Creeping woodsorrel is a common lawn weed.
Creeping woodsorrel is a member of the Oxalis family, which gets its name because of its sour taste. If livestock eat too much woodsorrel, they can get oxalate poisoning. Personally, I just don’t like seeing it in my lawn. It tends to grow in tandem with clumping tall fescue grasses, stealing nutrients, sunlight, and prime real estate from more desirable turf grasses and ground cover.
Know they enemy
Before you can eradicate creeping woodsorrel from your lawn, you need to understand how it lives, grows, and thrives. Creeping woodsorrel (Oxalis corniculata) is a perennial plant that grows close to the ground in all directions. This growth pattern is called prostrate (and don’t let me get started on what a pain in the rear getting rid of it can be!).
Creeping woodsorrel is often mistaken for a type of clover, with its three heart-shaped leaves. These are actually leaflets, and they can be green to purple, or even red. Sometimes the leaves fold downward. The plants have small, 5-petaled yellow flowers, which tells us that this plant is a dicot. The seed pods tend to stick up, are cylindrical with tiny hairs. Each seed pod can hold 10 to 50 seeds, which translates into each plant producing over 5,000 seeds! If I actually liked these plants (which I don’t), I would be really impressed by the fact that seeds are ejected from the pods, sometimes landing as much as 10 feet away. Also, the seed hulls are rough, making them stick to socks, tools, pets, lawnmowers, pretty much anything. Clearly, these plants need to be dealt with sooner rather than later.
Creeping woodsorrel seeds prefer temperatures between 60° and 80°F, but they grow year round in the Bay area. Temperatures over 97°F for 8 hours will halt this plant’s growth, but fall’s cooler weather is exactly what is needed for this plant to take over your lawn.
An ounce of prevention...
You should always check new, incoming plants for creeping woodsorrel infestation. Once it takes hold in your yard, you will have to be attentive year round. Hand weeding is the best control measure for creeping woodsorrel. New rhizomes are pink to bring red, making them easy to see. But if even one tiny bit of the root or stem is left behind, when you pull the plant from the ground, new plants will grow. This is one tough sucker to get rid of!
For severely infested areas, I have found that the best treatment is simply to dig it up. Each spadeful of soil is then crumbled by hand and every tiny bit of creeping woodsorrel is removed by hand. If this sounds like hard work, well, it is. At the same time, it is an amazing opportunity to see what is really going on underground! In the 3-foot by 4-foot space pictured, I came across 5 young grubs, what looked to be either cutworm or masked chafer pupa, and more earthworms than I’ve found on previous digs. I attribute to increased worm population to cooler temperatures, more frequent watering, and the addition of aged compost spread lightly on top of the lawn as food. I also found that the soil structure, while still compacted, is much better than it was three years ago. (These things take time…)
After breaking up the soil and fishing out the weeds, I mixed some aged compost into the pile and covered it with straw, leaving a bit of a trench around the edge (to prevent re-infestation). I will water the pile daily for a few days, just as I would with a new compost pile, to help break down the organic matter.
Next, I will use cardboard or some other temporary barrier to keep other plants from moving in and plant some oregano. If it works, great. If it doesn’t, I’ll have that much more organic material in the soil that will feed whatever grass seed I decide on. I have decided to combine ridding my yard of creeping woodsorrel with an experiment in unique ground cover/lawn replacement. I noticed that the oregano in my herb garden is delightfully low growing, soft to the touch, and it smells great when you step on it!
Be sure to check back and see how well it works!
UPDATE: One month has passed and the new grass is coming in very nicely, without any creeping woodsorrel. I do have some rouge curly lettuce (left) and the oregano planted on purpose (right), but the creeping woodsorrel is currently a minority in this patch of lawn!
I hope this information inspires you to grow more of your own food. You can ask your garden questions on my Home page.