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foxglove digitalis types is it biennial or perennial

Foxglove - Will the Real Biennial Please Stand Up?

by Mary Jasch

If any herbaceous plant is non-stereotypical, it must be the foxglove. It defies classification of which there seems to be three. It reproduces abundantly in just the right places, then blooms with stellar showmanship and exits with ethereal aplomb. Call them biennial, short-lived perennial, true perennial or even sterile, these showstoppers are a must for East Coast gardens.

At Laurelwood Arboretum in Wayne, New Jersey, a great swath of white foxglove covers a hillside in spring. Descendants of a long line of Digitalis purpurea in the 30-acre garden and nursery of Dorothy and John Nippenburg, these ethereal perennials are treasured to this day. The property, bequeathed to Wayne Township in the 1990s, is now a public garden and is cared for by the Friends of Laurelwood Arboretum.

The digitalis there are strictly white, per Knippenberg wishes, so errant pinks are removed. There, mother plants often live for more than two years and compost is the only fertilizer. “It depends on how you take care of them. If they want to live another year they will. I have noticed that foxgloves will last maybe three years,” says Joan Scott-Miller, Laurelwood’s horticulture manager for 17 years and Dorothy Nippenburg’s protégé. “Seeds germinate and I leave them and let them live with each other. I just let them be.”

Ken Selody, owner of Atlock Flower Farm, Somerset, New Jersey, grows ‘Foxy’ and a mix of D. purpurea. He sells rosettes that he starts from seed in January or February. “Occasionally I’ll get a garden full of rosettes. You can’t do too much disturbance of the soil. They grow where there’s no mulch or leaf litter. They will germinate and grow where they want to. They tend to put themselves in really good spots. If you go in and thin them be careful not to do it in an artificial way – no straight rows. They seem to know how to come up where they need to come up.”

At Bill Kolvek Perennials in Spring Valley, New York, owner Bill Kolvek grows the most famous foxglove “biennial” D. purpurea “Excelsior” mix and named cultivars like white Alba, Spice Island and the shorter “Foxy” hybrids. He also grows the short-lived perennial D. mertensia (D. ambugua) and yellow D. grandiflora a “true perennial” and the hardiest of them all.

Digitalis grandiflora is super weedy with lots of seedlings, says Barb Pierson, nursery manager, White Flower Farm (WFF) in Morris, Connecticut. Mother plants last a couple years. They will if they’re happy but it won’t last. They’re so tough. If they’re happy where they are they will thrive and reproduce. Same thing for hollyhocks. My mother plant has come back for two years.”

White Flower Farm grows the salmon-gold ‘Polka Dot Pippa’ a sterile hybrid of D. purpurea and another strain. The foliage is not similar to purpurea so the other parent is completely different. The plant is bred by Walter’s Garden in Michigan, part of the Proven Winners Group. WWF buys and grows them on. They grow all ‘Excelsior’ hybrids from seed.

“When Polka Dot Pippa’ grows in the garden it does exactly what they tell you it’ll do. It is sterile and doesn’t set its own seed,” says Pierson. “It is propagated vegetatively by tissue culture. It does develop a seed head and it’s possible it sets non-viable seed. It is truly perennial and blooms for at least three years in the garden,” says Pierson.

“I’ve seen it with all the digitalis I’ve ever had, the way the mother plant dies after a year, but that’s not my experience in the garden. That’s why it’s so hard to talk about digitalis to new gardeners. The life cycle is confusing. The mother might die in a year. People should always leave any plants they see and only take out the dead ones.

“Be sparing with your thinning. If you’ve got a big mother plant, leave it. Those plants that do overwinter are huge. They’re the really good ones. In fall you may see seedlings. Don’t thin them. Wait till spring because winter’s going to take out some of them. Winter does a lot to seedlings,” she advises.

Laurelwood’s Scott-Miller recommends that gardeners buy and grow plants for three years. “If you want foxglove, you have to keep planting them for a while. You have to think big when growing foxglove. Plant them in swaths and not in full sun – they’ll go in full sun if they want to. Start with twelve and the next year put another twelve in. Eventually you get seedlings. Foxglove will grow where it wants to. The seeds will go everywhere but it chooses its own place. Humus in soil and good drainage are essential.”

Most importantly, she says, “Lay in the foxgloves for three or four years if you want to have an effect.”

Species & Varieties
D. purpurea is referred to as biennial, although the consensus is the mother plant often blooms for two or more years.
D. purpurea ‘Foxy’ grows two-three feet tall and often blooms the first year.
D. purpurea ‘Excelsior’ hybrids are a real impact plant. Its flowers stand face out on the stem.
D. mertonensis, strawberry foxglove, grows three-four feet and is shades of pink.
D. grandiflora, (D. ambigua), has large yellow flowers and grows two-three feet.
D. ferruginea, rusty foxglove, has yellow to brownish flowers with interior rust-colored veins and long lower lip on a thin, three-five foot stem.
D. ‘Polka Dot Pippa’, sterile cross with flowers all around the stem.

General Care
Thought for the day: Digitalis is more like a tender perennial and not even that – an ethereal perennial, mysterious perennial. “Ditto for hollyhocks in my experience” says Pierson. They all self-sow except for Polka Dot Pippa. Plant in sun to partial shade. They like fairly constant moisture with good drainage and will rot in winter in heavy soils.

Some say that deadheading may encourage re-blooming but be sure to leave some flower spikes. Says Pierson: “Leave the seed on the plant and make sure there’s open soil for the seed to be distributed. If there’s nowhere for seed to drop and germinate, it won’t. In spring, make sure you don’t weed out the seedlings. The mother plant may come back too.”

Transplanting Rosettes
If one day in late summer you discover a patch of tiny seedlings, that is the time to transplant and separate them, if you wish, before they grow and their roots become entwined. Be warned: the tiny rosettes grow fast. If you don’t have the chance to move them immediately when they are small and at a distance from each other, let them be until spring. Winter will determine which survive.
Scott-Miller: “Let them overwinter and see what comes up.”

If you want foxglove where it isn’t growing, perhaps it’s best to buy plants and let them go to seed.

Bill Kolvek doesn’t fertilize his foxgloves or perennials in general. Instead, he amends the soil with compost, leaf mold, and organic fertilizer like Plant-tone. If the soil needs extra nutrients, they might add bonemeal, greensand and kelp meal. As with over-fertilized grasses that grow lanky, Kolvek finds that perennials like it on the lean side too. “Give it a good, basic start and let it grow. That way you’ll get tough growth. That’s exactly what’s happening in the woods. No one’s taking care of the woods.”

Laurelwood Arboretum
Atlock Flower Farm
Bill Kolvek Perennials
White Flower Farm
** Top photo by Joan Scott-Miller

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published December 12, 2013

Photos to enlarge

Self-seeding Digitalis purpurea on a hillside at Laurelwood Arboretum in Wayne, NJ, with an errant pink among the white. Betsy Hays Gatti photo

D. purpurea 'Excelsior' hybrids in a dsplay garden. Photo courtesy White Flower Farm

The sterile 'Polka Dot Pippa'. Photo courtesy White Flower Farm

D. ferruginea, Mary Jasch photo

Excelsior hybrids at White Flower Farm, Mary Jasch photo

Digitalis punctuates a walk at the Cross Estate Gardens at Morristown National Historical Park, NJ. Mary Jasch photo

Foxglove (D. purpureaself-sown rosettes cover a slope in a private garden in Warwick, NY. Mary Jasch photo

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