Mulch: how much, and how often

Mulch keeps moisture in the soil, slows down weeds and gives beds a finished look. It is easy to overdo, though, and too much mulch causes its own problems.

How deep

Two to three inches is the usual target. Less than that and weeds come through. Much more and water has trouble reaching the soil, and roots can start growing up into the mulch instead of down.

Keep it off the stems

Mulch piled against tree trunks and shrub stems holds moisture against the bark, which invites rot and pests. Leave a few inches of space around each stem. You may hear this called avoiding “mulch volcanoes.”

How often

• Check the depth each spring and top up only where it has thinned out.
• Fluff old mulch with a rake if it has formed a crust that sheds water.
• Most beds need a fresh layer every year or two, not every season.

Shredded hardwood and bark are good all-round choices. If you have a lot of trees, shredded leaves from the fall cleanup make a free mulch too.