Yellow Wood Sorrel (Oxalis stricta), commonly called Oxalis or sour grass, is a vigorous weed. It is a summer annual -- sometimes perennial -- that thrives in fertile, warm and moist soils and likes shade.
The leaves, flowers and unripe fruits are edible, with a mild lemon-sour flavor - that's were it gets the name sour grass. Edible gardeners use it as a salad green or add them to soups, sauces or as a seasoning. It is rich in vitamin C and will quench thirst on hot summer days. Kind of nice to chew on when weeding.
Oxalis can easily be confused with clover when not in flower. It is differentiated by its small yellow flowers, heart-shaped leaflets, and lime-green to purple color.
A very common weed in lawns, green houses, landscape beds and container plants.
Creeping Woodsorrel has reddish foliage
Photo by Maja Dumat - flickr.com
Image courtesy of USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913.
Yellow wood sorrel has an interesting and effective way to spread seed. The pods build up pressure as they dry and then burst, sending the seed flying several feet. You can make the seed pods pop by lightly touching them.
Oxalis will take advantage of bare and thin areas in your lawn, quickly filling them in.
Hand Weeding - Hand weeding is very effective. It pulls easily and will not re-sprout from roots left behind. Removing the plants before they go to seed reduces the population.
Chemical Control - Pre-emergence herbicides are the most useful, they prevent seed germination - the way oxalis spreads.
Many post emergent herbicides are not effective. Timing and the use of a spreader/sticker are important. Yellow wood sorrel has a very waxy leaf and stem, water beads and rolls off. A spreader/sticker will break down the waxy layer, allowing the herbicide to penetrate into the leaf and then do its job.
Spot spraying young plants works well.
Stems - The stems are thin, sparsely hairy and able to root at the nodes.
Leaves -Leaves are a bright, light green to maroon color. They are compound with three heart-shaped leaflets and arranged alternately along the stem on long petioles.
Each leaflet is creased down the mid-rib. The leaves fold at this crease during the night and open in the morning. They also fold when under stress or in full sun.
Flowers - Tiny, bright yellow flowers with five petals that are 4 to 9 mm long. It starts blooming in mid-spring - producing flowers into the fall.
Roots - Long, slender rhizomes occur with a fibrous root system.
Clemson Cooperative Extension: http://www.clemson.edu/extension/hgic/pests/weeds/hgic2324.html
Virginia Tech Weed Identifiation Guide: http://www.ppws.vt.edu/scott/weed_id/trfre.htm
USDA Plants Database: http://plants.usda.gov