Thug plants to avoid in the landscape

Story and Photography by Susan Albert

Everyone who gardens can relate to the oft-used phrase “garden thugs.” During the experimental stage, when early gardeners eagerly try many plants with wild abandon, they may come across some decidedly ornery plants that cause extra work removing their offspring. And while some thugs may possess desirable attributes – such as fragrant flowers or nectar for pollinators – chances are good that a less aggressive plant could be substituted. 

Jackmanii is a classic clematis.

Below are five ornamental plants that, when left to their own devices, will reproduce by rhizomes, seeds, bird droppings (ate the seeds), or a combination of these. Fastidious gardeners who don’t mind the extra work of constantly cutting back or digging up these plants may enjoy their presence, but for the rest of us, choose another plant. 

Sweet autumn clematis (C. terniflora)
This innocent looking, fragrant splash of small, white flowers draped across a fence may be enchanting the first year or two, but then turns evil as its seeds take root and vines climb every shrub in the yard. Even the lawn is not immune or your favorite perennials. The twisting vine crawls, climbs, and clings to everything in its path.

Garden space is prime real estate, so be careful when choosing new additions, and if they take on a bullying personality, it might be time to give them the heave-ho.

The voluminous amount of seeds become too tedious to trim each fall, hence the rapid reproduction. To tame this thug, cut the vines to the ground after flowering in the fall to remove the seeds and the prolific foliage. For a more permanent solution, dig up or treat the vines with glyphosate, but it may take years to eradicate it.

Alternative – Choose a large-flowered Clematis that is more well behaved, such as the classic violet Jackmanii clematis (Clematis x jackmanii) or the pink C. ‘Nelly Moser’ (Zones 4-8). Clematis comes in a wide array of colors and varieties. Different Clematis groups should be pruned at different times to maintain size. Group 1 blooms on last year’s growth and should be pruned after it flowers in the spring. Group 2 blooms on old and new growth so it really doesn’t need much in the way of pruning. Group 3 blooms on new growth only, so it can be pruned hard in late spring or fall if needed.  

Left to right: 1. Sweet autumn clematis weighs down a Viburnum shrub. 2. Sweet autumn clematis looks pretty and is very fragrant. However, its growth is so prolific it is necessary to prune all vines after flowering to prevent seeding. 3. Sweet autumn clematis is a vigorous grower and will reproduce quickly from seed if allowed to remain on the vines.

Pipevine (Aristolochia tomentosa)
With its green, heart-shaped sturdy leaves and interesting “pipes” for flowers, the perennial Dutchman’s pipe or pipevine (Zones 5-8) makes an attractive backdrop on a trellis. It’s the food plant for the pipevine swallowtail butterfly caterpillars, a bonus that brings lots of butterflies to the yard.

It is slow to establish, but when it does, look out. It suckers underground and new plants emerge several feet away, climbing up nearby vegetation with a choke-like hold. The new growth can be untangled from the perennials and pulled up, but new runners are always on the way. It can climb a rain gutter downspout, flourish in cement cracks, and take over any nearby trellises.

Alternative – It may be wise to plant pipevine in a large pot submerged underground so it can’t tunnel out. Or surround it on all sides, below ground, with a deep barrier. However, that still may offer an escape route. You can also isolate it in a corner of the yard, where emerging runners won’t threaten other plants.

Left to right: 1. Pipevine climbs up this Knock Out rose. Pipevine reproduces through underground runners and can take over a garden bed. 2. Pipevine produces flowers reminiscent of smoking pipes. 3. Cracks and crevices are no match for pipevine.

Trumpet creeper (Campsis radicans)
Clusters of orange trumpet-shaped flowers are a favorite of hummingbirds but that is no excuse to plant this aggressive native perennial vine. Plenty of other nectar plants and vines will satiate the hummers. Trumpet creeper reproduces by seed and suckers underground, emerging everywhere. And it is difficult to pull up. The job requires a shovel or other tool for digging. 

