In Praise (and Otherwise) of Oxalis

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In an uncertain world, there’s one thing you can count on in Berkeley every late winter and spring: Oxalis pes-caprae, also known around town as oxalis, Bermuda buttercup, yellow wood sorrel, “some kind of shamrock,” and sourgrass. “Sourgrass” because the stems are edible and tart, and both our kids, as well as lots of their friends, occasionally picked the grass and ate it when they were little.

On one hand, the plant is not unattractive–the blooms are almost iridescent in the right light–and was once something that gardeners planted ornamentally. I have a neighbor who says he likes to let the plant have its day, seeing how pretty it is for a few weeks every year.

On the other hand, the damned thing’s a nuisance. It’s ubiquitous, showing up in garden beds far and wide. Once it arrives, it’s virtually to get rid of. Pulling it up, you discover it has little white translucent tubers that seem to have something to do with how it spreads. You also occasionally find miniature bulbs from which the plant grows in the fall. Since it’s an alien (it’s native to South Africa) and invasive, it’s more than a headache for gardeners. Here’s what the University of California’s Integrated Pest Management site says about Oxalis pes-caprae:

Bermuda buttercup was first noted in California in the San Francisco Bay region and has since spread throughout most coastal counties, the coastal range, and into the Central Valley. In the last 10 years, this plant has invaded native coastal dunes and natural areas along the coast, leading to the demise of native plants. It is a troublesome weed that is more competitive than is assumed from its general appearance.

Due to its extensive occurrence in yards and gardens, Bermuda buttercup has the potential to rapidly spread via the production of bulbs and the movement of contaminated soils into adjacent natural areas. Because it is practically impossible to eradicate infested soils of this weed, take care to prevent Bermuda buttercup from invading wild lands.

And here’s what the site says you’re in for if you’re really dedicated to the cause of eradicating your personal patch of oxalis:

The best control method for this pernicious weed is prevention. If new infestations are spotted and controlled early, it is possible to eradicate small populations. Large populations are difficult to control and will require multiple years of diligent control efforts.

Small infestations can be controlled by repeated manual removal of the entire plant. Repeated pulling of the tops will deplete the bulb’s carbohydrate reserves, but these efforts will take years to be successful. Repeated mowing also will eventually deplete the bulb. Cut Bermuda buttercup before it flowers and forms new bulbs. Repeated cutting or cultivation is necessary to reduce plant numbers. The soil from which plants are removed should be carefully examined or sifted to remove bulbs and bulblets, an extremely time- and labor-intensive process. Before planting in an infested area, use soil solarization to further reduce Bermuda buttercup populations.

Soil solarization? Here’s the details on what that means.

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