A Question of the Week

young oak leaves

Q. We can’t seem to get grass growing under the oak tree in our yard. Any suggestions?

A. Trees add beauty, grace and shade to a home landscape, but most grasses thrive best in full sun. Less light means less photosynthesis, which means less carbohydrate synthesis and less food for the grass plants. Also, under the leaf canopy of a large tree, grass has to compete with the tree roots for water and soil nutrients.

These tips may help you establish a carpet of grass under your tree:

  • Choose a shade-tolerant grass-seed mix. Species that do well in full sun don’t do well in shady locations.
  • Carefully prune the lower branches of your tree to a height of six feet.
  • Avoid applying excessive nitrogen fertilizer in shady areas. Fertilize sparingly in fall as the leaves begin to drop or in early spring before the tree leafs out.
  • Set your mower blades high and keep the grass relatively tall (about three inches). The longer grass blades intercept more light for more photosynthesis.
  • Water the grass under the tree only enough to prevent the topsoil from drying out. Water in the morning, as late-day irrigation may promote disease.
  • Rake the leaf litter from under the tree each fall.

If these practices fail to give you the desired results, consider planting a shade-tolerant, low-maintenance ground cover. Or you could maintain a 2” to 4” layer of bark mulch that extends out to the tree’s dripline (edge of the leaf canopy above). Don’t allow the mulch to touch the trunk of the tree, and certainly don’t pile a cone of mulch up around it. These “mulch volcanoes” may harbor mice, insects, and disease organisms that could harm your tree.

originally published May 10, 2013