March 19, 2011 Oxalis: From Ornament to Nuisance Originally published in the Contra Costa Times by Chantal Guillemin, UC Master Gardener Oxalis pes-caprae, or Bermuda buttercup, has

become a serious nuisance plant in gardens.

SUMMARY Q: How can I get rid of oxalis in my yard? tenacious, prolific weed which has I pull it out and think I’ve got it all, but it devised many successful survival Originally imported from just comes back with more gusto the strategies. Each year, after the first South Africa as an following year. It’s annoying, to say the seasonal rains, and sometimes before in ornamental plant, least! a dry year, about a dozen ovoid bulbils Bermuda buttercup develop along the length of the (Oxalis pes-caprae) has A: From November through April, the threadlike, underground rhizome. These become a tenacious and bright yellow flowers of Bermuda readily detach from the rhizome to frustrating weed buttercup, Oxalis pes-caprae, also known replenish the soil seed bank. Another throughout California. as buttercup oxalis, cape sorrel or survival technique of Bermuda buttercup Control requires equal sourgrass, cluster on the ends of slender is that, after initial removal by hand, tenacity of the gardener. leafless stalks. It can be seen throughout new plants will grow from broken off Understanding its life Contra Costa County in the compacted, stem segments left in the soil. Several cycle and growth poorly-drained clay soils of yards, passes at hand weeding may be characteristics is key. gardens, turf, landscaped areas, urban necessary to completely remove this new places, orchards, vineyards, fields and growth. Discouraging survival of among agricultural crops. A native of Bermuda buttercup can be accomplished South Africa, it is found throughout by gently pulling on the plant and California up to 8200 feet (2500 m). removing all of it just as it is about to Though sometimes used as a rock flower. By this time, the parent bulb garden ornamental, it’s generally viewed energy reserves are exhausted. The as a chronic nuisance because of the parent bulb should be completely dried difficulty in curbing its ability to spread out and most young bulbils too within flower beds, groundcovers and immature to survive disturbance. shrub plantings. Prevention Is Ideal: Tenacious & Prolific: Bermuda buttercup can establish a Homeowners and gardeners wishing to foothold in a variety of ways. Gardeners eradicate Bermuda buttercup face a

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aid in the dispersal of bulbils when they controlling Bermuda buttercup suggest move soil from an infested area to one covering it with stiff cardboard and “Though complete that is free of the weed. This happens applying a thick layer of mulch. The through cultivation, intentional planting goal is to weaken the bulbs and deprive eradication is all but and recycling of garden waste and the plant of sunlight, causing an inability nursery soil. to photosynthesize and eventual death impossible to achieve, by starvation. Chemical control can Unsuspecting gardeners may introduce affect the top growth but is ineffective in following strict non- soil harboring Bermuda buttercup plants preventing bulb germination. from nursery-bought containers. contamination Difficult to see Bermuda buttercup The lack of movement of water and air bulbils found on hand-pulled rhizomes between compacted clay soil molecules practices, mulching, and in contaminated soil are not killed promotes the survival of Bermuda by the high temperatures in the compost buttercup bulbils. Adding nitrogen-rich solarizing, improving pile. Prevention dictates the removal of organic matter will loosen existing soil contaminated soil and hand weeded particles and benefit soil structure by soil structure and Bermuda buttercup from garden increasing porosity and improving premises. Also, voles who consider drainage. drainage are all steps Bermuda buttercup a palatable food source can aid in the spread of bulbs Though complete eradication is all but gardeners can take to from the source population. impossible to achieve, following strict non-contamination practices, mulching, create an environment Controls: solarizing, improving soil structure and Though prevention is the best control drainage are all steps gardeners can take unfavorable to the method, soil solarization can reduce the to create an environment unfavorable to bulb population. To be effective, the establishment and survival of establishment and solarization using a clear plastic tarp Bermuda buttercup. treated with an ultraviolet light inhibitor survival of Bermuda must be in place for no less than 4 For More Information: consecutive weeks during June, July, or For more information, see UC’s free Pest buttercup.” August. The sun’s rays will heat up the Note entitled Creeping Woodsorrel & soil to temperatures that are lethal to Bermuda Buttercup, available at: Bermuda buttercup bulbs. Some http://ipm.ucanr.edu/PMG/PESTNOTES/pn researchers investigating approaches for 7444.html

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