Commelina, or dayflowers, are a genus of plants found globally. While some species are cultivated for their vibrant, short-lived flowers, many are considered pervasive weeds in gardens and agriculture due to their rapid spread and persistent growth.
Identifying Commelina Species
Dayflowers generally exhibit a creeping or sprawling growth habit, with fleshy stems that can root readily at the nodes where leaves emerge. Their leaves are typically alternate, ranging in shape from oblong to lance-shaped, and feature parallel veins characteristic of monocot plants. A notable identification feature for some species, such as Benghal dayflower (Commelina benghalensis), includes reddish or white hairs at the tip of the leaf sheath.
The flowers of Commelina are unique, commonly displaying three petals. Two of these petals are typically larger and often bright blue or lilac, while the third petal is noticeably smaller and may be white or a lighter blue, sometimes appearing almost inconspicuous. These delicate blossoms emerge from a folded, leaf-like structure called a spathe. True to their common name, individual dayflower blossoms open in the morning and typically wilt by midday, lasting for only a single day. Certain Commelina species, like Benghal dayflower, also produce inconspicuous underground flowers in addition to their aerial blooms, contributing to their prolific reproduction.
Commelina in Gardens and Landscapes
Many Commelina species are troublesome weeds in gardens, agricultural fields, and managed landscapes due to their aggressive growth and adaptability. They thrive in a broad range of soil types, from full sun to partial shade, often colonizing moist, disturbed areas, and can withstand saturated soil conditions or temporary flooding.
This genus spreads prolifically through both seeds, produced above and below ground, and vegetative reproduction from stem fragments that readily root upon contact with soil. Their rapid proliferation can lead to dense stands that outcompete and displace desirable plants.
Effective Control Methods
Managing Commelina requires a consistent approach, often combining several methods. Manual removal is effective for small infestations, but it is important to extract the entire plant, including all roots and stem fragments, as these plants can easily re-root and regrow from even small pieces. Hand-pulling is most successful when the soil is moist, allowing for easier and more complete removal of the root system. Regular monitoring and repeated removal are necessary to deplete the seed bank and prevent new plants from establishing.
Cultural practices can also help suppress dayflower growth. Applying a layer of organic mulch, approximately 2 to 4 inches deep, can inhibit seed germination and reduce the emergence of new seedlings. Promoting a dense, healthy stand of desired plants, whether turfgrass or garden plants, can also help by outcompeting dayflowers for light, water, and nutrients. While mowing or cultivation can provide some temporary suppression, these methods are often not fully effective because broken stems can regenerate into new plants.
For widespread or persistent infestations, chemical control may be considered, though Commelina species can exhibit tolerance to certain herbicides, especially when mature. Multiple applications are often necessary for effective control.
Post-emergence herbicides like 2,4-D, bentazon, glufosinate, diquat, or pelargonic acid have shown efficacy on young plants. Combinations of active ingredients, such as cloransulam-methyl and sulfentrazone, are also effective. Pre-emergence herbicides like S-metolachlor, indaziflam, and flumioxazin can offer suppression by preventing seed germination.
Always review and adhere to product labels for appropriate application rates, timing, and safety precautions.