Yellow wood sorrel (Oxalis stricta) is an invasive species in Kentucky and is considered a weed throughout the rest of the U.S. It looks similar to clover, except that the foliage is curved or folded at the center of each leaf. The leaves fold at night and open again during the day. Its small 1/2-inch five-petalled flowers are bright yellow. It can be hard to tame because it grows year-round in milder climates and many habitats. The plants should be dug out or pulled as soon as you see them, getting as much of the root as possible. It's native to North America and Eurasia. It is considered toxic if ingested by foraging livestock, particularly in Australia , and is listed by the ASPCA as being toxic to cats and dogs.
|Common Names||Yellow woodsorrel, common yellow oxalis, upright yellow-sorrel, lemon clover, sourgrass, sheep weed|
|Botanical Name||Oxalis stricta|
|Mature Size||10 to 20 inches tall|
|Bloom Time||Mid-spring through fall|
|Hardiness Zones||5-11, USDA|
|Native Area||North America, Europe, Asia|
|Toxicity||Cats, dogs, livestock|
Yellow Wood Sorrel Invasiveness
Yellow wood sorrel is reported as invasive in Kentucky by the Kentucky Exotic Pest Plant Council. You can find it throughout most of the U.S., where it is considered a prolific weed.
Yellow wood sorrel grows in USDA zones 5 through 11 in different environments, such as open woods, prairies, stream banks, gardens, and poor soils. It is reported in all the contiguous United States, except Oregon, California, Nevada, and Utah, but likely occurs in those states. It is also reported from Newfoundland and Labrador west to Manitoba and British Columbia.
This weed spreads through horizontal stems (runners) 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 them more opportunities to overtake gardens. The pod can distribute its seeds as far as 10 feet upon maturation. Seeds also get stuck on garden tools, clothing, pets, and other wildlife, transferring to other areas. The seeds set from late summer through fall. The roots are complex, far-reaching, and challenging to pull. Tugging at the stems of wood sorrel breaks the top portion away, leaving the root network and giving it a chance to resprout.
Since it can become invasive or weedy in your garden, you might want to consider growing it as an indoor plant instead. It can grow well indoors in containers. If you plant it outdoors, consider growing it in a container to reduce its runners from overtaking your yard. Also, deadhead the flowers as soon as they fade and remove any forming seeds pods. A mature seed pod can burst with touch, so carefully pluck it to control the spread of its seeds.
What Does Yellow Wood Sorrel Look Like?
Like clover, the leaves radiate from a single point like fingers from a palm in threes. The stems, branches, and leaf stalks have fine hairs on them. The plant forms in thick clumps.
Sorrel has a bright green color, and small yellow five-petaled flowers bloom from mid-spring to fall. The flower is about 1/2 inch in diameter. The plant doesn't usually grow taller than 20 inches. The plant produces small, green seed pods that look like okra; they're about 1/2 to 3/4 inches long.
How to Get Rid of Yellow Wood Sorrel?
Yellow wood sorrel often plagues lawns and garden beds. There are two ways to get rid of it—physically and chemically.
For many gardeners, the battle with wood sorrel is an expected struggle. In garden beds, the only organic approach is to dig out the weeds—roots and all—carefully. This task can be difficult because the roots are tiny, and the smallest piece left behind will resprout into new weeds. You might even need to dig up nearby plants to sift through the soil and remove the offending wood sorrel root.
Glyphosate (sold under the brand name Roundup) will kill the entire plant, roots, and all; it is the most effective chemical solution. Other narrow-spectrum weed killers won't affect wood sorrel.
Glyphosate is a broad-spectrum plant killer that will kill all plants, so carefully apply it. 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.
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 have other ingredients. When treating weeds in 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.
How to Prevent Yellow Wood Sorrel Weed
An organic gardener must be diligent when preventing or eliminating the yellow wood sorrel weed. It is a time-consuming and challenging task, and in some cases, organic solutions may need to give way to discriminating use of chemical methods.
If going the herbicide route, post-emergent herbicides will work best on this plant. Late spring is the best time to apply when emerging weeds are small and actively growing. It is much easier to kill small weeds. Actively growing weeds are more likely to take the herbicide and move it through the entire weed down to its roots. You can use post-emergent herbicides during the summer. Still, it may take several applications to control the weeds you target (only use in temperatures less than 85 F). They will also work in the fall when weeds are preparing for winter.
For the organic gardener, the key here is diligence. Do not allow yellow wood sorrel to set seed. The plants should be dug out or pulled as soon as you see them. Get as much of the root as possible. It can be difficult and time-consuming, but you can root it out by inspecting your lawn and garden beds daily.
Yellow wood sorrel weed thrives in open, fertile soil, which can be a problem in lawns and garden beds, where the soil is favorable to growth. To prevent wood sorrel from popping up in yards, ensure that you maintain thick, healthy turf. Seed or sod any bare spots because that is where wood sorrel weed will find an opportunity to grow. 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.
None of these methods are permanent since seeds can travel on the wind from other yards or via birds and other animals.
How to Tell the Difference Between Yellow Wood Sorrel and Red and White Clover
Yellow wood sorrel is easily mistaken for red or white clover, although sorrel has heart-shaped leaves and red and white clover leaves are oval-shaped. Also, as the name implies, the flowers of the white clover are white, and red clover flowers are more like a deep pink color.
Wood sorrel is also often confused with shamrocks—another plant in the clover family. Sorrel is sometimes called "false shamrock," and during St. Patrick's Day season, it's common to find yellow wood sorrel misbranded and sold as shamrock.
Another plant commonly mistaken for yellow wood sorrel is black medic, a similar-looking plant with small yellow flowers that is a cool-season summer annual.
Is yellow wood sorrel an invasive plant?
In short, yes, it is listed on the "moderate threat" invasive plant list in Kentucky. To be classified as an invasive species, the plant must be "non-native and able to establish on many sites, grow quickly, and spread to the point of disrupting plant communities or ecosystems." Technically, the plant is considered native to the U.S., but it may not be native initially to Kentucky. It is classified as a herbaceous weed everywhere else.
Can you eat 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 it has 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. However, it contains oxalic acid, which is considered toxic to cats, dogs, and livestock.
How do you get rid of yellow wood sorrel without killing grass?
Oxalis can be removed by hand or dug up using a hoe or spade. You can also use a chemical weed killer. You can get commercial herbicides that kill weeds and feed your grass simultaneously. To keep it away, feed your lawn, mow high, and water deeply to give your grass the best chance at beating back aggressive growers like Oxalis stricta.
Yellow wood sorrel. Missouri Department of Conservation.
Guide to poisonous plants. College of Veterinary Medicine and Biomedical Sciences. Colorado State University.
Yellow woodsorrel: oxalis stricta (Geraniales: oxalidaceae): Invasive Plant Atlas of the United States.
U.S. Forest Service. Common yellow wood sorrel. USDA.