10 Fast-Growing Plants You Should Never Grow in Your Garden, Say Horticulturists

Japanese Knotweed

It goes without saying that you should avoid growing invasive plants in your yard—and Japanese knotweed is at the very top of that list.

"It grows incredibly fast—up to several inches per day during peak season—and spreads via an extensive underground root system that can reach over 20 feet from the parent plant," says Tabar Gifford, master gardener and partnership cultivator at American Meadows.

Even worse, it's known to force its way through cracks in pavement and foundations, seriously damaging homes and landscaping. Since it can grow to be so tall and thick, it can also be exceedingly difficult to remove once established, so it's best never to plant this fast grower at all.

English Ivy

English ivy may look beautiful, but it can become a big problem if left unchecked. It can take just a few months to settle into a garden, according to Niki Jabbour, founder of Savvy Gardening. Once it's there, it can be hard to eradicate.

"It easily escapes gardens to spread in woodland areas," says Jabbour. "It also scrambles up trees and smothers the trunk and branches, impacting their health and lifespan."

Gifford adds that it can outcompete native vegetation, degrade wildlife habitat, and become extremely difficult to eradicate. However, many still use it as a ground cover—but there are better, less obtrusive alternatives.

Periwinkle

Periwinkle may look beautiful, but it's best kept away from your garden. "Don't let those glossy green leaves and purple blooms deceive you," says Jabbour. "This plant has a vining growth habit that easily escapes cultivated areas."

Gifford refers to it as a "long-term nuisance," noting that it roots wherever its trailing stems touch the soil, so it can smother surrounding plants and escape garden beds into woods and natural areas, where it will then outcompete native species.

Lily of the Valley

Lily of the valley is a bad idea for a few reasons. For one, it's invasive, and can spread its rhizomes quickly into natural areas. It's also very poisonous to humans and pets. Jabbour notes that it's an "old-fashioned perennial beloved for its super fragrant flowers," but it quickly expands "at the expense of nearby perennials." We'd recommend avoiding it altogether.

Mint

Mint grows and spreads incredibly quickly, and can take over your garden before you know it, smothering other plants so they can't properly grow. "I’ve seen it completely overwhelm herbs and perennials that were thriving before mint showed up," says Gifford. "Now, I always grow mint in containers."

So if you plan on growing mint for mojitos or teas, make sure to only grow it in a pot or container—or an herb spiral. Otherwise, it can quickly overtake your entire garden.

Goutweed

Many people use goutweed as a ground cover, but it's best not to plant this fast grower in your garden. It's very invasive and can quickly get out of control.

"It forms a dense blanket of green or variegated green-and-white leaves in sun or shade," says Jabbour. "The web of underground rhizomes spreads rapidly throughout garden beds, as well as lawns and other wild areas, where it chokes out other plants."

Keep your eyes peeled for goutweed—it may be hiding where you least expect it. "[Mine] came as a hitchhiker along with a hosta plant given to me by a neighbor. The lesson I learned? Be wary of accepting plants from other people's gardens," she adds.

Ribbon Grass

"This vigorous ornamental grass should come with a warning label," says Jabbour.

Ribbon grass is an extremely fast, aggressive grower that can become a real threat to natural areas and wetlands. It's typically used as a ground cover, and it has beautiful, green-and-white leaves. But don't let that fool you.

"Once established, it’s backbreaking work to remove the tangle of plants and roots," she adds.

Bamboo

"In a typical home landscape, bamboo is often more of a menace than a marvel," says Gifford.

Why is it so problematic? Many species of bamboo spread aggressively via underground rhizomes, she says, sending up roots far from the original planting site. This means the plants will quickly overtake garden beds and even damage hardscaping.

"If a gardener insists on growing bamboo, it's best confined to large containers or enclosed beds with professional-grade rhizome barriers installed," she says.

Russian Elm

A fast-growing tree may seem like a wonderful idea—but only in certain scenarios. Russian elm, for example, is best left out of your garden, according to Lauren Carvalho, horticultural manager at High Country Gardens.

"It's an invasive pest where I live," she says. "It grows to maturity in just 10 years, and often has brittle branches, resulting in dangerous deadwood."

Russian elm also spreads very aggressively, producing seeds that sprout into difficult-to-remove saplings. "The third strike is that it's a thirsty drinker, and hogs precipitation," she adds.

Purple Loosestrife

Purple loosestrife is "undeniably beautiful," says Gifford, with lovely purple blooms. However, it's also incredibly damaging to wetland areas.

"It spreads rapidly by seed and underground stems, forming dense colonies that crowd out native plants, such as cattails and sedges," she says. "These monocultures reduce biodiversity and degrade critical habitats for fish, birds, and amphibians."