Ask Mr. Smarty Plants

Well, as you suspect goutweed or Bishop's weed (Aegopodium podagraria) is a real menace! Goutweed is native to Eurasia but has been introduced around the world as an ornamental plant and has now become an invasive exotic plant. And the variegated version isn't much better.

Here's what a couple of experts at the UBC Botanical Garden say about the plant in answer to a gardener's (Gayle) request for ideas on how to remove it that was published in The Vancouver Sun online. It doesn't matter where goutweed grows it acts in the same invasive way ...

On Gayle’s behalf, I consulted the experts at the UBC Botanical Garden. Douglas Justice teaches in the landscape architectureprogram and is the curator of collections for the botanical garden. Douglas responds, thusly: Aegopodium podagraria. Pernicious as hell. Copious seeds and elastic rhizomes. Tolerates any kind of soil and full sun to heavy shade. Drought tolerant in deep soil. Only need a tiny rhizome piece to start a whole new colony. Dig it out and the roots go deeper. Very frustrating. Like other aggressive runners, extraction/elimination requires wholesale (though not necessary permanent) change to the affected area. Converting the area to turf for three years or very heavy mulching (leaf mould, chips, whatever, at 20 to 30 cm deep) are two approaches that can be effective.

Unless [nearby] plants are woody and relatively large, they should be lifted, cleaned thoroughly and put aside or planted elsewhere (obviously, this has to be done when plants are dormant). Deep mulching encourages the goutweed rhizomes to find a higher plane, which, if the mulch is kept loose, makes extraction relatively simple, but the removal must be religious. A maintained sward of good turf (start with sod, not seed) will starve/exhaust/prevent regrowth. Rhizomes will be completely dead after three years; however, when returning the area to planting bed, seedlings may be an issue.

Otherwise, the plants are apparently “medicinal” and the new shoots edible.

I also received a response from the UBC Botanical Garden Hortline:

Indeed, “goutweed” is a real challenge to remove. As Douglas mentioned it will be very important to remove any lingering goutweed roots from your existing plants because they regenerate quickly even if you dig them up and place elsewhere in your garden they will soon send out new shoots. I was able to eradicate a small area of my vegetable garden by digging down 2 1/2 feet, removing all the roots of goutweed (as well as the plants) and allow the area to sit fallow for 6 months covered with black plastic. After six months I brought in new soil and re-planted. After 2 years there has been no return of goutweed.

For what it’s worth, the best way I have found to eliminate really difficult weed infestations is by solarizing. Cover the area with a sheet of black plastic and let the sun cook everything.