Everything You Ever Wanted to Know About Biennial Plants
From hollyhocks to onions, what does it mean for something in your garden to be a biennial?
When you spend time in the garden, you quickly become familiar with the terms annual and perennial. You know that annuals live for just one season, while perennials (hopefully) live for many, many years. Less common are biennials, or plants that take exactly two growing seasons to complete their lifecycle. Read on to learn more.
How Does a Biennial Grow?
Biennials spend the first year of life focused on their roots, stems, and leaves. After a winter dormancy, the second growing season is marked by the plant growing exponentially, flowering, dying, and completing its lifecycle. Simply put: It's a two-year affair.
Common Biennial Flowers
A handful of biennials are common in the flower garden. They include Canterbury bells (Campanula medium), forget-me-not (Myosotis), hollyhock (Alcea rosea), foxglove (Digitalis), and sweet William (Dianthus barbatus). At your local garden center, you might find them tucked away with the other perennials rather than separated out in their own biennial section. All of these flowers self-sow freely and new plants often emerge right where a previous one lived, giving a perennial sense of a plant's presence in the garden, despite each one only living two seasons.
Can You Trick Them Into Blooming Their First Year?
While there are always exceptions to the rule, the short answer is no. These plants often need a period of winter cold to trigger their ability to flower.
Biennials in the Vegetable Bed
Many of the crops in our edible beds, including beets, Brussels sprouts, cabbage, carrots, celery, chard, collard, endive, kale, kohlrabi, leeks, onions, parsley, parsnip, rutabaga, salsify, and turnips are biennial. Though with many of these, we harvest them fully on their first year of growth, before they flower.
Given subpar conditions, many biennial vegetables will flower in just one season. But given that the bulk of biennials that we grow in the garden are veggies that we don't actually want to flower, you probably don't want to trick them into flowering early. It just means that you'll compromise your crop. We call it "bolting" when a leafy green goes to flower, rendering it inedible (or at least much less tasty). Same goes for onions, which will abandon their efforts in making big bulbs and flower instead if they aren't happy. Generally speaking, coaxing them along with the right sunlight and irrigation and preventing them from blooming too quickly is more desirable, especially for these veggies.
If your veggies do flower, they might no longer be edible, but you do have the chance to collect the seeds that form. If you live in a particularly cold climate, you might need to mulch your plants heavily to help them survive winter and reemerge in spring. But don't get too excited—many of these biennial crops cross-pollinate, meaning that the seeds won't come true to the parent plant unless you've grown them in isolation. So, unless you're planning to grow your Swiss chard and beets at least 800 feet apart, just enjoy their leafy greens and tender roots that first year, and replant again.