Taming the Beast: How New Plant Cultivars Combat Invasive Spread

Breathe Easy, Plant Smart

First, take a breath. Planning and planting a garden should be a delight, not a dilemma. And while you’re right to avoid invasive plants, it’s also important to understand exactly what an invasive plant is—and more importantly, whether or not it’s invasive in your area.

“The Vine That Ate the South.”

Did the horror stories of kudzu introduce you to the term “invasive plant”? Or perhaps Japanese privet and its wide-ranging spread enticed you to rethink what shrubs to use as a privacy hedge. Or maybe you’ve seen the rampant reproduction of Bradford pears, those malodorous, weak, easily damaged trees, popping up in open fields.

Whatever plants introduced you to the headache of invasive plant species, it’s good to be aware of their implications—but it’s also important to realize that not all plants labeled invasive invade all USDA zones. Some plants are worse than others, with widespread bullying tendencies. But plants that may be considered invasive in USDA zone 10 may never spread in chilly zone 4.

The phrase “right plant, right place” should always guide your garden choices.

But what, exactly, defines an invasive plant?

An invasive plant is an aggressive, non-native species whose presence causes environmental or economic harm. Invasive plants grow and reproduce rapidly. Approximately 42 percent of threatened or endangered species are at risk due to non-native, invasive species—which include not only plants but also animals and other living organisms, such as microbes.  Invasive plants compete with native species for water, light, nutrients, and space. They can out-compete native plant communities and degrade wildlife habitats. Many states ban invasive plants due to the harm they cause to local ecosystems. You can find which plants to avoid in your garden here.

Invasive Versus Aggressive Plants

Native Plants

Native plants occur within a region as the result of natural processes and are adapted to local climate and soils. If the species was present before widespread European settlement, it’s considered a native plant.

These plants co-evolved with native insects and wildlife, making them critical to ecosystems. While some gardeners consider them troublesome weeds, many of these aggressive native plants help prevent erosion along riverbanks, provide nectar for pollinators, serve as a food source for caterpillars, and feed birds, both with their seeds and by attracting insects beloved by our feathered friends. While aggressive native plants may irritate gardeners who prefer tidy, perfectly manicured beds and borders, these plants provide benefits that many non-native invasive species don’t.

Non-Native Plants

Non-native English ivy, mahonia, nandina, lantana, buddleia, spirea, Japanese barberry, Asian beautyberry, and privet, among others, find themselves listed as invasive species in some parts of North America. If you find these plants in your garden—don’t panic. Many landscape designers and home builders included these non-natives because they grow quickly, bloom profusely, and look good, only to discover their wayward ways much later.

How To Outsmart Invasive and Aggressive Plants with These Gentle Maneuvers

If you discover aggressive or invasive plants in your garden—but don’t want to rip out and recreate your established beds—consider a little TLC to keep the plants in check.

• Deadhead flowers after blooming to prevent seeds from spreading.
• Mulch areas around the plants to reduce the number of seeds that germinate, as they need direct contact with soil to grow.
• Remove seedlings early when they’re easier to pull up.
• Prune suckering plants to contain their growth so they don’t outcompete other plants for light and nutrients.
• Dig and remove offshoots or runners to keep the plant’s growth in check.
• Replace invasive plants with sterile cultivars.

If your state lists a plant as invasive, follow the state guidelines.

Remove the plant if it’s banned, and look for an alternative, like a sterile cultivar, for plants you love.

New Plant Cultivars: The Secret Weapon in the Fight Against Invasive Species

How Plant Scientists Are Rewriting the Invasive Species Story!

Many National Garden Bureau members offer new, sterile cultivars of plant species deemed invasive or aggressive. Sterile is defined as producing no or few seeds but nectar production is not negatively impacted. This allows you to enjoy the flowers and foliage in your garden—without fear of decimating your local ecosystem.

The Bradford Pear Conundrum…

In the past, “sterile” cultivars may not have been self-fertile, like the Bradford pear, but some plants still cross-pollinated with wild species. For instance, Bradford pears easily hybridized with other Pyrus calleryana cultivars, as well as P. betulifolia, also known as Asian pears, producing fertile fruit—and filling fields with invasive seedling forests.

New breeding efforts ensure that sterile cultivars don’t cross-pollinate and spread. These stringent requirements resulted in inter-specific hybrids that don’t face the same restrictions in states where an invasive species is banned.

Hybrids can be sold in these states if they’ve been trialed and shown to produce less than two percent viable seed, often referred to as “low seed set.”

Good News for Butterfly Lovers: Enjoy the Year of the Buddleia Without Worries

So, if you love watching butterflies and hummingbirds flit among the flowers of buddleia in your garden but worry about its invasive ways, consider celebrating the Year of the Buddleia with new, sterile cultivars from NGB members. Here are a few series to look for.

Ideal for patio containers, window boxes, and even hanging baskets, this compact buddleia produces an excellent mounding habit—as well as a very low seed set. Available in White, Cranberry, Blue, Pink and Purple. Hardy in USDA zones 5a-9a.

Love Nandina? Sterile Cultivars for Heat-Loving, Eco-Conscious Landscapes

But buddleia isn’t the only sterile cultivar of well-loved—but sometimes invasive—plants. Nandina, an attractive heat- and drought-tolerant evergreen shrub known for its pretty foliage, spreads invasively in southern climates due to its prolific fruit. The fruit contains cyanide compounds, making it toxic to wildlife–especially for cedar waxwings, who ingest large quantities of it. While vigilant gardeners can prune off the fruit to avoid its spread, instead consider the colorful, sterile new cultivars available like:

Safe and Sustainable Privets for Landscaping with No Invasion

Along with Buddleia and Nandina, both Chinese and Japanese privet finds itself on many states’ invasive species lists. Fortunately, a sterile species provides the same benefits beloved by landscapers and gardeners without the invasive tendencies like this new plant.

With the features that made the privet a favorite of landscapers, the rounded, upright habit, glossy evergreen foliage, and white fragrant flowers looks lovely in the garden—but exhibits no female fertility.

The classic hedge is well-behaved and seedless, producing lightly fragrant flowers in the spring to summer. Plus, like conventional privet, this new cultivar is deer resistant, as well as drought and heat tolerant. Hardy to USDA zone 7.

A classic landscape addition with a twist: this spectacular spirea produces no seeds, so you can plant it without fear of invading your neighbors’ gardens! Not only is it sterile, it produces gorgeous early spring red foliage, followed by bright, purple-red flowers in late spring…and all summer long.

Because it doesn’t produce seeds, the plant puts all of its energy into flowering, meaning you’ll enjoy a non-stop show all season. This beauty also makes your life easy, because it’s drought tolerant, deer resistant, and needs no deadheading to reflower. Hardy in USDA zones 3 to 8.