If you didn’t thoroughly clean out your vegetable garden last fall (which, incidentally, you certainly don’t need to do, as any laidback gardener will tell you), you may be surprised to see a few vegetables left in the ground start to sprout and come into bloom.
This happens largely because many of those vegetables we grow as annuals—cabbages, beets, Swiss chard, carrots, onions, etc.—are not really true annuals, but rather biennials, biennials being plants that bloom and produce seed the second year. Since we harvest them for the table the first year, normally we never see them go through their full life cycle. But if, accidentally or intentionally, you leave them in the ground over the winter, you just might discover a completely different aspect of these plants when they grow back the second year.
Annual by Harvest, Biennial in Habit
Biennial vegetables grow the first year, storing solar energy in their leaves, a thick stem or a fattened root. The second year, they spend what they stored up. All that energy is now invested in producing flowers and seeds. And usually the plant charges its shape quite dramatically.
For example, a head cabbage barely 18 inches (45 cm) high the first summer soon reaches for the sky the next spring, forming a tall, branching stem much like a small tree and up to 7 feet (2 m) in height bearing hundreds pale yellow or white flowers.
Beets are almost as tall as cabbages when they bloom, again forming a branching inflorescence, but this time with red stems (if the beet was red) and green flowers. Most people would never guess the curious plant sprouting in their vegetable bed is a beet!
And Then Come Seeds
Seed growers rely on this second-year bloom for the seed they harvest and bag … and you can let a few vegetables produce seed as well, at least in climates where winters are not too harsh. That’s because many common vegetables are of Mediterranean origin and won’t necessarily survive where the soil freezes solid. You can often help them survive the winter by mulching them thickly in the fall, as mulch keeps the soil considerably warmer. Or, dig them up in the fall and overwinter them in a root cellar, then replant them the following spring so they can bloom.
When Biennials Flower the First Year
When a biennial flowers the first year (and that can happen), it’s called bolting and it’s usually the result of some sort of shock to the plant’s system: extreme cold or heat, deep drought, root damage, etc. Or a very long growing season. Bolting is usually considered undesirable because, as soon as vegetables start to bloom, most become bitter, woody or otherwise inedible, which rather defeats the point, as we normally grow these plants so we can eat them.
Our ancestors, however, did manage to develop annual varieties of a few biennial vegetables, plants designed to bloom the first year. Broccoli and cauliflower are the two best-known. They’re derived from biennial cabbages selected for their ability to flower the first year and to produce short, very compact, edible flower heads. Even so, you have to harvest both broccoli and cauliflower at just the right stage. If you delay, the stems lengthen, the flowers start to open and the taste goes out the window.
The artichoke too was originally a biennial plant, but strains were developed that flower the first year. With artichokes, we eat the bracts that cover the flower bud … and again, you have a very tight harvesting window. If you wait too long, they’re no longer edible.
The Most Popular Biennial Vegetables
Here is a list of “annual vegetables” that are actually biennials or, in some cases, even short-lived perennials.
- Beet (beetroot)
- Black salsify
- Brussels sprouts
- Chinese cabbage
- Swiss chard
- Winter radish (daikon)
And remember, whenever a biennial vegetable blooms, be it by accident or on purpose, it’s always a good source of free seed for next year’s garden!