How To Manage Invasive Plants

Invasive plants can quickly take over your garden, choking out native species and disrupting the local ecosystem. Identifying and removing these aggressive intruders maintains a healthy, thriving landscape. In the above video, This Old House expert Lee Gilliam showcases effective techniques for managing invasive plants and restoring balance to a homeowner’s garden. Learn more by reading our guide.

Identifying Invasive Species

Before tackling invasive plants, correctly identify them. Some common invasive species in residential landscapes include:

• Asian bittersweet
• English ivy (in some regions)
• Japanese knotweed
• Kudzu
• Purple loosestrife

While not all non-native plants are invasive, those that spread aggressively and outcompete native species can cause significant ecological damage. Gilliam identifies Asian bittersweet as a problematic invasive species in many landscapes due to its rapid spread and resilience in varied environments.

Pro Tip: Randall Prostak, an invasive-plants specialist at University of Massachusetts Extension, warns that the very traits that make a plant useful can make it dangerous: “What makes a plant a great ground cover can also make it a garden thug.” Before planting aggressive spreaders like English ivy, common periwinkle, or bugleweed, consider whether you can realistically keep them in check.

Distinguishing Between Invasive and Aggressive Native Plants

It’s important to note that not all problematic plants in your garden are invasive. Some native species can also grow aggressively and may require management. For example, English ivy is native to parts of New England but can become problematic if left unchecked.

When assessing your landscape, think about both invasive non-native species and aggressive native plants that may be causing issues. Understanding the characteristics and growth patterns of these plants can help you decide on the best strategies for control and removal.

Removal Techniques for Invasive Plants

Once you’ve identified invasive species in your garden, it’s time to take action. Below are several effective methods for removing these unwanted plants.

Manual Removal

When manually removing invasive plants, be thorough in extracting all parts of the plant, including roots and rhizomes, to prevent regrowth. Persistence is key in this process, as some species may require repeated efforts to fully eliminate. For smaller infestations or individual plants, manual removal can be an effective approach. This method involves:

1. Cutting back vines and aboveground growth.
2. Digging out roots using a garden fork or shovel.
3. Removing all plant material from the area to prevent regrowth.

Pro Tip: Roger Cook, This Old House landscape contractor, stresses the importance of getting to the roots during manual removal: “The more you can get up of the root system, the better off we’ll be.” He also advises against composting removed invasive plant material—instead, bag it and put it out with the trash. “I don’t want you composting it, or doing anything else with it, it’s a bad thing,” says Cook.

Chemical Control

In cases of large infestations or particularly stubborn species, chemical herbicides may be necessary. Use chemical control judiciously and as a last resort due to its potential impact on the surrounding ecosystem. Here are some steps to follow:

1. Choose herbicides specifically formulated for the invasive species you’re targeting.
2. Follow all label instructions carefully.
3. Apply herbicides during the plant’s active growing season for maximum effectiveness.
4. Hire a professional for large-scale applications or if you’re unsure about proper usage.

Pro Tip: Roger Cook, This Old House landscape contractor, recommends a targeted approach when invasive weeds are mixed in with desirable plants: “I like to cut the weed down to the ground and, as soon as it leafs out again, paint the chemical onto the leaves using a foam brush.” Coat all of its leaves, and it will finally die, roots and all.

Timing is critical when applying systemic herbicides. As This Old House landscape contractor Roger Cook has explained, spraying too late in the season—such as October—often fails because the plant is no longer actively growing. A systemic herbicide must be absorbed by the leaves and travel down through the trunk into the roots to kill the whole plant. If the plant isn’t actively growing, the herbicide may only reach the leaves without completing its journey to the root system, resulting in the infestation returning even larger the following spring.

Biological Control

You can manage some invasive plant species using biological control methods, such as introducing natural predators or pathogens. However, you should only implement this approach under the guidance of ecological experts to avoid unintended consequences.

Biological controls can provide a sustainable solution but require patience and precise execution to align with ecological standards. These methods often integrate with other control strategies to effectively manage invasive plant populations.

