Yellow woodsorrel, a perennial weed, is usually first noticed when it forms yellow flowers from May through September. The stems are green to purple, erect, branching from the base with alternate leaves that have long petioles. Leaves are clover-like with 3 heart-shaped leaflets. Trifoliate leaf arrangement similar to white clover or black medic (which it is often mistaken for) but leaflets are distinctly heart-shaped; The yellow flowers are borne on long stalks arising from the leaf axils. The seeds are formed in erect capsules that when ripe explosively eject seeds as far away as 12 feet. The root system is shallow and fibrous along the length of long slender white to pink rhizomes.
Creeping woodsorrel (Oxalis) is more prostrate, frequently roots at the nodes and often has leaves with a purple tint, unlike Oxalis stricta.
Conditions that favor growth
Yellow woodsorrel thrives in moist fertile soils but grows under a wide range of conditions.
Management in lawns
Maintain healthy, dense turf that can compete and prevent weed establishment.
Hand pulling or using an appropriate weeding tool are the primary means of mechanical weed control in lawns. This is a viable option at the beginning of an infestation and on young weeds. Hand pulling when the soil is moist makes the task easier. Weeds with tap roots like dandelions or have a basal rosette (leaves clustered close to the ground) like plantain are easier to pull than weeds such as Bermudagrass (wiregrass) or creeping Charlie (ground ivy) that spread with stolons or creeping stems that root along the ground.
Chemical treatment in lawns
Herbicides should be used as a last resort because of the potential risks to people, animals, and the environment. Be aware of these lawn herbicide precautions first.
If you chose this option, spot treat weeds with a liquid, selective, postemergent, broadleaf weed killer applied when weeds are actively growing. Look for a product with one or more of the following active ingredients:
2, 4-D, MCPP (mecoprop), Dicamba* or Triclopyr.
*Do not spray herbicides containing dicamba over the root zone of trees and shrubs. Roots can absorb the product possibly causing plant damage. Refer to the product label for precautions.