There are two types of Oxalis weeds found in Santa Clara
Note that while the Pest Note (linked above) mentions solarization as a possible control, the solarization pest note says that this method is best for plants which have roots in the upper six
inches of soil. Bermuda buttercup can often have roots or bulblets that
go deeper and therefore may not be killed. If you don't have a lot of
other plants in an area and can cover the area for at least four weeks during
very warm weather, it may be worth a try.
The pest note indicates that Bermuda buttercup is not usually a problem in lawns that are mowed regularly because repeated cutting of the plant eventually depleted the bulb. We have heard from some Master Gardeners
that after many years of pulling the weeds in a specific area, the
plants stop producing and are eventually eradicated. Persistence is the key. Keep pulling and digging those bulblets!
Mowing, fertilizing, or irrigating to
control creeping woodsorrel isn’t effective; the more vigorous the turfgrass,
the more vigorous the creeping woodsorrel. Creeping woodsorrel survives and
sets seed even when mowed as close as 1/4 inch. After using a lawn mower where
creeping woodsorrel grows, wash or air spray the machine to remove all seeds
and clippings before mowing weed-free turf.