Trumpet creeper could work in a large yard or in a country setting, but gardeners with small urban yards may rue the day they planted trumpet creeper. Some industrious gardeners manage to contain it in the center of the yard where they can mow all around it, cutting off the emerging runners. Reportedly, hybrids such as Campsis x tagliabuana ‘Madame Galen’ are almost as aggressive.  

Alternative – Plant another hummingbird attractant, such as coral or trumpet honeysuckle (Lonicera sempervirens, Zones 4-9). Trumpet honeysuckle blooms spring to fall and if left uncut, it will get heavy, but is not aggressive. A good shearing in late winter should keep it in check. Hummingbirds will relish their find all summer.

Another alternative is the native perennial crossvine (Bignonia capreolata, Zones 5-9), which sports a profusion of trumpet-shaped orange red flowers in spring. It is in the same family as trumpet creeper but is not as aggressive. If needed, it can be pruned after spring flowering.

Left to right: 1. The trumpet-shaped flowers peer out from a tangle of vines. Hummingbirds are attracted to its nectar, but the vines reproduce by rhizomes and may not be a good choice for a small garden. 2. The hummingbird favorite, trumpet honeysuckle blooms from spring to fall and is much better behaved than trumpet creeper. 3. Crossvine is another alternative to trumpet creeper.

Common goldenrod (Solidago spp.)
Even though goldenrod suffers with its oft-mistaken identity with the pollen-bearing ragweed, goldenrod multiplies rapidly from seed and underground runners. Its virtues include being a late summer bloomer that offers nectar for pollinators and a golden display of flowers when a lot of other plants are spent. 

Alternative – Many goldenrod cultivars are much better contained that the species. S. rugosa ‘Fireworks’ (Zones 4-8) increases in clump size but doesn’t tend to travel across the yard. 

Allow plenty of space for black-eyed Susan in the garden or it will roll right over nearby vegetation.

Black-eyed Susan (Rudbeckia hirta)
This hardy native boasts an explosion of blooms over a long bloom period and it also can be effective for erosion control. However, it spreads quickly by its fibrous roots and by reseeding, thereby jeopardizing neighboring plants. It is not easy to pull out; it must be dug up or sprayed with glyphosate. Black-eyed Susan consistently shows up on lists of butterfly-attracting plants, but plenty of other flowers will do the trick. 

Alternative – Purple coneflower (Echinacea purpurea, Zones 3-8) attracts butterflies, goldfinches, hummingbirds, bees, and other pollinators. It spreads easily by seed but doesn’t form a dense mat like black-eyed Susan that crowds out other plants. 

Talk among garden friends and you will discover many more potential thugs in the garden. Sometimes, the thugs are disguised as “plants shared with love” from an unwitting neighbor or friend. Most of us are guilty of passing along a favorite thug, such as old-fashioned Phlox or Monarda.

Garden space is prime real estate, so be careful when choosing new additions, and if they take on a bullying personality, it might be time to give them the heave-ho.

‘Fireworks’ goldenrod may be a better choice than the common species.

Caution: More Thugs Ahead
Here are more plants that lean toward the bully list for their aggressive behavior. To slow them down, try planting them in containers. Isolating the offending plants among hardscape such as walkways, walls, and patios can slow those with escaping rhizomes. 

Obedient plant (Physostegia virginiana, Zones 3-9): Species plant spreads quickly by underground runners and seeds. 

Mexican petunia (Ruellia simplex, Zones 8-10): A sterile variety is available, but it still spreads by rhizomes. 

Iris ‘Black Gamecock’ (Zones 4-9): Multiplies rapidly. 

Horsetail (Equisetum hyemale, Zones 4-9): Reproduces by spores and underground branching rhizomes. Best in container. 

Bradford pear (Pyrus calleryana ‘Bradford’, Zones 5-9): Weak branch structure and aggressive cross-pollinator.

Purple coneflower reproduces readily from seed, but not aggressively so. It is a good alternative to black-eyed Susan.
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