February 18, 2017

1 – Oxalis plants may look like clover, but they are a different plant that can become problems in landscapes and gardens.

Yard and Garden February 18, 2017

Q.

I inadvertently brought home a clover seedling in a plant for the garden store. Over the last two years it has moved quickly throughout our lawn. We have used different herbicides many times and only managed to kill the grass. The clover has both a green leaf with a yellow flower and a dark pinkish purple leaf type. I am concerned that it will totally choke out the grass if left alone. What can we do to get rid of this clover?

- Clarissa J.

A.

The invasive plant you are describing is not clover, it is a plant known as wood sorrel. This plant is in the genus Oxalis, a genus which includes about 800 species of interesting plants. Some of the species of Oxalis are attractive and used as ornaments, others produce edible tubers, and others, such as the one you brought home, are invasive weeds. This weed often comes in with plants in containers from the nursery or transplants from a friend’s garden. All oxalis plants contain oxalic acid, which explains the name Oxalis. The oxalic acid gives these plants a sour taste when chewed. Although oxalic acid can be toxic in large quantities, health people are unlikely to eat enough to cause problems. Many other edible plants, such as broccoli and spinach, also contain oxalic acid.

The invasive forms of Oxalis may spread underground by means of rhizomes or may produce numerous small tubers underground. Both of these structures may explain why you are having difficulty controlling it even with herbicides. The rhizomes and tubers may survive initial chemical treatments. Some herbicides may provide control of Oxalis if used properly and persistently, but the use of the wrong herbicide in the wrong location can result in death of lawn grasses and garden plants. Your local NMSU County Extension Service agent can help you determine the best herbicide to use in your location and with your specific lawn grass. A healthy, thick lawn will often greatly reduce growth of oxalis weeds, but thin areas of lawn and perimeter areas that receive extra sunlight will often allow the weeds to grow.

Digging oxalis weeds by hand to remove the roots and rhizomes below ground is a good way to eliminate oxalis, but failure to remove all the underground rhizomes or hoeing to just chop the plants will result in failure. Thick mulch in gardens and non-vegetated areas can also greatly reduce oxalis.

Timing is important when managing oxalis because the plants rapidly produce numerous seeds after flowering. If seeds are allowed to form, the weed problem will persist and spread. To complicate the issue, oxalis seeds “explode” from the seed capsules of some species when the seeds ripen. This scatters the seeds over a large area, hastening the spread of the problem and increasing the difficulty of managing this weed. Your goal should be to prevent seed production in addition to removing any underground portions of the plant. Combination of physical removal, mulch, and appropriate use of herbicides may be the best way to stop the spread of this weed in your lawn. However, it will probably not be accomplished quickly. Persistence is the best herbicide!

For more gardening information, visit the NMSU Extension publications Web site at http://aces.nmsu.edu/pubs/_h, or to read past articles of Yard and Garden go to http://aces.nmsu.edu/pubs/periodicals.html.

Send your gardening questions to Yard and Garden, Attn: Dr. Curtis Smith at cwsmith@nmsu.edu or leave a message at https://www.facebook.com/NMSUExtExpStnPubs.

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist, retired from New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.