Oxalis

Q: We have a small shamrock-like plant growing in various lawns and flower beds. We have tried to control it, but it seems to be a very difficult problem. A: The weed is oxalis. It has several other aliases including woodsorrel, sourgrass, or wood shamrock. Oxalis compromises a group of similar plants that hybridize and form various subspecies. Control is not easy. Oxalis has a unique method of seed dispersal. As the seed capsules mature during the summer, the internal pressure increases and an elastic jacket bursts and throws the seed as far as 6 feet away. The seeds germinate and start new plants quickly. Perennial woodsorrel is a serious problem in greenhouses, woody ornamentals, gardens and lawns. It roots at each node on long, slender runners which makes it difficult to remove by cultivation or hand-pulling. It is difficult to eliminate chemically because it is resistant to most herbicides. The woodsorrels all have clover-like or shamrock type leaves and have a distinctive sour taste because of the oxalic acid content. The leaves are green or reddish in color. Most species have shallow, fibrous roots and the weed species have small, yellow five-petaled flowers all summer. In addition, some woodsorrels have deep roots with small bulblets that make control more difficult. Use products containing dicamba, trimec or triclopyr (Turflon D, etc.). Control in flower gardens requires consistent sultivation and possibly spot treatment with glyphosphate (Roundup) or other products. Landscape fabrics keep the plants from becoming deep rooted and difficult to control. Pre-emergent herbicides, like the ones used for spurge, can be applied next spring to prevent new seedling plants from developing. The weed is always difficult to control and requires repeated treatments of chemicals and cultivation.