How do I mulch a tree properly?
Spread mulch 2–4 inches deep in a flat ring, kept 3–6 inches away from the trunk so the root flare stays exposed, out to the drip line or at least 3 ft across. Shredded bark or wood chips are best. Refresh once a year, only enough to get back to 2–4 inches. Never pile mulch against the trunk.
Mulching is the cheapest thing you can do for a tree and the easiest to get wrong. Done right, a mulch ring keeps soil moist, keeps the mower away from the bark, stops grass competing with young roots, and builds the soil. Done wrong, it is a slow killer. Any subdivision shows the wrong way: a cone of dyed mulch heaped against the trunk. Arborists call it a mulch volcano and remove trees every year that it killed.
| Right | Wrong | |
|---|---|---|
| Depth | 2–4 inches, level | 6 inches or more, mounded |
| At the trunk | 3–6 inches of bare ground; root flare visible | Mulch piled against the bark |
| Width | Out to the drip line, or at least 3 ft across | A 1 ft circle, or none |
| Shape | Donut: flat ring with a hole in the middle | Volcano: cone with the trunk at the peak |
| Material | Shredded bark, arborist wood chips, pine straw, pine bark | Rock, rubber, dyed mulch of unknown source, fresh grass clippings |
| Under the mulch | Soil, or cardboard to kill turf | Landscape fabric or plastic |
| Refresh | Once a year, only enough to get back to 2–4 inches | A full new layer every year on top of the old |
| Cost | Bagged mulch $3–$6 per 2-cubic-foot bag; arborist chips often free | — |
How do I mulch a tree, step by step?
- Find the root flare. Clear grass, soil, and old mulch from the base until you see the trunk widen into the roots. If the tree was planted too deep, this may be a few inches down. The flare stays in the air.
- Mark the ring. Go out to the drip line if space allows, or at least 3 ft across for a young tree. Strip the turf with a flat spade or smother it with cardboard.
- Spread 2–4 inches. Lay shredded bark or wood chips 2–4 inches deep, level. Shallow end on heavy clay and fine mulch; deep end with coarse chips on sand.
- Pull it back from the trunk. Rake the mulch 3–6 inches away from the trunk on all sides: a donut with the trunk in the hole. Nothing touches the bark.
- Water it in. Soak the ring so it settles. If water beads on top and runs off, the mulch is too fine or too deep; rake it looser.
- Refresh once a year. Each spring, rake the old layer to break up crust, then add only enough to return to 2–4 inches.
Why is a mulch volcano bad for a tree?
Because bark is not meant to be buried. Mulch against the trunk holds moisture on it around the clock, the bark softens and rots, and decay fungi and borers get in. At the same time, roots grow up into the moist pile instead of out into the soil, wrap around the trunk, and as both thicken they girdle the tree and cut off its own water supply. The tree looks fine for years, then thins from the top and dies in a drought, and nobody connects it to the mulch. A deep cone also sheds rain and blocks air from the roots. If you have a volcano now, rake it down to 2–4 inches, pull it back 3–6 inches, and expose the flare; if roots are already circling the trunk, an arborist can cut them while it is still worth doing.
How deep should mulch be around a tree?
2–4 inches once it settles. That is deep enough to shade out weeds, hold moisture, and buffer soil temperature, and shallow enough for air and water to get through. On heavy clay that drains slowly, stay at the shallow end; on sand, go deeper. Fine, shredded mulch packs down and should be thinner than coarse chips. Past 4 inches it acts like a lid, holding too much water in wet weather and repelling it in dry. Most roots are in the top 12–18 inches of soil, and what they need from mulch is a moist, breathable surface. A ring at the right depth also makes watering more effective, because water soaks in instead of running off dry bare soil.
What kind of mulch is best for trees?
Shredded hardwood bark or arborist wood chips. Both are coarse enough to breathe, break down over a couple of years, and feed the soil as they go. Arborist chips, the mix off a chipper, are often free from local tree crews and are what most arborists put on their own trees. Pine straw and pine bark are fine where they are the local standard. Avoid rock, which heats the soil; rubber, which does nothing for it; and dyed mulch from an unknown source, which can be ground pallets and treated lumber. Never lay landscape fabric or plastic under mulch; roots end up growing on top of it. Chips from a stump grinding are fine once raked out; see can I plant where a stump was ground?
How often should I add mulch?
Once a year, in spring, and only as much as it takes to get back to 2–4 inches. Rake the old layer first to break up the crust that forms on fine mulch, then top it up, which most years means an inch or less. The mistake is putting a full fresh layer over the old one every year, which is how a 3-inch ring becomes a 10-inch volcano in a few seasons. Bagged mulch runs $3–$6 per 2-cubic-foot bag, so a ring on a young tree is a few bags a year. There is no need to fertilize under it; see do trees need fertilizer? A new tree should get its ring the day it goes in, as described in how and when should I plant a tree?
No independently confirmed professional review is on file yet.
Not yet independently reviewed. Figures are typical US ranges for planning purposes, not quotes.