Ice plant is a general term for several genera of succulent groundcovers, most notably Carpobrotus and Delosperma, known for their fleshy leaves and vibrant, daisy-like flowers. The plant has gained notoriety as a highly aggressive groundcover capable of forming dense, sprawling mats. The rate of spread is not uniform, depending heavily on the specific variety and the environmental conditions it encounters. Understanding the mechanisms of this plant’s expansion is key to predicting and managing its presence in a garden or natural area.
Differentiating Fast-Spreading and Slow-Growing Varieties
The speed of ice plant spread depends heavily on the variety. The most concerning and fastest-spreading type is the highly invasive Hottentot Fig, Carpobrotus edulis. This species is responsible for the plant’s reputation as an aggressive colonizer, particularly in coastal environments where it was often planted for erosion control.
In contrast, common ornamental ice plants, such as those in the Delosperma genus, are much slower and less aggressive. These varieties are preferred for rock gardens and small-scale groundcover because they are more compact and contained. While they spread to form mats, their growth is moderate and less likely to overwhelm neighboring plants. Aggressive varieties like Carpobrotus edulis are capable of the most rapid territorial gain, with individual shoots growing more than three feet (one meter) per year under ideal conditions.
The Dual Mechanisms of Ice Plant Expansion
Ice plant expansion occurs through two primary methods: rapid local growth via vegetative runners and long-distance colonization via seed dispersal. The most immediate spread comes from the vegetative growth of its fleshy, horizontal stems, known as runners or stolons. These runners creep along the ground surface, and any segment of the stem can produce new roots at the nodes when it contacts the soil. This allows the plant to form a continuous, dense mat that can expand in diameter by up to several feet per growing season. Individual clones of the invasive Carpobrotus edulis have the potential to grow to at least 165 feet (50 meters) across.
Seed Dispersal
Seed dispersal is crucial for long-distance colonization, though it is a slower process. Ice plant produces a fleshy fruit containing hundreds of seeds, often eaten by animals like deer, rodents, and rabbits. The seeds are dispersed when animals excrete them, and passage through the digestive system can enhance germination. Water also moves seeds, especially in coastal areas where fruits can be washed away by tides and currents. These seeds can remain viable in the soil for at least two years, allowing for the establishment of new colonies across a wider geographical area.
Environmental Influences on Growth Rate
The actual rate of spread is heavily influenced by surrounding environmental factors. Water availability is a major accelerator of spread, even though ice plant is well-known for its drought tolerance. While the plant survives with minimal water, rapid vegetative spread requires consistent moisture. Areas near irrigation runoff or with consistent rainfall will see a significantly faster growth rate in runners than arid locations.
The composition of the soil also affects how quickly the plant establishes new roots. Well-draining, sandy soils, like those found in coastal environments, facilitate faster runner growth compared to heavy clay soils. Furthermore, growth is maximized by full sun exposure and warm temperatures, allowing for continuous growth in milder climates. Shade or cold temperatures significantly slow the metabolic rate and the speed at which new runners establish roots.
Controlling and Containing Ice Plant Spread
Since vegetative runners are the fastest mode of expansion, containment efforts must focus on limiting this growth mechanism. One effective preventative measure is the installation of physical barriers, such as root barriers or deep edging, around the perimeter. These barriers prevent horizontal runners from touching the soil outside the designated zone and rooting at the nodes.
Water management is another powerful tool to regulate the speed of spread. Since rapid growth is fueled by consistent moisture, limiting irrigation near the edges of the patch will naturally slow the production of new runners. Allowing the soil at the perimeter to remain drier curtails the plant’s expansive efforts. Regularly inspecting the edges and mechanically pruning runners before they establish roots is an effective manual control method that significantly reduces the overall rate of spread.