How to Fight Plants With Plants: Controlling Garden Nuisances

Proper plant selection and invasive removal are the keys to success. You must knock back the populations of invasives before inserting the new natives in their place, giving the desirable plants an opportunity to take over. 

Regionally-Specific Examples

For example, you could mow down quackgrass or Japanese stilt grass to the lowest level possible, then manually remove as much grass as possible. You could even use a tarp! Finally, plant fern plugs throughout the patch. The ferns will already have an advantage in a shady area. They may be able to grow fast enough that they shade out the grass and prevent it from resprouting.

Due to the massive diversity of invasive plants and environments, there is no tried-and-true recipe for success in this realm. Instead, experimentation is necessary. Observation is your most useful tool; if you notice a indigenous plant thriving and overgrowing vacant areas near your property, take the time to identify it and consider if it can outcompete the invasives on your land. 

Choose Prolific Native Plants and Beneficial Self-Seeders

Just because a plant is native does not always mean it is subdued. Some endemic species are prolific self-seeders, which means they spread thousands of seeds per plant to rapidly colonize new areas. Other natives spread quickly underground via rhizomes or runners.

These fast-growing indigenous species can take over fields, forests, roadsides, and gardens with little help from humans. Fortunately, local ecosystems are adapted to these wild plants. Their spread can support wildlife and improve soils without disrupting the natural order.

Better yet, we can use these ultra-strong natives in our fight against invasives. When you plant prolific natives, you have a better chance of smothering and overgrowing their invasive rivals. 

Key Caveat: As always, be sure to choose wildflowers, grasses, and shrubs that are specifically local to you. Some of these grow throughout the United States, while others should be kept in certain regions.

Never assume that you can grow a species just because a plant is native to the U.S. Some species, like jewelweed (Impatiens capensis), is native to the East and Northern U.S. but potentially invasive noxious weeds in the Pacific Northwest and Maine.

Shade Them Out

Too much shade is a big issue for vegetable gardeners, but it can be a major advantage for fighting invasive species. All plants require sunlight to photosynthesize, but some of them cannot handle too much shade. 

When you’re fighting full-sun grasses like Johnson grass (Sorghum halepense), taller shrubs and trees can help smother the grassy clumps with shade. Incorporate dense native shrubs like dogwood (Cornus spp.) or thick-foliage trees like Bigleaf maple (Acer macrophyllum) to prevent the sun from reaching the invasive grass. Better yet, as deciduous species drop their foliage in the fall, the leaves can act as a mulch to help smother the grass below.

On the flip side, some invasive grasses, like Japanese stilt grass (Microstegium vimineum), prefer partial to full shade. A great way to counteract this plant could be pruning back shrubs and taller-growing plants to expose them to the sun. Then, use a tarp to smother the remaining weeds and seed a bunch of sun-loving natives like black-eyed Susan to overgrow the area.

Preventative Planting

Many of the techniques we’ve discussed are offensive, meaning you are actively attacking an invader. But what about prevention? Some can be grown along the margins of your landscape to offer long-lasting solutions that hold their ground against any invasives that try to sneak in.

One popular preventative plant is black walnut (Juglans nigra). Widely known for its allelopathic properties, these trees are extremely effective at killing their neighbors. You certainly don’t want a black walnut near your garden, but it could be very helpful on the border of your landscape. Very few plants can handle the juglone compound released by black walnut roots. These powerful trees are like the linebackers of invasive defense.

Aggressive hedgerows are another preventative strategy. You can employ native shrubs and grasses to border your garden, preventing outsiders from creeping in. Southeastern wild rye (Elymus glabriflorus) is a particularly robust clump-forming grass used in the Northeast to keep invasives at bay. 

Dense clumps of beautiful native bee balm (Monarda spp.) and elderberry (Sambucus spp.) are robust enough to potentially kick Himalayan blackberries and bindweed to the curb. Even hardy wild grapes like Vitis californica offer a potential preventative strategy against English ivy and Japanese honeysuckle.

