Biennials – Plants that Take Two Years to Bloom | Gardening

We know when to plant annuals and perennials and when to expect their blooms. However, biennials grow according to their own genetic schedule. Understand that and they are manageable members of your garden.

Biennials need two years to complete their growing cycle. The first year they produce roots, stems and leaves. The second year they produce flowers and seeds. Then they die. It’s not entirely that simple, but close. Some biennials like Sweet William (Dianthus family) are wily enough to live for three years and then suddenly die.

There is no early gratification to be found from planting ornamental biennials. A rosette-shaped clump of foliage the first year that blooms the following year makes for a long wait.

Dusty Miller is a plant that precludes the agony of expectation because it is grown for its foliage, not its flowers. However, when it flowers and dies it leaves some gardeners wondering if it is a short-lived or tender perennial.

Often when we buy potted biennials at the nursery they have already grown for a year and are ready to bloom in the current season. That includes some lovely garden plants like Clary Sage, Silver Sage, Canterbury bells, angelica, hollyhocks and foxglove. Then, surprisingly or not, the following year there are no blooms. What happened?

The original plant died. Seeds that may have sprouted were unknowingly weeded out or suppressed with a preemergent chemical. Even if seedlings grew they would not flower in their first year. An ongoing patch of biennials must be developed with time. It doesn’t happen in one season.

Biennials tend to produce significant amounts of seed. Evening Primrose (Oenotherea biennis), for example, which can grow more than 6 - 8 ft. tall, has long blooming fragrant yellow flowers. Considered a bee and butterfly plant, it is recommended for wild flower gardens and can be found in many wildflower seed mixes. This is not the invasive low growing evening primrose that spreads by underground runners. The biennial plant readily reseeds and is considered weedy in a well-tended garden.

Black-eyed Susans, like other biennials grow clumps of nondescript foliage the first year and flower the next. They are aggressive growers. During the season they bloom, you can divide the roots and plant the divisions for blooms next year.

Foxglove can do well in shade in our hot sunny climate. In the blooming year cut back the flower stalks after they bloom and the plant may send up more stalks to flower, but be sure to retain some seeds for future plants.

Similarly, with biennial sage flowering can be prolonged by removing flower stalks before they go seed.

Theoretically biennials die after blooming. You can take stem cuttings from some species during their blooming period, root them and plant them to produce flowers again next year. This can be done with Sweet William and wallflowers.

It doesn’t occur to many of us that a lot of the vegetables we eat are biennial. Their life cycle explains why we plant and harvest them when we do. We pick the leaves from leafy greens like Swiss chard, collards, endive and kale during their period of vegetative growth. We harvest the taproots of root vegetables like beets, carrots, parsnips, turnips and rutabagas later during vegetative development. The same is true for Brussels sprouts, broccoli, cauliflower, cabbage, kohlrabi, leeks, onions and garlic.

Among culinary herbs parsley is productive the first year and a half or so, it then flowers and goes to seed. Caraway, though grown less often locally, is not useful for more than a year until it goes to seed. You can direct seed either biennial in spring or fall for your desired harvest.

There are biennial weeds, too. There is no need to know which they are. Just be sure to get rid of all weeds before they flower and go to seed.

Start biennial seeds in the fall for blooms next year or in the spring for blooms the following year. Reseeding can be controlled by cutting off flower stalks before they go to seed and allowing a limited number of flower heads to produce seed.

This story was originally published August 6, 2016 at 5:00 AM with the headline "Biennials – Plants that Take Two Years to Bloom | Gardening."