Proper application of organic mulch provides excellent benefits. It is one of the simplest and most cost effective things a tree owner can do to improve their tree’s rootzone. It is important not to mound mulch against the trunk, as this will result in a buried rootflare and could also provide a habitat for bark-eating rodents. Do not incorporate fresh mulch into the soil (such as with vertical mulching or radial trenching) as the mulch will deplete available nitrogen in the soil as it breaks down. A 2-4″ top layer of organic mulch or wood chips will:
- Provide a protection layer against lawn mower injury and soil compaction by vehicles, equipment, and foot traffic
- Improve soil moisture retention
- Insulate the rootzone from temperature extremes
- Smother out turf grass, which competes with tree roots for nutrients and water
- Increase organic activity in the soil, to include essential mycorrhizal fungi, which are vital for a thriving rootzone
- Give nutrients back to the tree as it breaks down
- Improve rootzone aeration over time with organic activity
How to Apply Organic Mulch Correctly
Applying mulch the right way matters as much as the mulch itself. A few key practices make all the difference:
- Spread a 2-4″ layer evenly across the rootzone, extending outward as far as practical—ideally toward the dripline, where the tree’s feeder roots are most active.
- Keep mulch pulled back from the trunk by several inches so the root flare stays visible and exposed to air. A “donut” shape around the base is correct, while a “volcano” of mulch piled against the bark is the most common and most damaging mistake.
- Top up rather than bury. As the layer breaks down over time, refresh it to maintain that 2-4″ depth instead of piling thick new layers over old ones, which can lead to excess depth and poor aeration.
Choosing the Right Type of Organic Mulch
Several organic materials work well as tree mulch, and the best choice often comes down to availability and appearance:
- Arborist wood chips — the shredded mix of bark, wood, and leaves produced when trees are pruned or removed—are widely regarded as one of the best options because they break down into a balanced range of nutrients.
- Shredded bark and pine straw — common alternatives that resist washing away on slopes.
- Avoid fresh, undecomposed chips working directly into the soil, as noted above, and steer clear of inorganic options like rubber or stone if the goal is genuine rootzone health.
Whichever material you choose, the goal is the same: a natural, undyed organic layer that decomposes over time and feeds the soil.
