Whether you call it goutweed (as we will here), ground elder, bishop’s weed or any one of over its dozen other common names, Aegopodium podagraria is one of the most common groundcovers used in our gardens… and also one of the most pernicious weeds known to man. Once established, it spreads out in all directions thanks to its numerous horizontal underground rhizomes. It’s a very domineering plant, choking out other vegetation and even preventing trees and shrubs from germinating. In addition, it readily leaves gardens to invade nearby fields and forests, causing inestimable damage to the environment in countries where is it not native. And it is terribly difficult to control once it does get loose!
Know Thine Enemy
First a description.
Goutweed is native to Eurasia where it commonly grows in the dense shade of forests. It’s a umbellifer, that is, in the Apiaceae family. It’s closely related to the carrot and, in fact, damaged roots and leaves of goutwood give off a characteristic carrotlike odor.
The lower leaves are divided into three toothed, pointed leaflets while the upper leaves are twice ternate (each of the three leaflets is in turn divided into three more leaflets). While the species, A. podagraria, has plain green leaves, the form most commonly grown in gardens is A. podagraria ‘Variegata’, with variegated foliage: green leaves are edged in white. When variegated goutweed self-sows, though, it gives entirely green plants. That explains why entirely green plants often appear near plantings of the variegated form. The green form is even more vigorous and invasive than the variegated variety and when the two grow together, the green variety may eventually smother out the variegated one.
Goutweed can reach 50 to 100 cm tall when in bloom in mid-summer, topped par domes (umbels) of tiny white flowers. Its stems are hollow. Its roots can dig down deeply into the soil, sometimes to a depth of several yards (meters).
Goutweed mainly spreads via its creeping rhizomes and, like many plants that have chosen vegetative propagation as their main means of reproduction, rarely self-sows. That’s good news for gardeners, because at least you don’t have to worry (much) about having to suppress the plant’s flowers to prevent it escaping by seed.
Since goutweed will grow in almost any environment – sun or shade and soil that is rich or poor, moist or dry, acidic or alkaline, etc. – and has no natural enemies outside of its native Eurasia, once it has escaped, you can’t count on Mother Nature stopping it.
The very easiest way to get rid of goutweed is to move away. Yes, change houses. That may seem excessive, but I assure you that more than one gardener has sold their home because of an uncontrollable goutweed infestation that made gardening impossible.
I’m not a fan of herbicides and hesitate to use or recommend them. Even so, goutweed is amazingly resistant to herbicides and even non-selective herbicides, such as glyphosate (RoundUp), that kill almost everything green, are not very effective on goutweed, so multiple applications will be required if you use them. In addition, non-selective herbicides are not easy to use in a garden setting, as they kill everything, not just weeds, but ornamentals as well.
Hand pulling is rarely effective. Goutweed is one of those plants you can’t simply pull up: the roots reach down deep into the soil and simply won’t let go. In addition, any rhizome that escapes your control will result in a new plant. Even if you try your best at hand pulling, goutweed will generally soon be growing as densely as before.
Cultivating does an even worse job than hand pulling. It tends to chop the roots and rhizomes into pieces, some too small to be readily noticed and which are therefore left in the ground. And yet each piece will soon be a new plant. Cultivating therefore tends to create an even denser patch than the original one.
Rototillers and other motorized cultivators are probably the worst way to try and eliminate goutweed. Not only do they chop rhizomes into pieces (and we know what result that will give!), but then they also spread them far and wide!
It is possible to eliminate goutweed by deep digging then sifting the soil to remove all roots and rhizomes. Dig down to a depth of 2 feet (60 cm), then screen the soil using a soil sieve: ½ inch/1.25 cm screening will do. While there may well be roots going even deeper, the plant is very unlikely to regenerate from such a depth. Of course, this is a major job, even if you use a bulldozer or excavator to remove the soil (recommended), because properly sifting soil is a very slow process..
Mowing short, to about 1-inch (2,5 cm), will also eliminate goutweed, as this removes the plant’s access to its sole source of energy, sunlight: by chopping the plant so far back you’ll eliminate its leaves entirely, you’ll prevent any photosynthesis. However, you’ll have to repeat the process regularly, as the plant’s reaction to having its leaves cut off is simply to produce new ones as soon as possible. Even mowing to a more moderate height, one appropriate for lawn grasses (2 ½ to 4 inches/6 to 10 cm) will at least weaken goutweed considerably. That’s one reason it rarely spreads very far into closely cropped lawns.
