Goutweed (Aegopodium podagraria), often called Bishop’s Weed or Ground Elder, is a highly aggressive invasive perennial species that poses a significant challenge for gardeners. It rapidly colonizes garden beds, forming dense patches that suppress desirable landscaping. Successfully eliminating an infestation requires a multi-season commitment and a strategic approach targeting the plant’s unique biology.
Understanding Goutweed and Its Aggressive Spread
Goutweed is a member of the carrot family, recognizable by its compound leaves typically divided into three groups of three leaflets. The all-green “wild” type is the most problematic due to its aggressive spread. Mature plants may produce small, white flowers clustered in flat-topped umbels during the summer.
The difficulty in eradication stems from its underground structure: a vast network of white, fleshy rhizomes. These horizontal stems spread rapidly, allowing the plant to quickly dominate large areas. A single, small fragment of a broken rhizome can sprout a new, independent plant. This ability to regenerate means that any disturbance, such as tilling, actually serves to propagate the weed.
Manual and Cultural Eradication Techniques
Manual and cultural methods offer non-chemical solutions for small patches, though they demand significant time and persistence. The most direct method is meticulous hand-digging, which requires removing the entire plant, including every section of the rhizome. This process is best performed when the soil is moist, allowing for easier extraction of the underground stems.
In heavily infested areas, simply digging is often insufficient, necessitating the labor-intensive process of soil sifting. Excavating the affected soil to a depth of at least a foot and then carefully screening it ensures that even the smallest rhizome fragments are removed. Once cleared, vigilant monitoring is necessary, as new sprouts may emerge for several seasons, requiring immediate removal.
For larger, open areas, light exclusion techniques like smothering or solarization can be effective. Smothering involves cutting the goutweed down and covering the area with thick, opaque material, such as heavy black plastic or cardboard. This must remain in place for at least one full growing season to fully exhaust the carbohydrate reserves in the rhizomes.
Solarization is feasible in full-sun locations during the hottest months, utilizing clear plastic to trap solar heat. After cutting the goutweed low and watering the soil, clear plastic should be tightly sealed and left in place for a minimum of six weeks.
Selecting and Applying Chemical Treatments
For extensive infestations, a targeted chemical approach using a systemic herbicide is a viable option. Contact herbicides are ineffective because the plant quickly regrows from its rhizome reserves. A systemic, non-selective herbicide, such as one containing glyphosate or triclopyr, is necessary because it is absorbed by the leaves and transported down to the roots, killing the entire plant.
The most effective time to apply these chemicals is when the plant is actively growing, generally from late spring through early fall. Application is particularly effective in the fall, as the weed is transporting carbohydrates to its roots for winter storage, pulling the chemical along. The treatment should be applied directly to the foliage, following product label instructions precisely for dosage and safety.
Because goutweed has substantial underground reserves, repeated treatments are required. Applications should be spaced several weeks apart to target new growth emerging from surviving fragments. Use extreme caution, as non-selective herbicides will harm desirable plants, necessitating careful application to minimize drift.
Long-Term Prevention and Containment Strategies
Once the bulk of the infestation is removed, the focus must shift to long-term containment and prevention. The first step is the correct disposal of the removed plant material to prevent re-infestation. Goutweed rhizomes should never be added to a home compost pile. All plant material must be dried out completely and then sealed in bags for municipal garbage collection or burned where permitted.
To prevent re-invasion from neighboring properties or untouched areas, installing a solid physical barrier is highly effective. Root barriers, such as thick plastic sheeting or metal edging, should be sunk vertically into the ground to block the creeping rhizomes. The barrier needs to extend at least 12 to 18 inches deep and protrude a few inches above the soil line.
The newly cleared area should be monitored vigilantly, removing any stray sprouts immediately to deplete their reserves. This bare soil should then be quickly covered with a dense, competitive planting of desirable groundcover. The goal is to occupy the space and shade the soil, eliminating the light and space residual fragments need to re-establish themselves.