What Mulch Does
In a forest, a tree sinks its roots into soil enriched with organic matter, microbes and vital nutrients. As leaves fall from trees and decompose, they replenish soil, creating a rich, fluffy, well-aerated base ideal for root growth.
The typical yard doesn't usually offer the same cozy amenities to tree roots. Soils are typically nutrient-depleted, short on organic matter and subject to temperature and moisture extremes. Mulch remedies these problems, along with others.
A Mulch Layer:
- Insulates soil and helps moderate temperature swings
- Slows water evaporation from soil
- Reduces soil compaction that occurs during hard rains
- Interferes with weed seed germination and reduces weed growth
- Makes weeds that do appear easy to pull
- Keeps fungal spores and other disease organisms from splashing from soil onto the tree
- Buffers trees from lawn equipment damage
- Gives planting beds a manicured appearance
- Protects against soil erosion and water runoff
Secrets To Mulching
It's not hard to succeed with mulch. Follow a few simple rules to give your trees the royal treatment.
When to apply – You can apply mulch any time of year, although it's nice to have it in place before summer heat arrives. In coldest regions, wait until soil warms in spring before applying (or refreshing) mulch.
Where to apply – Place mulch in a ring that extends outward from the trunk at least 3-6 feet. Some homeowners place mulch at least to the tree's dripline (the edge of the outermost leaves). It's okay to apply the mulch beyond tree's dripline, because roots extend beyond that point. It's also okay to apply it inside the dripline, especially with large, mature trees.Do not pile mulch directly against the tree trunk. Pull it back a few inches from the trunk, creating a doughnut-hole effect that allows air to reach the trunk. Remove existing turf or weeds before applying mulch.
How deep to apply – A good rule of thumb is to apply mulch 2-3 inches deep. With sandy, fast-draining soils, you may want to apply a layer up to 4 inches deep. On soils that drain slowly, you may only need a 1-2-inch layer.
How often to apply – Organic mulches, like shredded or ground bark, pine straw, compost, wood chips or cottonseed hulls, break down over time and need replenishing. Check mulch at least annually – twice annually in warmest regions. Refresh mulch as needed, but always check the existing depth before automatically piling on more.
In cold regions, refresh mulch as needed after the ground freezes to provide some winter protection, especially for newly-planted trees. Learn about other winter care tips for new trees.
Mulch Gone Wrong
A few myths persist about mulching trees. Avoid these common pitfalls when mulching your trees.
- Mound the mulch – Piling mulch into a volcano-shaped mound is frequently done, but it's damaging to the tree because the mulch is too deep.
- Pile it high – More is not better with mulch. Layers that are thicker than 3 to 4 inches can cause problems for tree roots and also lead to rot, disease or insect issues.
- Touch the trunk – Mulch heaped directly against the tree provides a hiding place for insects, rodents and diseases, which can attack the tree through the trunk.