This Invasive Weed has Taken Over the Front Garden

(Question)

Can you please identify the weed in the attached photo?  Over several years, it has strangled out our hostas and other plants and has a very long tenacious root system.  Do we have to dig everything up for 1 foot and start again, or can we save our good plants and replant them without reintroducing this weed?  Thank you very much for any assistance you can provide.

image

(Answer)

Unfortunately I think you have an infestation of Aegopodium podagraria, commonly known as Goutweed, Bishop’s weed or Snow on the mountain.  It is a very invasive and difficult plant to get rid of once it is in your garden, but it’s not impossible.  This plant is a member of the Carrot family and comes in either solid or variegated varieties.  The solid form is a much more vigorous grower than the variegated form, and can take over a flower bed in no time.

There are several ways that you can tackle the problem, none of which will require you to discard your Hostas or other plants, but will require patience and a lot of work.

Don’t allow goutweed to bloom, and if it does, make sure you cut off any flowers before seed production in order to stop local spread, with seeds germinating into new plants.

Goutweed is mainly spread by rhizomes though, as it has an extensive root system and will propagate from any tiny root fragment in the soil.  You have a choice of techniques to eradicate the existing plants.

Dig up the goutweed and other plants in the infested areas.  You must remove ALL of the roots of the goutweed and this is best done by digging and raking the soil after the plants have been taken up.  You should remove soil as necessary from the roots of your other plants (Hostas) before replanting, to ensure that they are not hiding goutweed root fragments.  This process must be repeated in the infested beds, and you may have to do it for a number of years.  The plants you removed can be replanted elsewhere, either for a short term until they can be returned to the goutweed free beds, or on a permanent basis.

The other method is starve the roots of the goutweed by cutting the leaves down in early spring, and again each time they start to grow until eventually the roots die.  The rhizome starch/food reserves are lowest in spring so control is easiest then.  Alternatively, the same result can be achieved by removing the plants you want to keep (ensuring they are goutweed root fragment free), cutting down the plants and then covering the infested beds with cardboard or thick layers of newspaper, covered with another thick layer of mulch.  This will starve the goutweed of the light it needs to photosynthesise and make food, but may have to be left in place for a full year.  Eventually, when nothing is found to be sprouting up, this can be planted through.

The goutweed, including roots, should not be put into your compost.