It is ideal to apply a 2”-to-3” layer of mulch around a tree that extends out to its drip line. This layer of mulch does a few things including:
- Prevents weeds
- Retains moisture
- Maintains consistent soil temperatures
- Provides a nice buffer between equipment (mowers, weed wackers, etc) and tree trunks
- Gives a finished look to the landscape
However, take care not to cover the base of the tree’s trunk and its root flare with mulch. The sapling in this photo was not mulched properly. It was “volcano mulched,” meaning the mulch was piled in a volcano shape right up to the bark of the trunk. If you pile mulch against the trunk, it will hold moisture there and may lead to root rot. It can also lead to the tree sending up secondary roots, which are weaker roots that will likely get zapped by the sun, frozen by frost, or strangle the tree. Not good. If you want to meet someone who hates volcano mulching with a passion, meet Ken Druse, a guru of gardening who has tons of tips to help you flourish in your landscape.
Instead, mulch your trees starting a few inches out from the trunk out to the drip line or beyond, as far as an 8-foot diameter. The root system of the tree extends far beyond its drip line. In a forest, that entire system benefits from naturally-occurring mulch.
Also, if you have old mulch around your trees, it may need to be raked to ensure it’s not matted. Otherwise, if it’s thick and matted water and air may not be able to seep through to the tree’s root system. Mulch that’s matted can also become weed-ridden.
Organic mulches usually need to be replenished a few times a year to ensure the right depth of mulch (roughly 3 inches) protects and nourishes your trees.
Check it out: In this video these guys identify mulch volcanos that are suffocating/disabling the trees, and save a few by removing a primary layer of mulch, then airblasting away the extraneous mulch, trimming away the secondary root structure, and re-applying a 2” layer of mulch (not next to the trunk!) and out to the drip line.