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Article

Biennials That Are Worth Your Time

A truly varied and interesting garden is impossible without these plants, which grow foliage the first year and flowers the second

Fine Gardening - Issue 150

You may already think that you know what a biennial is. Maybe you’ve said, “Why bother?” to yourself all these years. You’re not interested in something that just grows a lot of leaves the first year, flowers something marvelous the second year, then croaks. Well, I’m here to tell you why you should grow biennials, and that reason is simple: because other gardeners aren’t. Anyone can pop a perennial in the ground and have it forever. But you, my friend, have cultivation patience!

But seriously, even though most biennials are simply gorgeous, you don’t find them in many gardens; that’s because people just don’t know how to manage them. Or if you have seen them, you might not have known that they were biennials: Because some biennials are uninhibited reseeders, they seem to come back year after year. I couldn’t grow a truly interesting and varied garden without the help of some of my favorite trusty and funky biennials. If you have the patience, won’t you consider growing some?

Perennial vs. annual vs. biennial:

What’s the difference?

The line between peren­nials, annuals, and biennials is a zigzaggy, dotted one. Perennials live longer than three years, annuals for just one, and biennials wrap it up in a two-year life cycle. Some plants are perennial in one zone and annual in another. And to make it more complex, some biennials can’t tell time and live longer than two years. The good news is that no matter what you buy, you know your new plant is going to be one of the three.

 

1. ‘Banana Custard’ mullein relishes the heat

Name: Verbascum ‘Banana Custard’

I thought I had killed every mullein I’d ever grown, including this one, but it turns out that they’re just biennials and I’m not the serial mullein killer I thought I was. I find the color on most mulleins to be muddy or weird, but I like the clear color, stocky stems, and long bloom time of ‘Banana Custard’. If you plant the seeds in full hot sun in spring, you’ll get rosettes the first year and flowers on tall stems all summer long the following year. Let them self-seed, if you dare. When I bought this plant—in full bloom (duh!)—I planted it in front of a purple clematis (Clematis cv., Zones 4–11) on a trellis with some ‘Fireglow’ euphorbia (Euphorbia griffithii ‘Fireglow’, Zones 4–9) and bells of Ireland (Moluccella laevis, annual) nearby. Wow! Don’t ever overwater mulleins—they will hate you for it.

USDA hardiness zones: 4 to 9

Size: 3 to 6 feet tall and 18 inches wide

Conditions: Full sun; well-drained soil

 

2. ‘Victoria Blue’ forget-me-not is like spring confetti

Name: Myosotis sylvatica* ‘Victoria Blue’

Photo: courtesy of David Monniaux/commons.wikimedia.org

This little wildflower combines so well with spring bulbs that there should be a law stating that they have to be grown together. Forget-me-nots are old-fashioned, rampant reseeders that may have you fooled into thinking that they are perennial. ‘Victoria Blue’ forget-me-not isn’t new to most and is a nuisance to some, but it’s a charmer to me and I don’t get tired of it. But if I did, I could rip its tired foliage out by the handful after it had gone to seed and not have to worry about it again until spring. It looks hot with ‘Aureola’ Japanese forest grass (Hakonechloa macra ‘Aureola’, Zones 5–9) and cool with blue dune grass (Leymus arenarius, Zones 4–10).

Zones: 5 to 9

Size: 6 inches tall and wide

Conditions: Full sun to partial shade; moist, well-drained soil

 

3. Alpine poppy is a delicate pastel beauty

Name: Papaver alpinum and cvs.

If you have an empty square-foot spot in your garden and like flowers that are the colors of late 1970s’ prom dresses, this is the plant for you. Like flimsy, dainty lamp shades, the flowers of alpine poppy have movement and joy, so much so that I feel compelled to plant it next to a gargoyle or something. If you situate this plant where it isn’t too, too hot, you’ll get sporadic flowers throughout the second summer. Sow these seeds in late fall, in winter, or in early spring; it doesn’t really matter where or when because the plant will come up where and when it pleases, flowering the second year. If allowed to reseed after it flowers, it may not come up exactly where you want it, but it will be where it works for this plant. Team alpine poppy with sultry ‘Black Scallop’ ajuga (Ajuga reptans* ‘Black Scallop’, Zones 3–9) to bring the cute factor down to a manageable level.

