What is scary? Things that go bump in the night if you’re eight, urban blight if you’re a city dweller in the crosshairs of a developer and I think we can all agree on global warming, food contamination, and our diminishing resources as serious causes worthy of concern. But for most gardeners, scary is the sight of an innocent-looking plant with a cleanly variegated leaf in white and green springing from a succulent white root. In an informal survey of gardeners this spring, bishop’s weed, Aegopodium podagraria ‘Variegatum’ was the plant most often mentioned that people regret introducing to their planting beds.

Most of us received a start of this “wolf-in-sheep’s-clothing” from a kindly neighbor (red flag #1). What’s not to like? Bishop’s weed, sometimes referred to as goutweed, is tolerant of dry shade and difficult growing conditions, lighting up dark areas beneath shrubs and clothing the ground with its fresh foliage throughout the growing season, furnishing a clean skirt to emerging spring bulbs. Later, it knits together compositions of shade garden plants throughout the summer into fall when it quietly goes dormant with the first frost. But heaven help you if you decide this seemingly innocent plant—named for a man of the cloth, no less—is right for you. A more wickedly persistent and pernicious garden occupant you will never find. Its brittle roots insinuate themselves deep into existing clumps of plants, under rocks and apparently to Hades itself, so reliable is its appearance each spring in spite of all efforts to the contrary. No amount of constant weeding, grubbing out, cutting back and yes, even applications of glyphosate (Roundup®) seem capable of eradicating this simple, delicate-looking pest.

What constitutes a “scary” plant? While poets might posit that a weed is simply a plant in the wrong location or one whose best features are not yet recognized, some plants have developed amazing reproductive capabilities and remarkably tough constitutions that ensure their survival under frighteningly harsh conditions. Whether it is tough, resilient energy stores, aggressive root runs, or rapacious seeding capabilities the following plants are truly scary. Gardeners beware!

1. Bishop’s weed, Aegopodium podagraria—root run. (see above)

2. Toad flax, Linaria purpurea—seed. Delicate in appearance with bushy, upright stems clothed in narrow blue-green leaves, topped by tiny snapdragon-like blossoms. L. ‘Natalie’ is a sterile cultivar and a far better choice for the civilized garden.

Other notorious seeders

Brazilian vervain, Verbena bonariensis—seed. Tall branched wiry stems to four feet are topped by lavender umbels; a beautiful plant with a summer-long flowering period. Bad news—seeds freely; good news —individual plants are short-lived.

Pheasant grass, Anamanthele lessoniana and Mexican hair grass, Nasella tenuissima are both some of my favorite ornamental grasses with bronzy-orange and blond tresses respectively. Their narrow leaves and relatively short (two feet) mounding forms animate the wind, reflect the light and blend beautifully with shrubs and perennials in sunny, well-drained soil. They do, however, seed prolifically—but hey, you’re going to weed something out and it might as well be lovely.

Roots and runners

3. Montbretia, Crocosmia x crocosmiiflora—storage root/corm. “A favorite for generations” according to the new Sunset Western Garden Book, probably because gardeners have yet to find a way to control this colorful summer bloomer with its sword-shaped leaves and branched stems of fiery orange flowers.

4. Jupiter’s beard, Centranthus ruber
—seed and root run. A cottage garden favorite (another red flag) with bushy blue-green leaves and stems that produce a long season of small clusters of crimson flowers…and then seeds into every nook and cranny unless faded blossoms are religiously removed. A resilient and persistent taproot further insures its permanent place in the garden.

5. Ranunculus repens ‘Buttered Popcorn’—root run. An admittedly beautiful golden leaved form of a common creeping weed tarted up with a given (and tasty) name. A buttercup is a buttercup, I don’t care what color the foliage is!

6. Peruvian lily, Alstroemeria aurantiaca—root run. This species, not to be confused with its more well-bred kin, produces lank foliage of a mid-green color and funnel-shaped blossoms in brash hot colors. Vigorously spreading tuberous roots, while brittle and “frail” are tenacious and go deep —very, very deep—making this plant nearly impossible to remove. Learn to love orange cut flowers.

7. Houttuynia cordata ‘Chameleon’ —root run. A colleague fondly refers to this one as “horsetail in a skirt!” Rapidly spreading underground stems colonize wet ground, or even not-so-wet ground sending up heart-shaped green leaves splashed with cream, yellow, pink and red that smell of orange peel or dog’s breath depending on who you ask. While not garden-worthy, this is a lovely container plant in a water garden setting.

8. Spurge, Euphorbia species. In a family as vast and multifaceted as Euphorbiaceae there’s bound to be some free spirits:

Mrs. Robb’s bonnet, E. robbiae —root run and seed. An evergreen plant to one foot tall, able to withstand severe drought, shade, rooty soils and general neglect…see where this is headed?

Cypress spurge, E. cyparissias—root run and seed. Fine needle-like foliage to just eight inches tall, (tinged beautifully with maroon on the cultivar ‘Fen’s Ruby’) disguise vigorously spreading rhizomatous roots. I forgive its wanton ways for the feathery ruff it provides low, sprawling sedums along my gravel paths.

Griffith’s spurge, E. griffithii—root run. Beautiful russet foliage emerges nearly hot pink with spring bulbs, unfurling to about three inches and bursting into blossoms punched up with red to orange bracts depending on the cultivar. Slower in its inexorable spread, ‘Fireglow’ is too good of a companion to my orange lily-flowered tulips to give up; beautiful golden fall color as well.

9. Copper fennel, Foeniculum vulgare ‘Purpureum’—storage root and seed. Great fountains of feathery bronze foliage are a magnificent sight in the garden from their teddy-bear-like emergence in spring to their smoky bulk in late summer topped with golden umbel-shaped flowers. Young foliage is tasty, ripe seeds are delicious and the blossoms attract all sorts of butterflies and beneficial insects but oh, how it seeds and removal of the very substantial root will require the use of a mattock—if not a chain and a pickup truck.

10. Dragon lily, Dracunculus vulgaris —storage root/tuber. Some plants just look scary. Huge mottled snake-like stems charge out of the soil in mid-spring to three feet tall, giving rise to a huge, two-foot-long maroon “flower,” or spathe, that slowly unfurls over several days centered with a very suggestive black spadix. Beyond curious in its appearance this plant is also distinctive for the stench of decaying flesh it emits. I have been trying to dig mine up ever since it had the bad manners to bloom on the day of a garden tour, causing visitors to look politely, if not somewhat cautiously around in search of the dead body that must surely be hidden in the shrubbery.