4 Common Mistakes When Removing Invasive Plants

The #1 mistake I find people make when weeding or removing invasive plants is removing them but without putting anything in their place.

Invasive plants are there for a reason--they are well-adapted to grow in whatever conditions they thrive in.  If you have a particular plant that is invasive in your garden or in some particular area, you can be virtually assured that that plant is well-adapted to grow there, and, even if you remove all of it, it will probably quickly return if you remove it and leave the area vacant.  Many invasive plants have seeds that are widely distributed by wind, birds, or other animals, so the plants are going to end up in your area whether you want them to or not.

The best way to keep out unwanted weeds, in my experience, is to grow plants that also grow vigorously and can out-compete them.

For example, if you want to control Chinese pachysandra or lesser celandine, try planting plants like mayapple (shown below) which are native and grow taller than them.  Growing multiple plants is better--the more lush and diverse your community of native plants you have, the harder it will be for non-native plants to invade the area.

When weeding, people are often tempted to try to remove as much of a plant as they can, including the plant's full roots.  This desire has good reasoning behind it--if you leave part of a plant's roots in the soil, it can often resprout.

But trying to remove plants by the root can sometimes backfire.  If you pull plants up by the root, you can often bring a big clump of soil with them, as their roots cling to soil.  In some cases, you may even pull up other plants with them.  If you weed a large area at once, in such a manner, you can create a large area of exposed soil.

Exposed soil is easily washed away by heavy rain, and can also be parched and degraded by exposure to dry heat and sunlight.

In addition, many invasive plants thrive in disturbed soil and degraded ecosystems.  If you weed in such a way that leaves lots of exposed soil, you will most likely find a bunch of invasive plants sprouting up in the exposed dirt that you leave.  This is especially true when trying to control plants like mugwort, pictured below, which thrive on disturbed soil.

In order to minimize soil exposure and loss, I recommend the following measures:

• When effective, cut plants back to the ground without pulling them up.  This requires much less effort, and can be done considerably quicker than pulling up plants by the root.  This method is most effective (1) when the invasive plants are growing intermixed with other plants, which you do not cut, and (2) when done repeatedly.
• When pulling up a plant, place your foot next to the base of the stem of the plant you are pulling out.  This holds the soil down and will enable you to pull up a bare root and leave most of the soil in the ground.  The bare roots of the weed will ensure that the plant dies more quickly, as it is disconnected from the stores of water and nutrients in the soil, and more of the soil will remain in the ground for other plants to use.
• After pulling up a plant, if soil is still detached, knock off as much of the soil as possible, using your foot or a trowel or other tool, and put the soil back into the hole created by your pulling of the weed.
• If conducting large-scale weeding that leaves exposed soil, consider covering any exposed soil with a coarse mulch, in order to prevent soil loss or degradation due to heavy rain or exposure to sun.

Plants are time-sensitive life forms; they live on a schedule, sprouting, growing, flowering, going to seed, and going dormant at different times of year.  These features are most evident in temperate regions, and regions with seasonal rainfall, which includes nearly all of the U.S.

In order to control or remove a plant, knowing the timing of its lifecycle is critical to success.  Annuals sprout and then grow through a single season, putting all their resources into seed production before dying.  Perennials sprout from roots each year, investing early energy into producing leaves and stems, which they use to capture solar energy that is then stored in roots for future years, putting only a little energy into seed production each year.  Woody plants invest more energy in their physical structure, and are in it for the long haul.

Some common reasons weeding or control measures can fail include:

• Removing annual weeds too late, after they have gone to seed - Annual weeds die completely at the end of the growing season, after they set seed.  Cutting or removing a plant that has already gone to seed will not harm it at all--it may even help if your removal disturbs the seeds and distributes them over a wider area.  Some plants, like purslane, can store considerable water in their stems, and can use this water to go to seed even after you have cut or uprooted them.  For these plants, removing them early is even more important.  Each annual is timed differently; many sprout in spring and bloom in fall, but some have different timings, like winter annuals which sprout in late fall or winter, and may bloom as early as early spring.
• Cutting back perennial weeds too late in the growing season - This is ineffective, because the plant has had the whole growing season to store energy in its roots, and the plant was probably gearing up to go dormant anyway.  Late in the growing season, perennial herbaceous plants stop investing as much energy in their leaves and stems, and in autumn or before periods of dormancy, often begin breaking down their leaves in order to recycle some of the nutrients.  Cutting plants during this time will not do them much damage.

Usually, the best time to work on controlling weeds is during or directly after the most vigorous burst of growth.  For most plants, this is spring or early summer.  This times your control right after the plant has invested the most energy into growth, but before it has had the opportunity to extract much benefit from the leaves.  It also gives surrounding plants, which are likely still growing vigorously, an opportunity to utilize the sunlight and space freed up by removing the weedy plant.

For longer-lived woody plants like trees and shrubs, timing of control measures is less important, although still somewhat important.  Any time you cut or remove woody parts of a plant, you are causing it considerable harm.  A few fast-growing woody plants, however, like Ailanthus altissima, behave a little like perennial weeds, easily resprouting from underground roots.

I see a lot of gardeners expending huge amounts of effort trying to remove or control "weeds" when there is no need to do so, and when doing so may even be harmful to the ecosystem.

It is common for native plants, including wildflowers, shrubs, trees, and ground covers, to seed into your yard or garden and grow on their own.  In some cases, like a tree or shrub growing where it is unwanted, removing these is important.

But in many cases, the plants are causing no harm, and may actually be providing a benefit to the ecosystem, and adding additional beauty and biodiversity, such as when wildflowers or other annual or perennial herbaceous plants seed into empty space in a flower bed.  Native plants support native insects, which in turn support predatory insects and birds.  These animals higher-up on the food chain will help control insect pests that eat plants you grow, like food plants.

It is not natural for flower beds to have empty space and exposed soil or mulch; in a wild ecosystem, this space would fill up with plants, so as to utilize all available solar energy.  It is natural for plants to sprout from seed in this open space--with the exception of invasive plants, which are important to remove for practical and ecological reasons, you can see these volunteer plants as "free plants" that you can work with and use as a resource, rather than viewing them as weeds that need to be removed out of some vague sense of obligation to keep your garden orderly.

Some of the plants that I have seen come up from seed in people's yards in my region include:

• Jack-in-the-pulpit
• Black raspberry
• White and blue wood aster, panicled aster
• White snakeroot
• Great blue lobellia
• Black-eyed susan
• Goldenrod

Ironically, I've seen people pulling out these plants as "weeds" when many of them are for sale (and being actively purchased) elsewhere at nurseries and plant sales.

Some tips:

• Learn how to identify the plants in your yard and area - Get some books on plant ID, and perhaps get in touch with some people more knowledgeable about plants.  You can also benefit from browsing plants for sale in nurseries, seeing what the leaves look like so you can identify various fruits and flowers by the shape of their leaf alone.  This way you can quickly remove invasive plants, while retaining native wildflowers, and you can go out of your way when a particularly desirable plant or wildflower seeds into your yard.
• If a desirable plant comes up in a spot where you don't want it, move it or give it away. - Some plants, like jack-in-the pulpit, virginia bluebell, or the native wood poppy, can be prolific seeders and may come up in unexpected or unwanted places.  But these plants may be highly desired by some of your friends or neighbors, or you might even enjoy them if you move them to a different place.  Instead of just pulling these plants as weeds, try transplanting them or giving them away.