Zones: 5 to 8

Size: 6 to 8 inches tall and 4 inches wide

Conditions: Full sun; sharply drained soil

 

4. Korean angelica is tall, dark, and handsome

Photo: Michelle Gervais

Name: Angelica gigas

A lovable giant, much like Hagrid but a lot more elegant, Korean angelica rises out of the garden like a skyscraper. It’s truly different. You only need one, really, but if you plant more than that, we should be friends. If you deadhead it reliably, Korean angelica may be a perennial for you. I like to team it with ‘Hamer Pandora’ blue throatwort (Trachelium caeruleum ‘Hamer Pandora’, annual) or ‘Snowbank’ boltonia (Boltonia asteroides ‘Snowbank’, Zones 4–8).

Zones: 4 to 9

Size: 3 to 6 feet tall and 3 feet wide

Conditions: Full sun to partial shade; moist, fertile soil

 

5. ‘Milk Chocolate’ foxglove offers an unusual color combo

Name: Digitalis parviflora ‘Milk Chocolate’

Photo: Bill Johnson

How will the faeries have chapeaus if you don’t grow old-fashioned and romantic foxglove? Its towering shape and ladylike colors bring something unique to the table. I love this Yoo-hoo–colored foxglove because the color makes people look not just twice but seven or eight times. I like to keep the color scheme simple around ‘Milk Chocolate’ because its colors run a wide spectrum of brown, rust, yellow, peach, and red. It’s a natural in the same border as hollyhock (Alcea rosea* cvs., Zones 3–9), but it’s also a deer-resistant buddy for ‘Chocolate Ruffles’ heuchera (Heuchera ‘Chocolate Ruffles’, Zones 4–9).

Zones: 4 to 9

Size: 2 feet tall and 1 foot wide

Conditions: Full sun to partial shade; average soil

 

6. Money plant offers blooms and fancy seedpods

Name: Lunaria annua* and cvs.

Photo: Bill Johnson

It may be on the rampage as an aggressive plant in some parts, but I can’t get enough of money plant here in Chicago. But its purple phloxy early-summer flowers aren’t what get me excited—it’s the seedpods. When dried, they can be used in arrangements or made into amazing wreaths. For pure reseeding joy, grow money plant with other plants that have a lust for life, like tall verbena (Verbena bonariensis*, Zones 7–11) and red corn poppy (Papaver rhoeas, annual).

Zones: 3 to 9

Size: Up to 3 feet tall and 1 foot wide

Conditions: Full sun to partial shade; moist, fertile, well-drained soil

 

7. ‘Heart Attack’ sweet William will stop you in your tracks

Name: Dianthus barbatus ‘Heart Attack’

A 1-foot-tall mass of chocolate-covered cherries that blooms most of the summer? Yes, please. I find all other sweet Williams on the obnoxiously sweet side, perhaps even a bit garish (if you’ve ever seen my wardrobe you’re laughing heartily right now). But ‘Heart Attack’ sweet William is a showstopper and blends terrifically with the rest of the garden, with characteristics typical of the genus: evergreen in well-drained soil and full sun and not favored by deer. Pair ‘Heart Attack’ with lacy ‘Powis Castle’ artemisia (Artemisia ‘Powis Castle’, Zones 6–9) or ‘Berggarten’ sage (Salvia officinalis ‘Berggarten’, Zones 5–8).

Zones: 3 to 9

Size: 1 foot tall and wide

Conditions: Full sun; well-drained soil

 

8. Stock is fantastically fragrant

Photo: Stephanie Fagan

Name: Matthiola incana cvs.

If ever you need to take a car trip with a plant in the passenger seat, I highly recommend it be stock. The scent is strong but not too sweet; it’s a little spicy, and it seems to change with each inhalation. Intoxicating. You most likely think of stock as a spring annual, but it is a biennial whose cultivars have been bred to flower their first year. It may require a little winter protection in cool zones; give it about a 3-inch-deep layer of leaf litter and you’re good to grow.

