Collecting roadside blooms can sprout chaos in your garden

Oh, what pretty flowers growing by the roadside! Maybe I should stop and get some of those for my garden!

“Don’t do it,” said Sharon Yiesla, plant knowledge specialist at The Morton Arboretum in Lisle. “There’s a good risk that you will bring home a big problem.”

Although some of the flowers growing along the edges of highways and in alleys are native wildflowers, such as goldenrod, many more are nonnative plants that will spread aggressively in the garden.

“If they reproduce freely enough to dominate in the roadside, they’re likely to out-compete many of your other plants,” Yiesla said. These seductive blooms also are often invasive plants that spread to disrupt ecosystems in natural areas. “If you grow them in your garden, you’re adding to that problem,” she said.

One risky plant is dame’s rocket (Hesperis matronalis), a biennial with showy flowers in shades of white to purple, which is often mistaken for garden phlox (Phlox paniculata). “Dame’s rocket spreads like crazy,” she said. “You’ll be fighting it forever.”

Common orange day lilies (Hemerocallis fulva) are often called “ditch lilies” because they seem to grow in every ditch and roadside. “They are incredibly tough and very hard to get rid of,” Yiesla said.

Roadside drainage ditches are a perfect nursery for invasive wetland plants, such as purple loosestrife (Lythrum salicaria), with its violet-colored flower spikes, and common reed (Phragmites Phragmites australis ssp. Australis), a tall grass with wind-tossed tassels of bloom. Both plants invade wetlands and choke out the native plants that native birds and other wildlife depend upon.

Alleys and vacant lots are as full of treacherous plants as roadsides. For example, creeping bellflower (Campanula rapunculoides), with attractive spikes of purple bell-like blooms, is shade-tolerant and reseeds freely. If transplanted into an urban garden, it produces armies of seedlings and can also sprout new plants from its spreading root system. “That’s what makes it a real nightmare,” Yiesla said.

You may admire the white-and-green-splotched foliage of Bishop’s goutweed (Aegopodium podagraria) and think you have a spot where you could use it as a shade-tolerant ground cover. “Ten years later, when you’re still trying to dig it up, you’ll be very sorry you transplanted it,” she said. It spreads not just through seeds but through creeping underground stems that are extremely hard to eliminate.

If you see a climbing vine with delicate purple flowers and red berries, don’t bring it home. It’s probably bittersweet nightshade (Solanum dulcamara), and all parts of the plant are poisonous. The berries are very tempting to children.

“Free plants can come with a heavy cost,” Yiesla said. Get your garden plants through trusted sources. Before you buy, research the plant’s characteristics so you know you aren’t buying a problem. “It’s a lot easier to avoid problem plants than to try and get rid of them,” she said.

For tree and plant advice, contact the Plant Clinic at The Morton Arboretum (630-719-2424, mortonarb.org/plant-clinic, or plantclinic@mortonarb.org). Beth Botts is a staff writer at the Arboretum.