Preventing Future Plant Invasions

After removing invasive plants, take steps to prevent their return and the introduction of new invasive species. Use these preventive measures:

• Avoid using wildflower seed mixes that may contain invasive species.
• Clean gardening tools and equipment to prevent the spread of seeds or plant fragments.
• Educate neighbors about the importance of managing invasive plants to prevent their spread.
• Regularly monitor your property for signs of invasive plant growth.
• Research plants before adding them to your garden, opting for native species when possible.

Managing Trees Affected by Invasive Plant Species

Invasive vines and climbing plants can pose a significant threat to trees. Gilliam expresses concern about ivy growing up a tree, highlighting the need for timely intervention. Below is how to address this issue.

Assessing Tree Health

Before taking action, evaluate the overall health of the affected tree. In some cases, it may be necessary to consult an arborist. The arborist can:

• Determine if you can save the tree or if removal is necessary
• Identify any diseases or pest infestations
• Provide guidance on proper tree care and maintenance

Understanding a tree’s condition allows for accurate diagnosis and treatment. Professional insights can guide interventions to guarantee safety and environmental compatibility.

Pro Tip: Board-certified master arborist Tierson Boutte advises caution when pruning mature trees affected by invasive vines: “We want to go easy on it. We don’t want to deprive it of the valuable nutrients that it gets by turning sunlight into sugar, which is the main thing that plants do.” He notes that “it’s a little hard on these mature trees to take off too much foliage,” reinforcing the importance of a measured approach when intervening.

Removing Vines from Trees

Addressing the problem at its source, such as cutting vines at their roots, is the best approach. Following up with regular checks prevents reinfestation and potential damage to trees. If invasive vines are overtaking a tree, follow these steps to remove them:

1. Cut the vines at the base of the tree using pruning shears or a saw.
2. Remove a section of the vine (about 1–2 feet) to prevent regrowth.
3. Allow the remaining vines on the tree to die and fall off naturally.
4. Monitor the tree for any signs of new growth and remove it promptly.

Tree Removal and Replacement

In some cases, a tree may have too much damage or disease to save. If tree removal is necessary, do the following:

1. Hire a professional arborist to safely remove the tree.
2. Have the stump ground to prevent regrowth and allow for replanting.
3. Replace the removed tree with a native species that’s well-suited to your area.

Choosing a replacement tree that complements local flora helps restore ecological balance and bring longevity. Replacement should factor in the tree’s ecological role and visual appeal in landscaping.

Restoring the Landscape from Invasive Plants

After removing invasive plants and addressing affected trees, it’s time to restore your landscape. This process involves rejuvenating the soil and selecting the right plant species to reestablish a flourishing garden.

Soil Preparation

Prepare the soil for new plantings by:

• Adding organic matter to improve soil structure and fertility
• Removing any remaining roots or debris from invasive plants
• Testing the soil pH and adjusting if necessary

Choosing Native Plants

Select native plants that are well-adapted to your local climate and soil conditions. Native species offer several benefits:

• They’re less likely to become invasive or problematic
• They provide food and habitat for local wildlife
• They require less maintenance and water once established

Gilliam recommends planting PJM rhododendrons to replace the removed tree and provide privacy. Native plants foster resilience and sustainability in garden ecosystems.

Proper Planting Techniques

Implementing correct planting methods secures plant stability and promotes natural growth cycles. When installing new plants, follow these steps:

1. Dig a hole twice as wide as the plant’s root ball and as deep as the container.
2. Gently loosen the roots if they’re tightly bound.
3. Place the plant in the hole, making sure it’s at the same depth as it was in the container.
4. Backfill with soil, firming gently to eliminate air pockets.
5. Water thoroughly and apply a layer of mulch around the base of the plant.

Ongoing Maintenance for Invasive Plants

Managing invasive plants is an ongoing process that requires vigilance and regular maintenance. Incorporate these practices into your garden routine:

• Continue to educate yourself about invasive species in your area
• Maintain healthy soil and plant communities to resist invasion
• Regularly inspect your property for signs of invasive plant regrowth
• Remove any new invasive seedlings or sprouts immediately