All gardeners are familiar with annuals, those plants that flower for just one summer, then produce seed and die. The point of their short life is that their seeds fall to the ground sprout to bloom again the following year.
And we know perennials, those herbaceous plants that live for several years and generally flower for a shorter period during the year, but which compensate for this limitation by the ability to bloom again year after year, saving you a lot of replanting.
But biennials — those plants that make up the backbone of the classic English cottage garden and include so many “flowers our grandmothers used to grow” — are less well understood . . . and therefore less often used in modern gardens.
Short-Lived, But Long-Flowering
Biennials, as their name suggests, live for two years and then produce seed and die. But they don’t bloom both years. In the first year, they only produce foliage, usually a fairly low-growing rosette. Flowering occurs in the second year. And usually it is dramatic and long-lasting, often lasting two months or more.
Typically, biennials produce a tall spike of flowers the second summer. Flowering begins at the base of the spike and gradually moves up towards the tip. That explains why they bloom for such a long season.
Our Gardens Are Full of Biennials . . .
… But most are vegetables! Yes, Swiss chard, beets, carrots, celery, cabbage, Brussels sprouts, cauliflower, endives, turnips, onions, parsley, parsnips, leeks and rutabagas: all are biennials. We don’t usually think about them that way, because we harvest them during the first year. Therefore, we never see them bloom. However, if you leave these plants in the ground—and if the winter is not too cold! —, it’s in their second year that they’ll flower.
Biennials: Best Started From Seed
You won’t find a “biennial” section in any garden center that I know of. However, sometimes biennial plants are sold in the perennial section. Unfortunately, you then pay the price of a perennial for a plant that is in its second year of life and therefore destined to die at the end of the season! That’s why, when it comes to biennials, it’s best to buy seeds.
And they can all be grown from seed. Indeed, unless you apply extraordinary methods, you can only grow most biennials from seed. It’s not normally possible to propagate them from cuttings or division. Typically, you’d sow biennials between mid-June and mid-July, after your other garden plants. This gives you plants of just the right size to flower perfectly the second year.
You can sow biennials directly in a sunny border (some are fine in partial shade too), but it’s often more practical to create a small nursery where you can start biennials and other plants. I use part of my vegetable patch, freed for use after the earliest harvests, for that purpose. You can also sow them indoors in pots or trays, placing them in front of a sunny window.
Step by Step Sowing
There is rarely anything very special about sowing biennials. The same technique you habitually use to sow lettuce or zinnias is usually quite adequate. For beginning gardeners who have never sown lettuce or zinnias, though, here’s a quick summary.
Sow the seeds about 3 inches (5 cm) apart at the depth recommended on the seed pack. If this detail doesn’t appear, sow the seeds at a depth equal to about three times their diameter. Just dig a hole, drop in the seed and fill it with soil. Then water well. So easy!
Germination is generally fairly fast, within 3 to 14 days. Sometimes a bit more. The young plants will sprout and fill in, increasing in size. Often, they’ll be about the size of your fist in about 4 to 8 weeks. Then you can transplant them to their final location.
Just let them grow on their own, watering in case of drought. No winter protection is usually necessary.
Depending on the species, the plant can begin to flower as early as the following spring, but most will wait a bit longer, until summer.
Save Some Seeds!
As their bloom starts to die back, it’s important to allow at least a plant or two to go to seed. After all, these seeds are the key to future blooms. Indeed, when the seeds are left to ripen and fall to bare ground (you’ll have to remove any mulch), they’ll germinate on their own. So, in two years, you’ll have beautiful flowers again without lifting a finger! Almost all biennials are able to maintain themselves by self-sowing to at least a certain degree.
To Ensure Annual Blooming
If you sow your whole pack of biennial seeds the first year, it will result in a two-year cycle. You’ll have bloom year 2, nothing year 3, then you’ll have plants in flower in year 4, none in year 5, etc. Biennial flowering! So, remember to sow only half of the seed packet the first year, then the other half the second. As a result, you will create a flower border where there are always biennials in bloom every year!
10 Biennials to Discover
Here are 10 popular and easy-to-grow biennials.
1. Clary Sage (Salvia sclarea)
Dimensions: 30–48 in (75–120 cm) × 1 ft (30 cm)
Hardiness zones: 3b to 9
Very ornamental medicinal plant. Beautiful foliage with a rugged appearance. Very aromatic. White or purple flowers that last much of the summer. Sun. Well-drained, even sandy or rocky soil.
2. Forget-me-not* (Myosotis sylvatica)
Dimensions: 4 to 12 in (10–30 cm) × 6 in (15 cm)
Hardiness zones: 3 to 9
Many small sky blue, pink or white flowers. Self seeds abundantly . . . sometimes a little too much! Sun or partial shade, in any slightly moist soil.
3. Foxglove (Digitalis purpurea)
Dimensions: 3–6 ft (90–180 cm) × 2–3 ft (60–90 cm)
Hardiness zones: 3b to 8
Pink, purple, yellow or white trumpets, usually spotted, densely cover a sturdy stem. Sun or partial shade in any rich, well-drained soil. Attracts hummingbirds. Foliage highly poisonous: you can touch it, but don’t eat it!
4. Hollyhock (Alcea rosea)
Dimensions: 4–8 ft (1.2-2.4 m) × 2 ft (60 cm)
Hardiness zones: 2 to 9
Large rather round leaves. Edible single or double cup-shaped flowers in a wide range of colors, including black. Sun or partial shade. Any well-drained soil. Foliage prone to a disfiguring but otherwise harmless disease: rust. Simply grow the plant in the background to hide the weakening foliage from view. (Info: If You Can’t See the Problem, There is No Problem!)
