Depressed clearweed is a common, widespread plant that often becomes a persistent problem in garden beds, lawns, and container plantings. This low-growing, mat-forming herb quickly colonizes disturbed areas, competing with turfgrass and ornamental species for resources. Managing this aggressive species requires understanding its unique biology and implementing effective control strategies. This guide details how to identify this persistent plant and implement effective control measures.
Identifying Depressed Clearweed
Accurate identification is the first step in managing this tenacious invader, scientifically known as Pilea microphylla. It is also recognized by the common names Artillery Plant or Gunpowder Plant, which hint at its unique method of seed dispersal. This short-lived perennial or annual grows low to the ground, forming dense, cushion-like mats that can spread up to two feet wide.
The foliage is its most distinctive feature, consisting of abundant, tiny, light-green leaves that appear almost succulent-like and are typically less than a quarter-inch long. These small, rounded leaves grow on smooth, highly branched, and often translucent stems. Depressed clearweed thrives in moist, disturbed areas, frequently establishing itself in cracks of sidewalks, between pavers, or in rock mulch beds. While it prefers partial shade, it can tolerate full sun, especially with consistent irrigation.
Understanding Its Invasive Nature
The difficulty in managing Pilea microphylla stems from its efficient, dual-pronged approach to reproduction. The plant reproduces both by producing seeds and through vegetative growth, rooting easily from small stem fragments. Its low-growing, mat-forming habit allows it to quickly establish a strong presence, outcompeting other plants.
The plant’s remarkable mechanism for broadcasting its seeds is why it is called the Artillery Plant. When the male flowers mature, they explosively eject pollen and tiny seeds into the air, launching them several feet away. This ballistic dispersal ensures the plant rapidly spreads over a wide area. Furthermore, the plant’s ability to regrow from small pieces of root or stem means that physical disturbance can unintentionally lead to new colonies.
Effective Control and Removal Methods
Effective control of depressed clearweed requires a multi-faceted approach combining manual, cultural, and chemical methods. The strategy must address both established plants and the persistent seed bank to achieve long-term success. Focusing on young plants and changing the environment to make it less favorable for growth are important first steps.
Mechanical/Manual Removal
Hand-pulling is a viable option for managing small, isolated patches before they become large infestations. This method provides immediate removal of the plant material and is effective when performed thoroughly. However, the entire root system must be removed, as the plant easily regenerates from small pieces of root or stem left behind.
When manually removing the weed, pull the whole plant slowly and carefully to prevent brittle stems from breaking and leaving fragments. All plant fragments or uprooted material should be promptly bagged and removed from the area to prevent re-rooting or seed dispersal. If the plant has already flowered, pulling it can trigger the explosive seed launch, so performing this task before flowering begins is beneficial.
Cultural/Environmental Control
Changing the environmental conditions is a highly effective, long-term strategy for making the area less hospitable to the moisture-loving weed. Since Pilea microphylla thrives in moist, shaded environments, improving soil drainage and increasing light exposure can help suppress its growth. Adjusting irrigation practices to reduce surface moisture and avoid overwatering is a practical cultural control measure.
Applying a thick layer of organic mulch, such as wood chips or shredded bark, physically suppresses the weed and prevents tiny seeds from reaching the soil surface. A mulch layer of at least three inches blocks sunlight and reduces the plant’s ability to establish itself. Maintaining good garden sanitation, such as using weed-free potting media, also prevents the accidental introduction of seeds or stem fragments.
Chemical Control
For large or widespread infestations, herbicides may be necessary to gain control. Postemergence herbicides, applied directly to existing plants, provide effective control when used correctly. Active ingredients such as flumioxazin, oxadiazon, and indaziflam have demonstrated excellent long-term control by preventing regrowth.
Contact herbicides, like those containing pelargonic acid, work quickly to burn down foliage but provide only temporary control, often requiring repeat applications. Preemergence herbicides, applied to the soil before seeds germinate, are highly effective against this prolific seed producer. Common preemergence active ingredients like prodiamine or pendimethalin create a barrier that prevents tiny seeds from successfully sprouting. When applying any chemical control product, strictly follow the label directions regarding application rates and safety precautions to protect desirable plants and the environment.