Oxalis: Dr. Jekyll or Mr. Hyde?

When I was growing up it was fun to pick a weed we called Sheep Sour and enjoy its slightly sour taste. I have since learned that this is the oxalis plant that frequently infests our yards. In researching information for this article, I found that oxalis (wood-sorrel) has been consumed by humans around the world for millennia. Dr. James Duke indicates in his book, Handbook of Edible Weeds, that Native Americans consumed it in several ways. The Kiowa chewed it to alleviate thirst on long trips, the Potawatomi cooked it with sugar for a dessert, the Algonquin considered it an aphrodisiac, the Cherokee ate it to alleviate mouth sores and sore throat and the Iroquois ate it to help with cramps, fever and nausea. Varieties that produce large tubers are cultivated and sold in South America and New Zealand for food.

The sour taste is derived from the oxalic acid present in all parts of the plant. It shares this oxalic acid- containing property with other foods such as spinach, broccoli, Brussels sprouts, grapefruit, chives and rhubarb. Oxalic is considered to be toxic in large amounts, but the U.S. National Institutes of Health consider this toxicity in foods to be of little consequence for people who eat a variety of foods and in moderation. The presence of high levels of vitamin C led to its being called scurvy-grass and being eaten by sailors to prevent scurvy.

Yellow wood-sorrel (Oxalis corniculata var. dillenii) is the yellow-flowered perennial weed found in lawns. It is a low growing plant that is native to all the lower 48 states but is not common in the panhandle and far west of Texas. It is not particular about the type of soil in which it grows but does not tolerate poor drainage. Too much moisture results in the bulbs rotting. It blooms from May through November. This plant tends to spread and can be difficult to control since it can spread by seeds and stems. Hand digging may take several seasons to accomplish control. Do not try pulling the plants up because they have extensive root systems and a tiny piece of root left in the ground will regrow.

Broadleaf herbicides may be effective but often require multiple sprayings. Be sure to read labels and follow instructions carefully. It has been suggested that a more nearly organic approach is to try liquid chelated iron.

Other varieties of oxalis are available in the spring in the garden centers as either bulbs or plants. These ornamental varieties are not cold tolerant and must be brought indoors in the winter or treated as annuals. These ornamental varieties are grown both for their flowers which range in color from whites and yellows to bright pinks. There are double flowered and multicolored varieties also. The foliage can be found in light green with darker areas near the stem (similar to zonal geranium leaves), speckled and dark purple (Oxalis triangularis). All of these varieties are adaptable to outdoor growth as well as to growth in containers. The planting area outdoors should be well-draining and provide for adequate sun exposure. Several hours of sun with some afternoon protection is desirable. Coffee grounds spread around the plants will help provide a slightly acidic soil. These plants will grow in shady areas but the general rule is that less sun will result in fewer flowers. The darker leaved varieties require more sun than the light green ones; however, too much sun will cause the leaves to “bleach out.” Planting the bulbs only requires that a small hole be made in the soil 1” – 1 ½” deep and 3” to 4” apart. Container planting follows the same guidelines. Oxalis regelli is recommended for container growing. The container should be filled with a good potting soil, and it should possess drainage holes in the bottom.

Up to six plants can be placed in an 8-inch pot, 10 plants in a 10-inch pot and up to 15 plants in a 12-inch pot. These plants will show foliage in a few weeks and produce flowers in six to eight weeks. The ornamental flowers are larger than the ones on the weeds.

Whether you are battling “Mr. Hyde” in your yard or cultivating “Dr. Jekyll” in your flower beds and pots, you are experiencing the two sides of oxalis.