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The Garden Decoder: What Are ‘Biennials’?


The Garden Decoder: What Are ‘Biennials’?

October 25, 2018

Let’s talk about biennials. A few springs ago, I planted a couple of foxglove plants. If you’ve been reading my Garden Decoder or Your First Garden posts, you know that plants, in general, don’t seem to like me very much. But those foxgloves, man, they adored me. They grew fast and strong, presenting me with multiple stalks, each heavy with healthy, large, bell-shaped flowers. Those two over-performers were a godsend, distracting the eye from the rest of my dreary garden with their showboating beauty.

The next year, though, they ghosted me. It’s as if I had dreamt the prior summer’s flush of blooms. Where did my foxgloves go? What did I do to offend them? I chalked up their abandonment to my black thumb. Most of the other plants in my garden hated me. Of course, they would, too.

But I needed closure, so I started to search for some answers. Turns out, it wasn’t me, it was them. Read on for everything you need to know about biennials:

N.B.: Featured photograph courtesy of Farlam & Chandler, from Before & After: A Seaside English Garden by Farlam & Chandler.

What are “biennials”?

Above: Tall stems of pink foxgloves, which are biennials, at the Tuileries in Paris. Photograph by Alice Gao, from Garden Visit: The Tuileries at Sunset, with Alice Gao.

First, let’s define the term’s better-known counterparts: annuals and perennials. Annuals (like zinnias, petunias, snapdragons, and sunflowers) have a life cycle of just one growing season; after they flower and produce mature seeds, they die. Perennial flowers (think: lavender, asters, day lilies, and peonies), on the other hand, continue to grow and bloom for three years or more.

I have never understood the appeal of annuals (what’s the point of growing plants that last just a few months?), so I’m sure that I didn’t find the foxgloves in the annuals section of the nursery. They must have been placed in the perennials section, yet they’re not quite perennials, either. Enter the third category of plants: biennials.

Biennials—including foxgloves, evening primrose, and Iceland poppies—have a life cycle that takes two years. In the first year, they grow from seeds into small plants; in the second, they bloom.

Keep in mind: Plants are classified as annuals, biennials, or perennials based on their behavior in their native region. For instance, tulips are technically classified as perennials, and in parts of the world where they’re native (e.g., eastern Turkey or the foothills of the Himalayas), they, indeed, come back year after year. However, here in the US, they behave like and are treated as annuals.

Do biennials self-seed?

Self-seeded honesty (Lunaria) in the crook of a tree. Photograph by Jim Powell for Gardenista, from Gardening \10\1: Honesty.
Above: Self-seeded honesty (Lunaria) in the crook of a tree. Photograph by Jim Powell for Gardenista, from Gardening 101: Honesty.

Yes, many do. In fact, most flowers that self-seed are either annuals or biennials. (This explains why a small foxglove plant showed up this year just a couple feet away from where I had originally planted my foxgloves.) So even though a biennial mother plant may die after two years, its offspring may sprout up spontaneously elsewhere on your property. Other reliable biennial self-sowers include forget-me-nots, sweet Williams, honesty flowers, and black-eyed Susans.

Are the biennials sold in stores in their first or second year?

Most biennials you find in nurseries are already flowering and in their second year—which means you’re essentially taking home an annual when you buy a biennial. It will grow and bloom and likely won’t come back the next year. If you want to experience its full two-year cycle, sow the seeds yourself in the summer and transplant the seedlings into their flowering spot in your garden in autumn; they should flower the next spring.

For more on sowing seeds, see DIY Seed Starting: Newspaper Pots. For more on foxgloves, see Foxgloves: Rethinking a Fickle Flower and Gardening 101: Foxglove.

For more beginner gardening advice, be sure to check out:

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