In winter, snow is seldom seen in the mild Mediterranean-climate areas of California. Instead, many of our gardens sport blankets of green clover-like foliage of the bulb known to botanists as Oxalis pes-caprae. Also called Sourgrass, Cape Sorrel or Bermuda Buttercup, this yellow-flowered pest is endangered in its native South Africa, where many natural predators keep it in check. Californians, alas, are not so lucky. Even well-established planting beds can be overrun or smothered by this greedy “imperialist” of a vegetable, which spreads by both rhizomes and bulbs. How to mount an offense against the offensive Sourgrass? Try some or all of the following approaches to kill the plant’s foliage, thereby starving and eventually eliminating the bulbs.

Weed, Hoe and Mow: Daintily remove individual plants by pulling them up by their main stems. Alternatively, hoe or mow down all foliage. Gardeners with acreage to reclaim might look into hiring goats.

Chemical Weapons of Mass Destruction: RoundUp (glyphosate) is one of the least environmentally nasty of the “better-living-through-chemistry” herbicides. For maximum effectiveness it needs to be sprayed on a still, dry day when temperatures are above 60 degrees F. (Not so easy during winter.) Spray the foliage, being very careful to avoid plants that you do not want to kill. Wait two weeks for the next dry, still, warm day, and spray again. If you’re lucky you will not have to repeat this procedure for more than a couple of winters.

Because Sourgrass reproduces by bulblets produced along the main root of the plant in late winter, DO NOT TILL an infested area unless you wish to spread the bulbs around and provide yourself with a lifetime hobby. Also, while the jury is still out on whether Sourgrass produces viable seed in California, there’s no sense in waiting for the verdict: chop off those pretty yellow flowerheads as soon as they appear.

–Margaret