This is a comparatively small group but it does contain many of the loveliest and most useful garden plants. Biennials establish their roots and leaves in the first year, and then flower and set seed in the second. Some are technically perennials but make better garden plants when grown as biennials. You can grow them from seed or buy them as young plants. Treat them as you would a perennial, staking and watering as necessary. Below is a list of the plants most commonly grown as biennials.
Alcea (Hollyhock) – this is a perennial and if it settles happily in your garden you will get several years’ growth from it. They are tall plants with rounded, slightly hairy, leaves. Flowers grow up the stem throughout summer and come in a wide range of colors from white through pinks and yellows to a purply-maroon so deep it almost looks black.
Dianthus barbatus (Sweet William) – this is a perennial that does better as a biennial. In late spring and early summer the clumps of fine leaves are topped with flattish clusters of small sweet-smelling flowers in pinks and white.
Digitalis purpurea (Foxglove) – tall biennial (or perennial if it is happy) with spires of purple, white or apricot flowers in early summer. If you are lucky they will seed themselves and you will find your plants are regularly replenished.
Erysimum cheiri (Wallflower) – these are the perfect match for tulips in spring. Wallflowers grow into small bushy plants that look good all winter. They then flower at the same time as tulips in a wide range of reds and oranges and afterwards they hide the tulips’ fading leaves which tend to look unattractive.
Lunaria annua (Honesty) – this is an annual but produces better flowers and seed pods if it has a good start the previous year. It has attractively toothed leaves, and purple or white flowers up and down its stems in early summer. These turn into round, papery seed pods which will remain on the plant right up to winter.
Myosotis (Forget-me-not) – low carpeting plant with hairy leaves and dainty spring flowers in blue, white or pink. These look lovely under tulips. Strictly speaking they are short-lived perennials but once settled they self-seed prolifically and you will find your garden full of them. Some people will not grow them for this reason but they are so charming (and easy to pull up) that this seems a short-sighted approach.
Oenothera biennis (Evening primrose) – tall stems covered with fragrant bowl-shaped flowers throughout summer. The yellow flowers open fully in the evening and seem to light up the garden.
Onorpordum acanthium (Scotch thistle) – a spectacular plant with spiky grey-green leaves and thistle-like flower heads surrounded by spiny bracts. Beware as they can grow large.