Torpedo grass does not die in winter but enters a state of dormancy to survive colder months. This aggressive, perennial weed is known for its hardiness and ability to persist, classifying it as one of the world’s worst weeds in tropical and subtropical regions. This biological strategy allows it to maintain its presence and return vigorously when warm weather returns.
The Mechanism of Cold Survival
The ability of torpedo grass to survive cold temperatures depends entirely on its subterranean structure. The plant allocates a significant portion of its biomass, sometimes up to 87%, to its extensive network of underground stems, called rhizomes. These rhizomes function as robust storage organs, accumulating large reserves of carbohydrates and energy. This stored energy acts as the plant’s winter survival kit, insulating the core structure from freezing conditions.
The rhizomes are coarse, long-lived, and feature sharp-tipped growing points, which is the source of the plant’s common name. They are primarily found within the top two feet of the soil, though some penetrate much deeper. This deep-seated root mass protects the regenerative buds along the rhizome from surface cold. The protected underground reserves allow the plant to rebound quickly, even if it is sensitive to prolonged cold.
Visual Changes During Dormancy
The visual appearance of torpedo grass during winter often leads homeowners to mistake dormancy for death. When consistent temperatures fall below 50°F, the above-ground foliage begins to die back. The green blades turn uniformly brown or straw-colored, signaling the onset of dormancy. This superficial change is a natural response to conserve energy and is not an indication that the plant has been killed.
This dieback is common among warm-season grasses sensitive to frost. The plant is simply channeling its resources into the protected underground rhizomes. The seemingly dead, straw-like appearance is a temporary phase that masks the living survival mechanism operating beneath the soil surface.
Post-Winter Recovery and Spread
As temperatures begin to warm in early spring, often before other turf grasses, torpedo grass rapidly breaks dormancy. The immense energy stores accumulated in the rhizomes allow for a quick and aggressive re-emergence. New shoots sprout from the numerous regenerative buds along the underground stems, leading to a quick return of green foliage.
This stored energy enables a rapid growth rate, with new rhizome fragments capable of growing over half an inch per day in favorable conditions. The established network of rhizomes is not killed by the cold and fuels the plant’s immediate spread upon recovery. Since cold weather does not reduce the density of the existing root mass, the weed increases its territory aggressively year after year.
Practical Control Strategies During Dormancy
The dormant period offers a strategic window for control efforts because the plant’s above-ground growth has stopped. One of the most effective mechanical methods during this time is physical removal, which requires meticulous attention. Digging up the rhizomes is a viable option for small infestations, especially when the soil is soft and workable.
It is necessary to remove the entire rhizome system, including the sharp, white tips, because even small fragments can regenerate into a new plant. All removed material should be disposed of in sealed bags and not composted, as the fragments will easily sprout.
From a chemical standpoint, the dormant season is a time for preparation and specific application timing. Non-selective herbicides like glyphosate are used for eradication, but they must be applied when the grass is actively growing to be effective. Therefore, the dormant period should be used to plan a high-concentration application for early spring when the first new shoots appear, or a late-fall application before deep dormancy sets in.
Some control programs recommend applying a pre-emergent herbicide labeled for crabgrass in the fall. This suppresses potential seedling germination, preparing the area for a more targeted post-emergent attack in the spring.