Ideally, the mulch rings around trees should extend to the tree’s drip line. When landscape contractors plant trees properly, the mulched tree ring is usually just the right size immediately after installation. Problem is, the tree grows and in many cases the mulch ring doesn’t.
Trees that are surrounded by grass face stiff competition for water and nutrients. Mulch rings around trees help give them an edge by keeping the grass further away from the tree. As a tree gets bigger, it needs more water and more nutrients and therefore needs a bigger mulch ring to reduce that competition from turf.
Larger mulch rings also offer the advantage of making it easier to mow around trees and reduce the risk of damage to trees from mowing equipment.
Of course, it’s not always practical or even possible to expand the mulch ring all the way to the drip line. Commercial landscape contractors know that sidewalks, curbs, benches and other features of suburban outdoors spaces often get in the way. But expanding the ring even a little bit will be a big help to your tree.
This type of project can be done any time of year and is relatively easy. One way is to remove the grass with a spade and add mulch. This method provides an immediate and attractive result but is labor intensive and risks damaging the tree roots. An easier way is to carefully spray an non-selective herbicide like Roundup in the area in which you want to expand the mulch. Wait until the grass dies and cover it with mulch.
Roundup won’t work in the winter, but if you’re doing it that time of year just cut the grass as short as possible, cover it with mulch and spray Roundup when the grass starts to come back up in the spring.