Oxalis, commonly known as wood sorrel or shamrock plant, is a large genus of flowering plants found across the globe. It is known both as a desirable ornamental species and as a persistent garden weed. Its tendency to appear unexpectedly in lawns and flowerbeds often leads to questions about its basic growth habits. Determining whether a particular type is an annual or a perennial is the first step toward effective management or cultivation.
Defining the Oxalis Life Cycle
The genus Oxalis contains hundreds of species, which exhibit a range of life cycles. While some varieties are classified as annuals, completing their entire life cycle from seed to death within a single growing season, the most common and problematic species are perennials. A perennial plant lives for more than two years, often surviving unfavorable conditions by going dormant.
The persistence of perennial Oxalis stems from specialized underground structures that act as nutrient storage organs. These can take the form of small bulbs, tiny bulbils, corms, or rhizomes, depending on the species. For instance, species like the aggressive Bermuda Buttercup (Oxalis pes-caprae) produce numerous bulbils. These structures store energy and allow the plant to survive when the above-ground foliage dies back due to cold or heat. If a plant is pulled from the soil, the small, brittle bulbils often detach and remain behind. Each remaining bulbil or piece of rhizome has the capacity to sprout a new plant, allowing the plant to regenerate rapidly.
Key Characteristics for Identification
Identifying Oxalis is usually straightforward due to its distinctive foliage. The leaves of most species are trifoliate, meaning they are divided into three leaflets, which gives them a clover-like appearance. These leaflets are typically heart-shaped or obcordate, with a notch at the tip. Leaf color can range from bright green to deep reddish-purple, such as in the ornamental Oxalis triangularis.
The leaves exhibit nyctinasty, folding up at night or in response to environmental stress like intense light or touch. The plant produces small flowers with five petals, which can vary in color from yellow, pink, or white depending on the specific species. These flowers are usually borne singly or in small clusters on slender stalks.
Following flowering, the plant forms small, cylindrical seed capsules. When these seedpods mature, they are designed to burst open explosively upon contact or drying. This mechanism launches tiny seeds several feet away from the parent plant, contributing significantly to the plant’s spread.
Managing Oxalis Based on Its Growth Habit
The perennial nature of many Oxalis species dictates that management must focus on eliminating the underground structures. Surface weeding or mowing is ineffective for weedy perennial varieties because it only removes the foliage, leaving the energy-storing bulbs, corms, or rhizomes intact to resprout. Mechanical removal, such as digging, must be exhaustive to ensure all small, brittle bulbils are collected.
For larger infestations, systemic herbicides are typically more effective than contact herbicides. Systemic products are absorbed by the leaves and then transported internally throughout the plant, including down to the underground storage organs, destroying the entire structure and preventing regeneration. The timing of herbicide application is most effective during the plant’s active growth period when it is transporting nutrients to the roots.
Conversely, the perennial habit is valued in ornamental Oxalis varieties. Cultivation of plants like Oxalis triangularis involves ensuring the bulbs or rhizomes survive the plant’s natural dormancy period, which often occurs during winter or summer heat. Gardeners often cease watering and move the pots to a cool, dark place to allow the bulbs to rest and conserve energy for the next growing season.