Ditch Mulch Volcanoes And Try A Better Landscaping Alternative

Many people avoid using the mower and line trimmer around trees to avoid damaging their trunks, yet also don't want to spend their free time pulling weeds from around their bases by hand. In that case, adding mulch around the trees can seem like a logical way to solve the problem. It is an acceptable technique — with one exception. Mulch volcanoes, or mounds of mulch piled high around the trunks of trees, may keep weeds down, but they pose a risk to the tree itself, potentially causing a slow death. They interfere with the tree bark's protective qualities, create a barrier to hydration, and provide an entryway for pests and disease. A better alternative is to create soft landings at the base of trees with native plants. This protects the trees while providing habitat for native pollinators. 

Soft landings are particularly important to ensure a healthy ecosystem underneath keystone trees. Keystones are native plants that, over the course of millennia, have developed essential relationships with many types of native wildlife. They support insects throughout their life cycle, first by providing food, then by protecting them in their cocoons, and finally supporting the undergrowth, or soft landing, where the insects pupate. Oak trees, for instance, support more than 950 species of caterpillars. Other keystone trees include cherry, willow, pine, and poplar. Using native and pollinator-attracting ground covers as a living mulch underneath these trees promotes the survival of insects like butterflies, moths, beetles, and bumble bees, which are necessary for a diverse habitat.

The easiest way to begin creating soft landings under trees is to rake fallen leaves into the space around the trunk and under the tree's drip line — the area under the tree defined by the outer edges of the branches. The leaves will degrade, adding nutrients to the soil, preparing it for the introduction of plants that thrive when grown under trees. If there is already grass growing under the tree, smother it with newspaper or mulch topped with 2 inches of compost. Start 18 inches from the trunk and continue to the drip line. This is the space where you'll grow your soft landing.

The plants you choose to grow will depend on your USDA Hardiness Zone, how shady the area under the tree is, how moist it is, and how much time you can devote to maintenance. Native ferns are a good shady ground cover, while white wood aster (Eurybia divaricate) and green and gold (Chrysogonum virginianum) are drought-tolerant plants that thrive in partial shade. If your soft landing area is shady and damp, wild ginger (Asarum spp.) and sweet woodruff (Galium odorata) will do well.

If you prefer, you can continue to mulch your trees. Just don't create mulch volcanoes or let the mulch touch the tree's bark. There's no consensus on the best kind of mulch to use to combat weeds, but there is general guidance. Most organic mulches like wood chips, pine straw, and leaves should be spread 1 to 3 inches deep. Inorganic mulches like gravel or lava rock should be 1 inch deep. Keep the mulch 3 inches away from the trunk itself to prevent harm.