborists can help make sure proper mulching techniques are used to keep your trees healthy.

The Drawbacks of Mulching with Inorganic Materials

While organic mulch is generally preferred, you might use inorganic materials such as rubber or rocks. However, inorganic mulches can lead to various issues:

• Heat retention: Inorganic materials, particularly rubber, can retain and reflect heat. During hot weather, this can cause soil temperatures around the tree to rise significantly. Elevated soil temperatures can stress tree roots and potentially lead to heat damage.
• Lack of nutrients: Unlike organic mulch, inorganic materials do not decompose and add nutrients back into the soil. Organic mulches break down over time, enriching the soil with essential nutrients that support tree growth. Using inorganic mulch means missing out on this natural soil enrichment process.
• Root damage: Materials like rocks or plastic sheeting can compact the soil over time, blocking water penetration and air circulation. Proper soil aeration supports root health, and compacted soil can impede root growth and cause long-term damage to the tree’s overall health.