5. Miss Willmott’s Ghost (Eryngium giganteum)
Dimensions: 3–6 ft (90–180 cm) × 1 ft (30 cm)
Hardiness zones: 5 to 9
This classic cottage garden biennial is a tall plant with heart-shaped gray-green basal leaves. In the second year, it produces a thick flower stalk bearing conical inflorescences surrounded by very prickly silver-grey bracts, like an Elizabethan ruff. The name “Miss Willmott’s Ghost” is partly due to its ghostly appearance in moonlight. But there is also a great story about it you can read here. Blooms from June to August.
6. Money Plant or Honesty (Lunaria annua)
Dimensions: 2–3 ft (60–90 cm) × 2 ft (60 cm)
Hardiness zones: 3 to 9
Rosette of toothed, heart-shaped leaves. Purple or white flowers followed by round, flat, silver-colored capsules (the “money” of its common name). Can be dried for decoration. Sun or partial shade. Any well-drained soil.
7. Moon Carrot (Seseli gummiferum)
Dimensions: 1 ½-5 ft (45–150 cm) × 1-1 ½ ft (30–45 cm)
Hardiness zones: 3b to 8
Quirky and pretty plant with strongly cut chalk blue leaves. Small balls of flowers, pink at first, but later becoming white, presented in sputniklike umbels. Moon carrot is so original it always attracts attention!
8. Scotch Thistle (Onopordum acanthium)
Dimensions: 6–9 ft (1.8-3 m) × 3 ft (90 cm)
Hardiness zones: 4 to 8
Spectacular thistle completely covered in white hairs, it forms a large rosette of spiny leaves the first year and a thick winged stem (also very spiny!) the second. Stem topped with a flower bud covered in spines. It opens into a dense mass of purple florets. Floral emblem of Scotland.
9. Silver Mullein (Verbascum bombyciferum)
Dimensions: 5–8 ft (1.5-2.4 m) × 2 ft (60 cm)
Hardiness Zones: 3b to 9
Rosette of foliage densely covered with soft white fuzz, giving it a silver-gray appearance and smooth texture. Thick stem so covered in down it looks like it’s made of white cotton! Lemon-yellow flowers. There are many other very beautiful biennial mulleins: silver mullein is just one example. Sun. Well-drained soil; even poor soil will do.
10. Teasel* (Dipsacus fullonum)
Dimensions: 4–6 ft (120–180 cm) × 1-1 ½ ft (30–45 cm)
Hardiness zones: 3 to 8
Originally grown to produce a tool for carding wool. Today, we mainly use teasel as an ornamental plant for its striking, spiny, pinecone-shaped inflorescences on strongly prickly stems. And also for use in dried flower arrangements. Lavender, pink or white florets. Also attractive are its opposite leaves which catch water and then serve as a drinking trough for birds.
Invasive or Not?
All biennials self-sow. And all of them could therefore be invasive if they are introduced into an area that is not their native one, but to which they can adapt to. It’s up to you, as a gardener, to be careful to prevent their excessive spread. For example, you can surround their planting space with mulch, which prevents seeds from sprouting. I have marked with an asterisk (*) the species more likely to be invasive than most.
Even More Great Biennials
And here are 10 other biennials to discover:
- Alpine poppy (Papaver alpinum). 6–8 in (15–20 cm) × 4 in (10 cm). Z: 3 to 6
- Angelica (Angelica archangelica). 3–8 ft (0.9-2.4 m) × 4 ft (1.2 m). Z: 3b to 9.
- Brown-Eyed Susan (Rudbeckia triloba). 4–5 ft (1.2-1.5 m) × 3 ft (90 cm). Z: 3 to 9.
- Canterbury Bells (Campanula medium). 2–4 ft (60–120 cm) × 2 ft (60 cm). Z: 3b to 9.
- Dame’s Rocket* (Hesperis matronalis). 2–3 ft (60–90 cm) × 2 ft (60 cm). Z: 3 to 9.
- Dyer’s Woad (Isatis tinctoria). 2–4ft (60–120 cm) × 1½ ft (45 cm). Z: 3 to 9.
- English Daisy (Bellis perennis). 3–6in (8–15 cm) × 4–6 in (10–15 cm). Z: 5 to 9.
- Korean Angelica (Angelica gigas). 3–5ft (90–150 cm) × 4 ft (1.2 m). Z: 5 to 9.
- ‘Ravenswing’ Cow Parsley* (Anthriscus sylvestris ‘Ravenswing’). 3 ft (90 cm) × 1½ ft (45 cm). Z: 2 to 10.
- Sweet William (Dianthus barbatus). ½-2 ft (15–60 cm) × 1 ft (30 cm). Z: 3b to 10.
Where to Find Biennials?
You’ll find seed packets of several biennials in better garden centers. Otherwise, try a mail order seed house, such as Veseys (www.veseys.com), Select Seeds (www.selectseeds.com), or Seedaholic (www.seedaholic.com). Personally, I often order mine from Chiltern Seeds (www.chilternseeds.co.uk) in England. I think they have a fine choice.
Enjoy discovering the beauty and advantages of biennials!
The ‘gift that keeps on giving’ is how we often refer to biennials here. Often they ‘give’ too much. My strategy is to deadhead the plants to reduce the number of self sowers. However, I also harvest the mature seedheads and scatter the seed about. The end result is lovely drifts of plants in the coming seasons.
Thank you for this article. We planted lovely foxgloves, with flowers, last year. This year we have a lot of shorter green plants, with no flowering stalks. Now I get it!