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False shamrock, aka woodsorrel, is a weed we notice around St. Patrick’s Day

It’s been said that one person’s wildflowers are another person’s weeds. This saying applies particularly well to a large group of low-growing herbs in the Oxalis genus.

The name Oxalis indicates the presence of oxalic acid in many of the approximately 500 plant species within the genera. Many of the species are known as woodsorrels as they have an acidic taste reminiscent of the unrelated sorrel. Some species are called yellowsorrels or pinksorrels after the color of their flowers instead. Other species are informally known as false shamrocks. They are also known as sourgrass because of their sour-lemony tasting leaves.

Woodsorrels are frequently sold as potted houseplants. Around St. Patrick’s Day, it is common to see stunning purple or green shamrock shaped leaved plants with splendid white, pink or purple flowers. While they do make nice houseplants, be aware that these plants can become weeds in the landscape.

By far, Extension’s most common encounter with woodsorrel will be gardeners’ complaining about them as weeds in their lawns. There are several species of woodsorrel that are troublesome weeds in Northwest Florida.

Creeping woodsorrel

This low growing, prostrate creeping weed is known botanically as Oxalis corniculata. It typically stands no more than a couple of inches tall but the stems can grow to twenty inches long. The stems are slender and delicate, breaking easily when hand pulled. Leaves consist of three heart-shaped leaflets which fold down around the stem at night or when the plant is stressed.

The flowers have bright yellow petals and occur in clusters at the tips of long stalks. Flowers eventually produce seeds that reside in elongated, lantern-shaped seedpods. Each seedpod can hold up to 50 seeds. A single plant can produce up to 5,000 seeds. When the seeds mature, the pod will turn downward and forcefully discharge the seed into the surrounding area. They germinate whenever temperatures are between 60 and 80 degrees F.

Although this is a perennial plant and reproduces vegetatively by rooting from its stems, its primary means of reproduction is by seed.

In flowerbeds, a two to three inch layer of mulch can block the light necessary for creeping woodsorrel to germinate. This weed growing in a lawn presents a difficult challenge since mowing does not provide good control and hand-removal can be difficult due to the fragile stems.

Creeping woodsorrel is low growing and spreads by rooting from its stem

Southern yellow woodsorrel

Oxalis stricta is similar to creeping woodsorrel but has more of an upright habit and does not root from its stems.

This herbaceous perennial has hairy stems and deeply-cut heart-shaped lobed leaves that can be green to reddish-purple. It arises from tough underground stems called rhizomes and tends to form clusters of plants.

The underground rhizome of yellow woodsorrel

Pink woodsorrel

Pink wood sorrel is an escaped exotic ornamental plant that is now found throughout Florida. It is native to tropical America. Pink wood sorrel is similar to yellow woodsorrel but has pink flowers from spring through fall.

Pink woodsorrel will have pink flowers

Control options

When occurring in flowerbeds, remove as much woodsorrel as possible by hand. Concentrate on removing the rhizomes or underground structure of the weeds. Appropriately applied and maintained mulch will reduce seed germination. If hand removal is not an option, apply a non-selective herbicide labeled for flowerbeds such as glyphosate.

In lawns, be sure to maintain a healthy stand of turf by mowing, fertilizing and watering correctly. Apply pre-emergence herbicides at the proper time in the spring. Treat existing woodsorrel with a post-emergence herbicide that is safe to use on your particular type of turfgrass. For a listing of recommended herbicides, refer to the UF/IFAS publication entitled “Yellow Woodsorrel (Oxalis) Biology and Management in Turf.” It’s available online at http://edis.ifas.ufl.edu/ep385 or by calling your local Extension Office.

Theresa Friday is the Residential Horticulture Extension Agent for Santa Rosa County. The use of trade names, if used in this article, is solely for the purpose of providing specific information. It is not a guarantee, warranty, or endorsement of the product name(s) and does not signify that they are approved to the exclusion of others.  For additional information about all of the county extension services and other articles of interest go to: http://santarosa.ifas.ufl.edu.

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Permanent link to this article: http://santarosa.ifas.ufl.edu/blog/2012/03/06/false-shamrock-aka-woodsorrel-is-a-weed-we-notice-around-st-patricks-day/