Invasive Plant Management

Jennifer NicholsField Notes

It’s a great time of year to be outside.  Temperatures and humidity are lower, and we don’t need to bundle up yet.

If you have taken this opportunity to stroll around your property and quickly became discouraged because it looks like a jungle out there, take heart. Fall and winter are a great time to regain control of invasive plants, and get a jump on managing them for next year.

Before I get too far into invasive management techniques, let’s define our terms. According to the USDA:

An “invasive species” is defined as a species that is…

  1. Non-native (or alien) to the ecosystem under consideration; and,
  2. Whose introduction causes or is likely to cause economic or environmental harm or harm to human health.

(The proper horticultural term for other plants that may become aggressive in the garden is “thugs”.)

Advantages to Fall & Winter Control

Easy Identification: Some plants are very easy to identify and locate in the winter. For instance, honeysuckle shrubs (Lonicera maackii, L. morrowii, and L. tatarica) are some of the last shrubs to drop leaves in fall. They produce red, shiny berries, while multiflora rose has green stems all winter which are easy to spot in wooded areas.

Easy Access: Impenetrable thickets become manageable after leaves drop, making access and removal much easier.

Taking Advantage of Plant Attributes: Some invasive plants, such as English Ivy (Hedera helix) remain evergreen while many native groundcover plants are dormant. This may be an opportunity to apply an herbicide to gain control of large infestations.

Better Pricing: You may be able to request special pricing for large winter projects if your landscape company is especially slow at this time of year.

Additional Tips

Know Your Invasive Plants: Just because you buy a plant at a garden center, doesn’t mean it isn’t invasive.  Believe it or not, plants such as Japanese barberry (Berberis thunbergii) are both on the PA invasive plant list and readily available for purchase.

One Species at a Time: On my own property, I often try to control one invasive species at a time. I find it easier to get rid of all Wineberry (Rubus phoenicolasius) for example, rather than every invasive plant on three acres. The additional benefit of this approach is that it is then easier to keep that species under control since it is no longer spreading from within the property lines.

Continued Maintenance: It may take several years to get control of an unwanted species if there is a seed bank present. Invasive plants will always re-establish themselves given the opportunity, so once you remove a species, keep it out by continued monitoring and control.

Minimize Disturbance: Disturbed soil is an opportunity for invasive plants to become established.  Make sure soil is covered with mulch and disturbed areas are monitored.

Timing is Important: If you can disrupt the life cycle of a species, you will be much more effective and reduce the amount of work required to gain control. For instance, bush honeysuckle’s berries ripen in the fall.  Removing the plant before this happens keeps these berries from becoming next year’s unwanted shrubs.

Fill Empty Spaces: The easiest way to keep invasive species out is to fill your property with desirable ones. Replace bush honeysuckle, burning bush, and multiflora rose with viburnums, rhododendrons, and bottlebrush buckeye. Replace Norway maples with Sugar maples or other native trees. This approach takes opportunities away from invasive species, and improves the ecological function of your property.

Although there is almost always something to do in the garden, fall and winter can be a bit slower. So take advantage of the season and use the cooler weather to manage invasive plants on your property.