Zones: 5 to 8

Size: Up to 32 inches tall and 16 inches wide

Conditions: Full sun; moist, fertile, well-drained soil

 

9. ‘Ravenswing’ cow parsley is a study in contrast

Name: Anthriscus sylvestris* ‘Ravenswing’

Photo: Nancy J. Ondra

‘Ravenswing’ cow parsley looks like a black fern the first year, then the second year, it sends up tall spikes topped by umbels of white flowers that pop against the foliage. This is a biennial whose flowers I could skip because I’m so cuckoo over its foliage. I imagine I could get a similar look from my Black Lace elderberry (Sambucus nigra ‘Eva’, Zones 4–7), but I like them together in the same bed, balancing each other out (just not right next to each other). If ‘Ravenswing’ reseeds, make sure you pull out any seedlings that have reverted to boring green. I insist you plant this with a gaggle of variegated irises (Iris pallida ‘Variegata’, Zones 4–9) and lots of artichokes (Cynara scolymus, Zones 8–9) that you allow to flower.

Zones: 7 to 10

Size: Up to 3 feet tall and 2 feet wide

Conditions: Full sun to partial shade; well-drained soil

 

10. Black hollyhock gives a garden an edge

Name: Alcea rosea* ‘Nigra’

Photo: courtesy of perennialresource.com

Hollyhocks are an old-fashioned garden staple. But I can’t tell you how many people think that they’ve failed at growing them by not realizing that they are biennials. I particularly love black hollyhock—and not just because Thomas Jefferson grew it at Monticello. The plant’s size and bulk are impressive, and its dramatic, maroonish black cups reach up from the back of the border, eventually bending into a deep curtsy as the season wears on. Hollyhocks come with leaf miners, so plant your hollyhocks so that the leaves are blocked by other plants but still get some sun. I like to plant ‘Chocolate’ eupatorium (Eupatorium rugosum ‘Chocolate’, Zones 4–8) in front and ‘Black Jack’ gladiolus (Gladiolus ‘Black Jack’, Zones 8–10) not too far away.

Zones: 3 to 9

Size: Up to 5 feet tall and 2 feet wide

Conditions: Full sun; fertile, well-drained soil


How to turn your biennials into pseudoperennials

I like to grow biennials in a loosey-goosey, free-form garden, where chaos is king and the colors of the rest of the crowd cover up that first year’s foliage; then the second year’s blooms are gravy. But if you want to grow them within your regular perennial beds, you’ll need a strategy. Here’s a system for keeping your biennials happy and present from year to year.

Year 1

Spring

Sow your seeds, or buy first-year plants.

Summer

Treat your first-year plants like you would any perennial. Avoid hiding the foliage, which might block the sun the plants need to thrive.

Fall

Cut back the plants as you would any peren­nial, if that’s your style. Tender plants might require mulching.

Year 2

Left to right: Spring, Summer, Fall

Spring

As your biennials begin their second year, sow a second round of seeds or buy a second round of first-year plants to add to the garden.

Summer

Enjoy your second-year plants’ flowers, and nurture the foliage of the new first-year plants.

Fall

Let your second-year plants go to seed and sow themselves. Treat your first-year plants like any other perennial.

Year 3

Spring

You now have the second-year plants coming up and flowering and the seeds from your first-year plants germinating.

Tip – Want to cheat?

If it’s the foliage you’re after and not the second-year flowers, prune out flowering stems religiously in the second year to trick your biennial into coming back for a third year—maybe even a fourth.


Amanda Thomsen is a landscaper in Chicago, Illinois, and the author of the book Kiss My Aster. She blogs for Fine Gardening at FineGardening.com/series/Kiss-My-Aster.

Photos, except where noted: millettephotomedia.com, Illustrations: Martha Garstang Hill

The following mail-order seed and plant sellers offer the widest selection of the biennials featured:

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