How can I get rid of grass under a swamp willow?

Asked September 24, 2015, 9:00 AM EDT

Our large swamp willow has large surface roots. We have a combo of weeds and grass that grow up and between. We want to cover the whole with mulch to look good and get rid of the weeds/grass there. How can we do that safely without damage to the tree or our well water?

New Castle County Delaware

1 Response

Willow trees naturally grow in high water table soils and therefore, have developed a root system that does not extend deep into the soil. As the tree matures, the upper roots remain near the soil surface and extend outward away from the main trunk. This root structure not only supports stabilizing roots, but also the small 'feeder' roots. The larger the tree, the more surface roots you will find penetrating through the upper soil layer. This is also true for other 'Bottomland hardwood' species such as: Silver maple and alder.

Roots develop a thin protective outer-bark around them - which can easily be damaged by lawnmowers and other lawn care equipment. Damage to the exposed roots cause 'cankers' and serve to vector disease and insect into the tree's entire system.

Since the roots occur near the soil surface, any application of mulch or soil as a covering will prohibit necessary oxygen exchange between the air surface and the root tissue - essentially suffocating the root. If you plan to apply mulch, make sure it is of an organic material and light-weight. Only applied a few inches deep - to allow air to flow easily to the root system and throughout the surround soil surface ... where gravity will pull down water into the aquifer to recharge your well. If you treat the unwanted grass around these exposed roots with an herbicide, be aware any open areas or 'cankers' can vector the chemical into the entire vascular system. Apply herbicides according to label directions. ~DOT