Yellow Woodsorrel (Oxalis stricta)
Yellow woodsorrel, also commonly called oxalis, is a perennial weed that grows throughout the year. It is often confused with clover; both have trifoliate leaves. Oxalis flowers have five petals, and the leaves are divided into three partly-folded, heart-shaped lobes.
It spreads by thin rhizomes underground and by seed. The plant flowers in the spring and into early summer. A single plant can produce 5000 seeds, has close to 100% germination rate, and the seed capsules explode open, sending seeds up to 16 feet away. The plant also has the ability to keep producing seed after it has been pulled out of the ground, so make sure to dispose of it. Its seed can survive very hot temperatures, so do not add this weed to your compost piles.
Good cultural practices are vital to keeping yellow woodsorrel from invading your landscape. The weed is problematic in the nursery trade. Always inspect and remove weeds from plants before bringing them home. If the plant does have oxalis in the container, remove some of the potting media before planting since the weed can regrow from rhizomes and root fragments.
Yellow woodsorrel seeds need light to germinate. Keep a three-inch layer of mulch in landscape beds to minimize the growth of seedlings. Hand-pull weeds when they are small to limit underground spread. If oxalis is a problem in your lawn, take steps to improve the density of the grass. Make sure to mow your lawn at the proper height. For more information on proper mowing height, fertilization, irrigation, and aeration, see HGIC 1205, Mowing Lawns , HGIC 1201, Fertilizing Lawns, HGIC 1207, Watering Lawns, and HGIC 1200, Aerating Lawns.
Pre and post-emergent herbicides can also be used to provide control of yellow woodsorrel. For recommendations, please see HGIC 2329, Oxalis Control.