Bishop’s Weed (Aegopodium podagraria) is an aggressive perennial ground cover that poses a significant challenge to gardeners and landscape managers. Originally introduced as an ornamental plant from Europe and Asia, it has earned a reputation as an extremely persistent and invasive garden pest. Complete eradication of this weed requires a comprehensive, multi-year strategy involving diligence and patience.
Why Bishop’s Weed Is So Difficult to Eliminate
The difficulty in eliminating Bishop’s Weed stems almost entirely from its underground structure: a dense, extensive network of white, fleshy rhizomes. These rhizomes are the plant’s primary means of reproduction and spread, allowing it to sprawl aggressively and suffocate other plants in the area.
The rhizomes are highly brittle, meaning that any attempt to dig or till the soil inevitably breaks them into small fragments. Even a tiny piece left behind can quickly regenerate into a new, vigorous plant. This regenerative ability means that standard weeding or shallow cultivation can actually worsen the infestation by multiplying the number of plants.
Non-Chemical Removal Techniques
Manual removal is feasible for small, contained areas, but it demands meticulous attention to detail to prevent re-establishment. The process involves carefully digging up the soil to a depth that captures the entire rhizome network, often requiring a garden fork to loosen the soil and minimize breakage. Sifting through the excavated soil is necessary to ensure every fragment is removed, as any remnant can sprout anew.
A more effective non-chemical approach for larger areas is smothering, which deprives the plants of sunlight for an extended period. This technique involves mowing the Bishop’s Weed low and then covering the area with a thick, opaque barrier like black plastic or overlapping layers of cardboard. The barrier must be secured and left in place for a minimum of one full growing season, often one to two years, to completely starve the deep root reserves.
Alternatively, repeated cutting of the foliage can exhaust the underground root reserves over time. This method involves cutting the plant as close to the ground as possible, ideally once a week during the growing season, preventing photosynthesis. This continuous defoliation starves the rhizomes, but typically requires diligent repetition for three to five years to achieve significant reduction. All removed plant material, including leaves and rhizomes, must be disposed of properly to prevent re-establishment. Debris should be bagged and sent to a landfill or incinerated, not added to a compost pile, as fragments can survive.
Effective Herbicide Application Methods
For severe or widespread infestations, a chemical approach using systemic herbicides is the most practical solution. Systemic herbicides, such as those containing glyphosate or triclopyr, are absorbed by the foliage and translocated throughout the plant’s vascular system, traveling down to the rhizome network to kill the entire structure. Contact killers are ineffective because they only burn the above-ground leaves, allowing underground reserves to quickly push up new growth.
Timing the application is a factor for success because the herbicide must be applied when the plant is actively moving nutrients downward. The optimal time for application is in the late summer or early fall, when the plant is preparing for winter dormancy and transporting sugars to its roots for storage. This downward flow efficiently carries the systemic chemical to the rhizomes, maximizing its destructive effect.
A strategic preparation method involves cutting the foliage back completely and then allowing the plant to regrow a fresh flush of leaves before spraying. This new, tender growth absorbs the herbicide more efficiently than older leaves. When applying the product, carefully follow all label instructions and use a shield, such as cardboard, to prevent drift onto desirable plants, as these herbicides are non-specific total vegetation killers. Multiple applications over several seasons are usually necessary to fully eradicate Bishop’s Weed, and treating any regrowth the following spring continues the long-term elimination strategy.
Long-Term Monitoring and Site Restoration
The fight against Bishop’s Weed continues after the main eradication effort is completed. The area must be monitored diligently for at least two to three years for any signs of emerging seedlings or the regrowth of missed rhizome fragments. Any new sprouts should be removed immediately to prevent the re-establishment of the patch.
To protect treated areas from re-invasion, physical barriers can be installed, especially near adjacent infested properties. Sinking deep landscape edging material, such as metal or heavy plastic, into the ground to a depth of at least 18 to 24 inches provides an effective barrier against creeping rhizomes. This step helps protect cleared garden beds.
Once the Bishop’s Weed is successfully removed, the final step is to restore the site by planting dense, competitive vegetation. Leaving the soil bare creates an open invitation for re-infestation or the establishment of other weeds. Replacing the Bishop’s Weed with desirable ground covers or grasses, such as Golden Alexanders (Zizia aurea) or Canada Anemone, can occupy the space and prevent the invasive weed from regaining a foothold.