Prioritize Ground Cover (Never Leave Bare Soil)

Vacant, bare soil is like an invitation for invasives. Mother Nature prefers to keep her fragile “skin” (soil) covered, and whenever it becomes exposed, fast-growing, weedy plants tend to colonize the bare ground. 

This is why invasives are so prolific along roadsides, degraded farmland, and abandoned fields. But if you keep the soil covered with healthy native ground cover, weeds are less likely to invade the area because the ground is already occupied.

Ground cover describes any low-growing plant that rapidly covers an area with green carpet-like growth. Many ground covers are very useful lawn replacements. Others can be used for pathways between raised beds and garden borders because they aren’t tall enough to reach into the beds where crops grow. 

If you have a problem with invasive grasses or bindweed, consider using a ground cover plant to protect the bare soil from invasion.

Native Ground Cover Ideas

Selfheal (Prunella spp.) is a perfect example of a highly vigorous (sometimes weedy) endemic species that can outcompete invasive grasses. Fortunately, selfheal is very low-growing and produces flowers that magnetize bees. They grow in even the worst soil, sometimes popping up between concrete cracks. This plant is also highly resistant to foot traffic, making it the perfect alternative to non-native grasses.

Wild strawberries (Fragaria virginiana) are another groundcover that can be surprisingly effective. Some gardeners plant these low-growing alpine berries to outcompete garlic mustard and other weeds.

As a bonus, the tiny strawberries are very flavorful for humans and attractive to wildlife. Because the strawberries retain their foliage through the winter, they can often get a stronghold over the garlic mustard seeds before new seedlings sprout in the spring.

Replace Invasives With Native Equivalents

Sometimes, you have to turn family members against each other (hopefully only in the garden). Invasive species like Chinese wisteria (Wisteria sinensis) are extremely harmful to local ecosystems, but their relatives, American wisteria (W. frutescens), are actually native to North America. American wisteria can sometimes out-compete the ultra-aggressive Chinese cousin if it gets a head start. Fortunately, it also poses less risk of escaping your landscape and harming the surrounding environment. 

Ideally, invasive wisteria varieties wouldn’t even be available for purchase at nurseries, so we could avoid these problems from the beginning. But if a Chinese wisteria has started to spread, consider pruning it back or ripping it out and planting a vigorous American wisteria nearby to overgrow it. The American wisteria is more of a shrub, so a large specimen could overgrow a cut-back Chinese vine.

To give your native allies the best chance at success, destroy the invader as much as possible before replanting. You can rip it out, mow it, cut it, tarp it, or, in extreme cases, spray it with strong horticultural vinegar, which is still safe for organic gardens. Always be sure to wear protective gear when applying any chemical, as even concentrated vinegar can be potentially dangerous to your eyes and skin!

Consult your local extension office for the best methods and timing for removing specific invasive species. Some are highly resistant to pulling at certain growth stages. 

Redefining Our View of Invasives

In books like Beyond the War on Invasive Species and The New Wild: Why Invasive Species Will Be Nature’s Salvation, authors suggest that aggressive chemical or mechanical attacks on invasive species are actually doing more harm to ecosystems than good. Instead, they offer a perspective-shifting view that some invasive plants can be used to help our local grasslands and forests move toward ecological succession. 

In other words, we don’t necessarily need to spray all the invasives in chemicals to “win” the fight. We could listen to what nature is trying to tell us about these ecosystems. For example, massive overgrowths of kudzu vine in the South or Scotch broom on the West Coast may be signs that these ecosystems want to return to native forests with robust stands of trees.

The bare, disturbed ground is often the first invitation for invasive species to take hold. If we keep the soil protected and stop deforestation of tree-filled areas, we could help restore balance instead of fighting to bend nature to our own desires.

I am not saying that Epic Gardening agrees with all the statements in these books. Instead, I suggest that we look at some invasive species in a new light, particularly those that provide positive benefits to pollinators or wildlife. While we clearly don’t want invasive species to overtake our gardens and landscapes, some simply won’t go away. Is spraying them or mechanically removing them plausible forever? Probably not. 

For now, let’s see if we can fight plants with plants and use our workhorse native allies to outcompete the invaders!