Why not try eating your enemy? Goutweed is a popular vegetable in many countries. Spring shoots are soft and tasty, cooked or raw. One the plant starts to bloom, though, the leaves become bitter.
My Favorite Method
I find the easiest environmentally friendly way of getting rid of goutweed (other than moving) is to cover the sector with black tarpaulin. Without light, the plant will be unable to carry out photosynthesis, causing it to weaken and die. You’ll need to cover about 3 feet (90 cm) beyond the goutweed patch’s original spread, however, or it will try to creep out from under the tarp. Make sure the tarp lets in absolutely no sunlight. Some geotextiles, for example, are not effective, because they let some light through: before you buy it, hold a piece to a light to make sure it is opaque. Sometimes good ol’ black plastic tarp, available in any hardware store, is the best choice.
Place the tarp in the early spring, before or as the leaves come up. Leave it on for a full year to totally starve the plant of any light. You can cover the tarp with mulch and or put flower pots on it if you want to beautify the area as the treatment proceeds.
When you remove the tarp in the spring of the second year, the goutweed will be dead, having exhausted all its reserves. If you find one or two pale shoots still alive, just cut them to the ground: they’ll be so exhausted they won’t grow back.
Really thick mulch will also shade out goutweed all on its own. Not just a few inches, but a good foot (30 cm) of it. Mow the plant down first and pour it on. Again, a full year of darkness, starting in spring, will be needed.
A Vertical Barrier
Eliminating goutweed from your yard is not however enough: you also have to keep it from coming back.
The problem is that goutweed rarely stops at property lines. If you have a goutweed problem, your neighbor is likely to have one too. And if he doesn’t collaborate in controlling it, the plant will simply cross back over into your yard. If so, install a vertical barrier into the ground between the two lots… before you start your treatment. Although goutweed roots can grow deeply down into the soil, its rhizomes usually run horizontally within a mere 2 inches (5 cm) of the surface. That means a simple lawn border could theoretically stop them. But not just any lawn border! The rhizomes tend to grow downwards when they hit an obstacle, although not very deeply. A 4- or 6-inch bordure (10-15 cm) will not be deep enough. Use an extra-deep border, 8 inches (20 cm) or more.
A horizontal barrier, such as a sidewalk or a driveway, between an infested area and a clean one can also be fairly effective, but sometimes a few rhizomes will make it across over time and, if so, will need to be controlled rapidly before a new colony starts up.
Should You Try to Save Plants From an Infested Bed?
Since treating goutweed usually means covering or digging up an entire garden, one question that always comes up is how to save any plants that are growing in the sector being treated. Can you dig up and save shrubs, bulbs, perennials, etc., planting them somewhere else temporarily?
Yes you can, if you’re very, very careful. Dig up the plant and rinse off all its soil. Remove any goutweed rhizomes you see growing through its root ball. Now pot it up. Do not plant it in another part of the garden until it has undergone a 3-month quarantine in its pot. If no goutweed has appeared after 3 months, you’ve successfully eliminated it and you can replant the potted plant.
Often divisions of the plant are easier to control for rhizomes (with fewer roots, you’ll better to able to see them) and are therefore a better choice than trying to save the mother plant.
Easier yet, take cuttings. You can take cuttings of most perennials, shrubs, and even conifers, and since the cuttings grow aboveground while goutweed rhizomes grow below, there will be no risk of them hosting goutweed rhizomes.
Should Goutweed Be Banned?
Despite the environmental devastation caused by goutweed in North America, Australia, New Zealand and other countries where it has escaped from culture (it’s easy enough to find entire forests where there is no regeneration whatsoever of local trees and where all native understory plants have been entirely eliminated by goutweed), goutweed, and especially its variegated form (A. podagraria ‘Variegata’), is still widely sold to unsuspecting gardeners in nurseries throughout the temperate world. In some American states, however, including Connecticut, Massachusetts and Vermont, the import and sale of goutweed is now banned, a step that at least helps slow the plant’s invasion.
Isn’t it time for the sale of goutweed to be banned in your area as well? That’s certainly something worth thinking about.