Oxalis, often recognized by its clover-like leaves and delicate flowers, is a widespread genus of plants. Gardeners frequently encounter varieties known as wood sorrel or shamrock plant. While some Oxalis species are cultivated for their ornamental appeal, a common question arises regarding their potential to become invasive. This concern stems from observations of their rapid spread in various garden settings.
Understanding Oxalis Invasiveness
An “invasive” plant species spreads aggressively outside its native range, outcompeting local flora and potentially disrupting ecosystems. Oxalis species often fit this definition, posing a significant challenge in gardens. Their rapid growth allows them to quickly colonize new areas, overshadowing less vigorous plants. Many varieties are highly adaptable, thriving in diverse soil conditions and light exposures. These traits contribute to their prolific spread and make them difficult to manage once established.
Common Invasive Oxalis Species
Among the numerous Oxalis species, certain ones are notorious for their invasive tendencies. Oxalis corniculata, or creeping wood sorrel, is a widespread example, recognized by its small yellow flowers and leaves that can range from green to purplish. This species often forms low-growing mats, invading lawns, flowerbeds, and potted plants. Another prominent invasive species is Oxalis pes-caprae, or Bermuda buttercup, which features bright lemon-yellow flowers on taller stems. Not all Oxalis varieties are invasive; for instance, Oxalis triangularis, with its striking purple foliage, is a popular ornamental that typically remains contained.
How Oxalis Spreads
Invasive Oxalis species employ several highly effective mechanisms for propagation, which contribute to their persistent nature. Many species produce small, underground reproductive structures known as bulbils, which are easily dislodged and can readily sprout new plants. These bulbils can remain viable in the soil for several years, making eradication difficult. Oxalis also reproduces prolifically by seed, which are contained in small, okra-shaped capsules. When mature, these seed pods explosively disperse their tiny seeds over considerable distances, sometimes several feet away from the parent plant.
Beyond seeds and bulbils, some Oxalis varieties spread through rhizomes or stolons. Rhizomes are underground stems that produce new shoots and roots, expanding the plant horizontally beneath the soil. Stolons are similar, creeping along the ground and rooting at nodes to form new plants. Oxalis’s adaptability to various growing conditions, including different soil types and light levels, further enhances its ability to spread. This multi-faceted reproductive strategy makes these plants challenging to control.
Managing Invasive Oxalis
Controlling invasive Oxalis requires persistent effort and a multi-pronged approach. Manual removal is effective for small infestations, but it is crucial to extract all parts of the plant, including any underground bulbils and root fragments, as remaining pieces can regenerate. Hand-weeding is often easier when the soil is moist, ensuring the entire plant can be removed. Regularly removing foliage can also help to deplete the energy reserves stored in the bulbs over time.
Cultural practices can also help deter Oxalis. Applying a 2-3 inch layer of mulch in garden beds can suppress seed germination by blocking light, as many Oxalis seeds require light to sprout. Maintaining a healthy, dense lawn or garden can create a less hospitable environment for Oxalis to establish, as vigorous desirable plants can outcompete it for resources. Ensuring proper watering and fertilization based on soil test results promotes strong plant growth, which in turn helps native or desired plants resist invasion.
For larger or more established infestations, chemical control using herbicides may be considered. Non-selective herbicides containing glyphosate are effective for spot treatment in landscape beds, but avoid contact with desirable plants. For lawns, selective broadleaf herbicides can target Oxalis without harming the grass. Pre-emergent herbicides prevent new seeds from germinating, while post-emergent herbicides treat existing plants. Always read and follow product labels carefully for proper application rates and safety precautions.