Ecological Control of Invasive Plant Species

| General

Controlling invasive plants may seem like a thankless task, but it is essential for the well-being of our ecosystems. The techniques and timing for eradicating weeds and invasive plants vary according to species. Conducting research, whether through online searches, reviewing gardening guides, or consulting with fellow gardeners, is crucial to find the best removal strategies for success. And it’s time well spent!

Simply removing invasive plants falls significantly short of what is required to heal our planet. It is only through the thoughtful restoration and re-establishment of native plant communities that we can foster a more resilient and thriving ecosystem.

While a weed is simply defined as an unwanted plant, invasive species are non-native to the ecosystem and their presence causes (or is likely to cause) environmental or economic harm or harm to human health. Invasive plants can disperse, establish, and spread without assistance or disturbance. Because of this, they are much more problematic in natural ecosystems than typical weeds. Read more about invasive plants.  

For managing the emergence of weeds and invasive plants, several strategies are available, each tailored to different types of plants and garden conditions. This brief overview touches on a range of physical techniques, from hand pulling and cutting to smothering and solarization, aimed at minimizing the impact of unwanted plants. However, it’s important to recognize that these methods represent just a sample of the myriad approaches to weed control.  

Hand Pulling: while this is the most labor-intensive method of weed control, it is one of the most effective methods as it removes the whole plant, including the roots. It is important to do this before a weed goes to seed to prevent future weeds from sprouting. Hand pulling of large weeds should be exercised with caution to prevent excessive soil disturbance and injury to the gardener. 

 Three smiling women are gardening together in a lush, native plant garden. One is kneeling and pulling weeds, another stands bending over the garden bed, and the third is standing by an educational signboard about native plants. They're surrounded by various flowering plants and a backdrop of trees and a bench, indicating a well-maintained community garden or educational setting. The atmosphere is casual and cheerful, highlighting volunteer community involvement in environmental education.
Wild Ones River City Chapter (Grand Rapids, MI) volunteers hand pulling weeds from a demonstration garden. Photo Credit: Wild Ones River City Chapter.

Cutting: for annual or biennial plants, cutting while blooming, but before going to seed, can be an effective method of control. Repeated cutting can also be an effective method of control for some perennial species.  

A group of seven cheerful volunteers equipped with gardening tools stands in a forested area, ready to engage in environmental conservation activities.
Wild Ones Oak Openings Region Chapter (NW Ohio & SE Michigan) volunteers preparing for invasive plant removal at a stewardship event.  Photo Credit: Wild Ones Oak Openings Region Chapter website.

Smothering: Great for controlling weeds in a large area, covering soil with materials such as mulch, newspaper or cardboard is often effective. 

A newly established no-dig garden bed on a grassy field, with cardboard laid down to suppress grass and weeds, topped with a layer of mulch. The garden bed is bordered by bricks and stones, with metal poles marking its perimeter, possibly in preparation for a fence to protect the area. The background features a pastoral landscape with a silo and farm buildings in the distance. The image illustrates an eco-friendly method of creating a garden bed without tilling the soil, preserving soil structure and microorganisms.
Site preparation at a Seeds for Education grant-funded garden site in Ephrata, PA. Students and staff outlined the space and placed cardboard, rocks, and much over the area to smother the turfgrass. Photo Credit: Hinkletown Mennonite School

Solarization: Covering the soil with clear plastic over an extended period to kill weed seeds in the top “baked” layer of soil. Using plastic is less environmentally friendly than other methods. Applying transparent plastic to moist beds for short periods of time forces weed seeds in the top layer of soil to germinate; those seedling weeds can be easily pulled or hoed. Repeating this process can deplete the weed seed bank in the top layer of soil, reducing the garden’s future weed pressure.  

A garden site in the process of solarization, with a black plastic tarp spread across a trench to trap solar heat and eradicate weeds, pests, and soil pathogens. This preparation step is essential for creating a healthy garden bed. The site is adjacent to a blue metal-clad barn, and the area is bordered with old wooden beams and concrete blocks to secure the tarp in place. A small amount of snow in the background suggests this is being done in cooler seasons when the sun’s warmth is harnessed for soil treatment.
Black plastic weighted down to solarize a patch of turf grass on a future native plant bed on a farm in central Wisconsin. Photo Credit: Crystal H., Green Bay Chapter.

Cultivation: This can be an effective way to control a large area of weeds while also loosening the soil for planting. The downside to cultivation is the increased potential for soil erosion and the disturbance and destruction of the underground microbial community that plays a vital role in ecosystem health. 

A person engaging in the act of cultivation as a method of weed control. They are using a garden fork to till the soil, which can disrupt weed growth by uprooting them before they become established. Cultivation not only helps to control weeds but also aerates the soil, facilitating the growth of desired plants. This traditional and manual technique is environmentally friendly and reduces the need for chemical herbicides.
A woman prepares the soil at a cacus farm using a garden fork. The process of cultivating the soil helps to remove unwanted plants and hinder weed germination and growth. Photo Credit: Getty Images.

It is important to note that the effectiveness of these methods vary depending on the specific weed species, the size of the infestation, and the surrounding environment. Planting a dense native hedgerow upwind of a garden can reduce the volume of weeds seeds that blow into a space. Integrated weed management, combining several of these methods, is often the most successful approach.  

 An informative diagram titled "Integrated Weed Management" showcases a multi-faceted approach to managing invasive plants, weeds, and pests to promote native landscapes. Four distinct strategies are interconnected: Ecological (cultural) practices are symbolized by a group of flowers with a butterfly, This method often employs planting to outcompete weeds, adding native hedgerows, etc. 
Physical (mechanical) methods by a shovel and plant, with techniques highlighted throughout this blog text. Biological control by an insect on a leaf. Biological control often employs the intentional introduction of non-native natural enemies for permanent establishment and long-term control of invasive species in the infested areas. Chemical (herbicides) by a spray bottle and dying weeds. Arrows flow towards a central concept, "Native Landscapes,"  illustrating the goal of replacing noxious weeds with native flora.
Integrated weed management is a multifaceted, ecosystem-based approach to managing invasive plants, weeds, and pests. This blog mainly discusses physical management techniques. Ecological weed management involves techniques such as varying planting density to “outcompete” invasive or undesired plants. Biological control is the intentional introduction of natural enemies (insects, mites and pathogens) of a target weed.

Chemical Control: Depending on the specific challenges and characteristics of your garden, targeted chemical control may be necessary. If you must resort to herbicide use, first research the efficacy and appropriate timing and methods for applications to target specific species.  and recommendations through your state’s Department of Agriculture and the Environmental Protection Agency. Ensure you wear the right protective gear and understand the risks, as many methods of chemical control can have detrimental impacts to watersheds, ecosystems, and human health. Herbicide training and certification programs are available in all states. Also, consider the potential for drift to affect both your garden and neighboring properties, which could lead to significant fines in some states. Never apply herbicides on a windy day. 

We recommend that people connect with fellow gardeners through their local Wild Ones Chapter to tap into shared knowledge and regional expertise. Connecting with others who have similar situations and local experts will make controlling weeds easier.

It’s important to note that simply removing invasive plants falls significantly short of what is required to heal our planet. It is only through the thoughtful restoration and re-establishment of native plant communities that we can foster a more resilient and thriving ecosystem. We must replace invasive plants with native plants to grow a healthier planet.