Oxalis stricta (?) or common yellow oxalis annually invades my streetside
ground cover plants for about six months, from November through May, and
starves them of light, making for very spotty spring growth for the invaded
prostrate rosemary, red apple succulent, myoporum, and miniature ice plant
cover. They are persistent, nearly alien in their tenacity, and seem to
spread by seed, rhizome, and bulblets, so pulling does little good, even in
our soft loamy coastal soil in N. California. Since they die out from June
to October, letting them take over means barren ground in the summer months.
Is there any practical control solution outside of individually digging the
thousands of plants?
I would guess oxalis is in the clover family, but wouldn't clover control
chemicals also damage my four ground cover plants?
Thanks for any ideas!
"Roger" <sherry roger at comcast dot net> wrote in message
roger, I have that (or similar) in my lawn though the oxalis is a very small
leafed variety. Spraying it with a broadleaf spray knocks it back I have
noted in previous years. Check with a garden centre about the susceptibility
of your ground covers to the chemicals used. That is the cheap, nasty and
easy way of doing it.
Maybe a more enduring solution is to find a ground cover that grows well
over summer that can shade out much of the oxalis. Don't ask me what however
something that grows well late spring and dies back early autumn allowing
the other plants to take over. I have a succulent ground cover through some
of my gardens (the succulent essentially took over) that does well keeping
the weeds, including oxaslis, down. It does need a pruning every so often
and is a year round cover so not ideally what you want.
Oxalis does not spread by rhizome, only by seed. If the ground covers
were thicker, oxalis would be reduced. You could also consider adding
wood chips by hand in the ground cover. That will be a total pain but
it will give you a few years of respite.
Thanks for your advice -
I just got an ID from my local farm bureau, and my oxalis is "oxalis
pes-caprae". You can see it by doing a Google Image search for Bermuda
Buttercup. According to online sources, it reproduces primarily by bulbs
and less so by seed. Nevertheless, they give me little hope short of
using pre-emergent twice in the fall. I don't wish to follow the chemical
route, so I plan to replace my aptenia (red apple) , myoporum, and miniature
ice plant, with a more robust and competitive plant. So far, my prostrata
rosemary seems to to the trick and overcome the oxalis, especially when I
use landscape fabric for the small seedlings.
The long horizontal stems of oxalis will indeed take root if they touch
the soil. The plant really does not have bulbs, but the tops of the
taproots are swollen to a bulb-like appearance. The flowers form seed
pods that open explosively when touched, scattering the tiny seeds to
quite a disance. The seeds are sticky and will cling to your clothing,
dropping off later to scatter the plants even farther.
There are spray-on herbicides that are specific to oxalis and also
spotted spurge, containing ammonium thiosulfate. Oxalis and spurge are
severely burned by this spray. If the foliage is completely wetted by
the spray (add liquid soap to promote wetting), it will kill growing
oxalis and spurge plants. Unfortunately, the seeds are not affected; so
frequent respraying might be necessary.
The spray will not harm most other plants, but carefully check the
label. Also ask at your local nursery (providing they have an herbicide
expert on staff). I think it will damage junipers and some varieties of
iceplant, but they should recover if not thoroughly wetted.
After a very few days, the herbicide decomposes. A by-product of
decomposition is nitrate nutrients for other plants.
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