Weeds can be a problem in an organic garden and yellow wood sorrel weed is no exception. Also known as Oxalis stricta, yellow wood sorrel can be hard to tame because it grows year-round in milder climates. Yellow wood sorrel is related to a variety of other oxalis species, all of which can be problems in the garden and lawn. Related forms include redwood sorrel (Oxalis oregana), silver shamrock (Oxalis adenophylla), and ordinary wood sorrel (Oxalis corniculata). All of them can be managed in much the same way as yellow wood sorrel.
Yellow wood sorrel has foliage that resembles that of clover, except that the foliage usually looks as if it has been folded up the center of each leaf. The flowers of yellow wood sorrel are bright yellow, measure approximately 1/2 of an inch, and are made up of five petals. The plant forms thick clumps in the open ground such as lawns and flower beds.
The weed spreads both through horizontal stems and seeds that take root where it touches the soil. Both self-propagation methods are prolific. The seed pods hold about 10 to 50 seeds but can hold up to 5,000 seeds—giving it more opportunities to destroy gardens. Upon maturation, the pod distributes seeds as far away as 10 feet. They can even get stuck on garden tools, clothing, pets, and other wildlife. The seeds set from late summer through fall. The roots are complex and far-reaching and difficult to pull. Tugging at the stems of wood sorrel merely breaks the top portion away, leaving the root network to resprout.
How to Prevent Yellow Wood Sorrel Weed
An organic gardener must be diligent when trying to prevent or eliminate yellow wood sorrel weed. It is a difficult and time-consuming task, and in some cases, organic solutions may need to give way to discriminating use of chemical methods.
For an organic gardener, the key here is diligence—making sure that yellow wood sorrel is not allowed to set seed. The plants should be dug out or pulled as soon as you see them, getting as much of the root as possible.
Yellow wood sorrel weed thrives in open, fertile soil, which is why it can such a problem in lawns and garden beds, where the soil is so favorable to growth. To prevent wood sorrel from popping up in lawns, make sure that you maintain thick, healthy turf. Seed or sod any bare spots, because that is where wood sorrel weed will eventually pop up. Mulch garden beds with a two- to three-inch layer of organic mulch to prevent the weed from making a home amongst your perennials or vegetables. Without sunlight, the weed seeds cannot germinate.
How to Treat Lawns for Wood Sorrel Weed
If the wood sorrel weed is growing in cool-season turfgrass, such as bentgrass, Kentucky bluegrass, ryegrass, or tall fescue, treat the lawn with a post-emergent herbicide that contains the ingredient triclopyr. Be careful with herbicides because they may contain other ingredients. When you want to treat warm-season turfgrass such as St. Augustine grass, Buffalo grass or Bermuda grass, use a post-emergent herbicide containing the active ingredient fluroxypyr. Follow instructions carefully if you apply it to your lawn.
Treating Wood Sorrel in Garden Beds
In garden beds, the only organic approach is to carefully dig out the weeds, roots and all. This is a difficult task because the roots are tiny and the smallest piece left behind will resprout into new weeds. And you may need to dig up ornamental plants briefly in order to sift through the soil and remove the offending wood sorrel root. For many gardeners, the battle with wood sorrel is one they simply resign themselves to as an expected struggle.
Glyphosate (sold under brands such as Roundup) will kill the entire plant, roots and all, so it is the most effective chemical solution. Other narrow-spectrum weed killers don't touch wood sorrel.
This is a broad-spectrum plant killer that will kill all plants, so take great care to apply it carefully. Some gardeners brush the weed-killer by hand onto the leaves of the weed. If you spray, use a small spray bottle and apply the weed killer only to the weed foliage on a windless day when the spray will not drift onto other plants.
Uses for Yellow Wood Sorrel
Yellow wood sorrel is a nuisance for most gardeners, but it also has uses. All parts of yellow wood sorrel are edible, and they have a bright, tangy flavor. The leaves and blossoms can be added to a salad as a decorative touch, and a lemony drink can be made from the foliage.
Oxalis (Yellow Woodsorrel). University of Maryland Extension