Native Plants

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Wednesday - November 26, 2014

From: Austin, TX
Region: Southwest
Topic: Planting, Erosion Control, Groundcovers, Shade Tolerant, Grasses or Grass-like
Title: O.K. to grow grass under a live oak?
Answered by: Guy Thompson

QUESTION:

Is it a bad idea to plant grass around a mature live oak? We have erosion issues and trying to keep mulch in the beds around the tree groves is a challenge, even with edging. Much of the native dirt has actually washed away over the past several years when we gave up on mulch and some of the roots are starting to become exposed. A landscaper has suggested putting grass up to the trees to help with erosion. Honestly, I wouldn't mind if the tree growth slowed, but I do want them to stay healthy and disease free.

ANSWER:

Before planting anything you will need to confront the erosion problem that you have. Perhaps you could build swales or barriers to redirect rainwater away from the oak until your new plantings take hold in some freshly added soil.

Growing grass under a live oak will not harm the tree. The problem is finding a grass that will thrive in the tree's shade. Hopefully you have a high canopy that allows considerable light to reach the ground. There are no native turf grasses that do well in shade. However, there are several bunch grasses that would look nice under light shade. These grow too tall to stand foot traffic, but they can be quite attractive.

One grass that I grow in shade as a ground cover is Paspalum setaceum (Thin paspalum). It grows only a few inches high and the rather unattractive foot-tall seed heads can be controlled by mowing. If you can accept taller species, consider the following suggestions, taken from a previous Mr. Smarty Plants answer:

Bouteloua curtipendula (sideoats grama), the State Grass of Texas, 2-3 feet

Bouteloua hirsuta (hairy grama), 10-18 inches

Chasmanthium latifolium (Inland sea oats), 2-4 feet, a particularly attractive plant that grows well in deep shade

Elymus canadensis (Canada wildrye), 2-4 feet

Poa arachnifera (Texas bluegrass), 2-3 feet

Schizachyrium scoparium (little bluestem), 2-4 feet

You might also consider using sedges. They make very good groundcovers and they tend to be rather short. You can read about their use for lawns in Sedge Lawns for Every Landscape by John Greenlee.

Carex blanda (eastern woodland sedge), 1-3 feet

Carex cherokeensis (Cherokee sedge), 12-18 inches

Carex planostachys (cedar sedge), less than 12 inches

Carex texensis (Texas sedge), 10-12 inches

Finally, here are a few groundcovers that aren't grasses or grass-like, are less than 18 inches high and will grow in the shade or part shade. They are mowable. I attach extra images of these.

Calyptocarpus vialis (Straggler daisy)

Ruellia humilis (Fringeleaf wild petunia)

Viola affinis (Sand violet)

Seeds for many of these plants may be obtained at your local plant nurseries. Native American Seed is a particularly good source.

From the Image Gallery

Horseherb
Calyptocarpus vialis

Prairie petunia
Ruellia humilis

Sand violet
Viola affinis