Invasive humans (and their flora)

At a party in the San Lorenzo Valley town of Felton last night, I found myself chatting in a pleasant and typically Californian group of three - a Scot, a German, and a Frenchwoman.

We non-native Californians are all over the place. Unfortunately so are the plants we have introduced. My main battle at the moment is against the omnipresent South African import, Oxalis pes-caprae. (Pes caprae means goat's foot in Latin, I think.) It's not in flower right now so I grabbed a picture from the internet.
(Photo by Jonathan Alcorn, accessed 12/22/08 here:

You'll recognize it I know, by its pretty yellow flower and clover-like leaves, though you may be more familiar with it as "sour grass" if you have children who like to suck on the flower stems. (Oxalis is poisonous but not in such small doses.)

I have been slacking off lately and the pes-caprae troops have received massive reinforcements. I want to root them out before they stock up on cannon balls -- I mean the little root nodules that remain in the ground when you pull them, making this Oxalis so hard to get rid of. My friend, the naturalist Jeffrey Caldwell, told me that gophers gather the nodules and store them for eating, which helps the weed to spread. I also believe they reseed freely. I've tried Roundup I confess in hard-to-treat areas and it is successful but only if you keep on squirting. I feel guilty every time I spray. Hand pulling is more effective, but again, only if you repeat repeat repeat. I'm seeing headway in the areas where I have been most diligent. But not victory. It's time for a Churchillian speech to keep up the spirits.

Or a new secret weapon.

I was cheered in this regard when I met Cameron Colson recently, an energetic young businessperson with a new application for power washing technology: invasive weed control.

We happen to have a power washer, and I'm going to give it a go on my own. Cameron has industrial strength machinery but the only specialized part is a special nozzle. He can take down trees! But I just want to see what it does to the Oxalis pes-caprae. The technique promises to turn all surface vegetation into a nice mulch, and, with three applications to blast away the regrowth, to significantly reduce the weeds. It's not only chemical free, but improves the health of the soil.

I'll write about my experience, and about Cameron's ideas and fledgling business, in another post.


Town Mouse said…
That should be very interesting indeed. I must admit to going out very early before the neighbors are awake with some RoundUp and an eye dropper to do some "touch-up" on my newly remodeled front garden. Some of the previous plants are impossible to pull, and the RoundUp seems to do the trick. Nasty stuff, though. I use very little, mostly I pull.
I can't imagine going over the area, which is mulched to 3-4 inches, with a power washer...
Anonymous said…
Do you think that you may have awakened and scattered the bubils of the oxalis? Those little buggers seem to get away so easily and grow up to be more oxalis!!!

Steven C. East Bay hills
Country Mouse said…
It's true they spread by root nodules - you have to weed before they develop. I didn't see any on some test areas, and I can only hope for the best. Once the nodules develop the best you can hope to do stop them flowering and setting seeds and try again next year.
Linda said…
ah, sour grass is the oxalis being discussed on the idora blog site. it seems i have fully under-appreciated not having it appear on my property. have you ever thought of sheeting over it with sections of newspaper or bags from the bulk section of your local grocers and then topping it off with wood chips. given that they are bulbs would they last more than a season or two deprived of growing rights? ls