Creeping bentgrass (Agrostis stolonifera) is a cool-season turf highly valued for golf course putting greens due to its fine texture and ability to withstand extremely short clipping heights. However, when this grass appears in a standard fescue or bluegrass home lawn, it behaves like an aggressive, invasive weed. The primary concern is its rapid lateral expansion, which allows it to quickly colonize and degrade the appearance of mixed-species turf. Understanding the physical mechanisms that drive this fast expansion is essential for effective management.
The Primary Methods of Bentgrass Spread
The accelerated spread of creeping bentgrass is due almost entirely to its unique vegetative growth habit, driven by specialized above-ground stems called stolons. These stems radiate horizontally across the soil surface, forming a dense, woven mat that aggressively pushes into surrounding turf. As the stolons travel, they root down at their nodes, allowing new, genetically identical plants to establish quickly and independently from the parent plant.
This network of rooting stolons enables bentgrass to cover ground at a speed that turf-type grasses cannot match, making it the main engine of rapid patch expansion. A single plant can send out runners that establish new patches several inches away in a short period under favorable conditions. The secondary method of dispersal is through seed production, which occurs when the grass is allowed to mature. These minute seeds are easily carried by wind, water runoff, or adhering to mowing equipment and footwear.
The highly invasive nature of an established patch is primarily a result of the stoloniferous habit, even though seeds can remain viable for a year or more. Any mechanical disruption, such as improper aeration or aggressive dethatching, can inadvertently break stolons into fragments. Each fragment retains the ability to root and establish a new plant, effectively multiplying the problem and accelerating the infestation across a wider area.
Environmental and Cultural Factors That Accelerate Growth
The speed at which creeping bentgrass spreads is highly sensitive to external conditions and management practices. The cultural environment, particularly the height of the cut, is the most influential factor determining the rate of stolon growth and establishment. When the grass is mowed very low, the plant is forced to produce dense, low-growing stolons. This promotes maximum horizontal expansion and turf density, which is standard practice on golf greens.
Conversely, a higher mowing height (three to four inches) forces the bentgrass to grow more upright. This elevated cut stresses the plant and shades the soil, suppressing the production and rooting of new stolons and significantly slowing the rate of spread. Moisture is another powerful accelerator, as bentgrass possesses a shallow root system compared to fescue or bluegrass. Frequent, shallow watering creates a consistently moist upper soil layer that the bentgrass favors, encouraging runners to root quickly and grow vigorously.
Deep and infrequent irrigation promotes the deeper root growth of desirable turf species, creating a drier surface layer less favorable for bentgrass stolon establishment. High nitrogen fertility also directly fuels bentgrass expansion by promoting vegetative growth. Nitrogen application rates designed for maximum growth in cool-season turf can encourage a lush, fast-spreading mat of runners and increase thatch accumulation.
The physical condition of the soil also plays a role in the speed of colonization. Bentgrass thrives in a well-aerated environment and tolerates some soil compaction. Excessive thatch accumulation is a problem because thatch, a layer of organic matter between the soil and the grass blades, provides an ideal medium for stolons to travel and root without needing to penetrate the dense soil below.
Strategies for Containment and Removal
Addressing an established creeping bentgrass infestation requires a multi-pronged approach combining cultural, physical, and chemical strategies. For small, isolated patches, physical removal is the most immediate and effective method. This involves digging out the entire patch, removing the soil to a depth of several inches, and extending the perimeter at least six inches beyond the visible patch to ensure all stolons are extracted.
After physical removal, the primary strategy for long-term containment involves reversing the cultural practices that favored the weed. Raising the mowing height to three inches or more stresses the bentgrass and gives the desired turf a competitive advantage by shading the soil and suppressing stolon growth. Shifting irrigation to deep, infrequent cycles will also dry out the surface layer, inhibiting the bentgrass’s shallow rooting ability.
Chemical control is often necessary for widespread infestations, though it is challenging since bentgrass is a grass growing within a grass lawn. Non-selective herbicides, which kill all plant tissue they contact, are highly effective for spot-treating individual patches. This requires accepting a temporary dead spot, followed by re-seeding or re-sodding the area after the herbicide has taken effect.
A more selective approach involves using specialized herbicides, such as those containing mesotrione, which can suppress or control bentgrass with less harm to cool-season turf varieties like fescue and bluegrass. These selective applications often require multiple treatments over several weeks to weaken the persistent stolon network. Consistency in cultural control is necessary to prevent the rapid re-establishment of the invasive grass from any remaining fragments or seeds.