Growing Zone 5-8
Rebecca Finneran is a garden expert, and even she was seduced by the rose campion.
Finneran, a senior horticulture educator with the Michigan State University Extension, planted the perennial, known for its gray foliage and magenta blooms, in her home garden.
But it had a mind of its own.
“I loved that plant. And I suddenly realized that it was coming up down the hill in the woods from my garden,” she says. “And I would faithfully go down there and dig it up and bring it back. And then I looked out one day and, holy mackerel, there’s hundreds of them.”
While the rose campion isn’t technically classified as invasive in Michigan, it’s a plant that can quickly spread, popping up in unwanted places or pushing out other native species. It’s a reminder to gardeners to be responsible for what they plant, Finneran says. That means, for example, avoiding true invasives, monitoring energetic spreaders or non-disease-resistant varieties, and managing plants that can be water hogs or fire risks.
“I think gardeners need to better observe what their plants do,” she says.
So while it might be love at first sight at the garden center, research whatever you plant to make sure you aren’t introducing a problem like one of the varieties of bamboo that have proven to be invasive in the United States. One of Finneran’s most important garden tools is her phone, which she uses to research cultivars before she buys them to see if they are plants not to plant. What should you be on the lookout for? Here are four categories to help you know:
For homeowners, super-spreaders like rose campion can be a pain, but invasives are a whole other level of headache. When plants like bush honeysuckle or Mexican petunia escape your garden and intrude on the natural landscape, they displace native species, threaten the ecosystem, affect fire patterns and even change the biochemistry of the soil, says Deah Lieurance, a member of the faculty at the University of Florida and chair of the Florida Invasive Species Council. Florida spends $45 million a year trying to clear conservation areas of invasive species, most of which have been introduced through horticulture, Lieurance says.
How do you know if a plant is invasive? County extension agents and master gardener programs have information, and many states have invasive plant councils that assess risks, says Lieurance. Some states, like Massachusetts, maintain a list of banned plants.
Last year, the Pennsylvania Department of Agriculture instituted a ban on nurseries and stores selling Bradford (or Callery) pear trees, loved by homeowners and builders for their fast growth and showy flowers. But the trees spread and crowd out other species, grow spurs that make walking through brush difficult, have long taproots that complicate removal and self-destruct after 15 or 20 years, says Theresa Culley, who heads the biological sciences department at the University of Cincinnati and works with Ohio’s Invasive Plants Council.
Not all non-native plants are invasive: It’s OK to grow something that doesn’t grow naturally in your area as long as it doesn’t pose a threat, Culley says. But do the research to find out which ones are safe.
- Water hogs
Depending on where you live or what drought conditions may be in effect, water may be scarce or expensive. It’s therefore strategic to look for plants that require little water or to group water-lovers like astilbe and ligularia in one area of your garden so heavy watering is limited to one spot, says Finneran, who writes about water-smart gardens for Michigan State. Here, too, it pays to research a plant to learn about its native habitat. For example, the red maple is popular with homeowners, but it’s also known as swamp maple, which says a lot about its water needs.
“In my world, we’re constantly diagnosing plant problems that we create ourselves because we have one uniform irrigation practice,” Finneran says. “We’re irrigating the plants that hate to be irrigated along with the plants that love to be irrigated.”
Also, consider where you place container plants. A container tomato will need more water if it sits in a heat-absorbing location like an exposed deck or a stone patio.
Look for plants that fit your conditions and what you can manage, Finneran suggests. “It’s really hard for the beginning gardener because the beginning gardener looks at a magazine and they go, ‘Oh, I want that.’ You just can’t have it all. It’s like buying clothes that don’t fit you.”
- Disease spreaders
Gardeners tend to design by shape or color, but Finneran advises that you factor in disease resistance or you risk having a weak cultivar that spreads a pathogen like powdery mildew throughout your flower bed.
“One of my favorite plants is tall phlox,” she says. “They’re fragrant, they’re colorful, but oh my gosh, some of them are really resistant to powdery mildew, and some of them are terrible.” Her solution? Removing susceptible cultivars from her flower beds and replacing them with varieties that are disease resistant.
“Keep in mind that the more disease you allow to be in the garden, the more disease you’ll have,” she says.
- Fire risks
This winter’s Marshall fire near Boulder, Colorado, which destroyed over 1,000 homes, is a tragic reminder of the increased risk of wildfires, says Christopher Jones, who’s responsible for agriculture and natural resources extension programs at the University of Arizona. The latest strategy for fire safety is to prevent wildfire embers from igniting materials — including plants — around a house, he says.
“Now they say no plants within zero to 5 feet of the structure, and we’re recommending that you use containers, things you can move out of the way in case of a fire,” he says.
Jones offers presentations on how to be fire wise, and several western state extension services distribute an ember awareness checklist. While no plant species is totally fireproof, deciduous plants tend to be the most fire resistant because the leaves have a high moisture content, he says. That’s opposed to plants that have mechanisms to retain moisture — including conifers, junipers and pines, and arborvitae. “They have needles or scales so they can hold that moisture,” he says. “That’s done because of the oils and resins that are in those needles. The presence of [those oils] just allows them to really burn hot.”
Aromatic plants are dangerous, Jones says, since it’s the oils that make them smell so good. Rosemary is one example. “Great, easy plant for us to grow around here,” Jones says, “but if it catches on fire, it’s going to burn very hot.”
Even a fire-wise plant can become a problem if it isn’t kept trimmed and free of detritus. “You want to keep them well maintained rather than allowing a lot of dead material to build up around them,” Jones says.
Fire risk is yet another reason to avoid invasive plants, Jones says. Buffel grass and red brome, for instance, are range grasses that were introduced into the West and have contributed to wildfires, he says.
For more information on how to protect yourself and your property, check with your extension service or fire department