Monthly musings: Biennials (April)

If you’ve had your work cut out getting to grips with the habits of hardy annuals (which stand some cold), half-hardy annuals (which aren’t the tiniest bit hardy) and tender perennials (which live for years but only if they’re kept warm in winter) then let me introduce you to another – and potentially even more confusing - class of flowers; biennials.

Biennials are flowers that grow one year and flower the next. After that, they either die off naturally or are pulled out by tidy gardeners since their job in the garden is over. But they can be very handy for situations where disposability is an asset. They are brilliant for such things as out-of-season containers, and for filling gaps in new borders while you wait for shrubs and perennials to grow.

Several popular garden flowers are biennials. Canterbury bells and sweet Williams are among the best, but have rather dropped out of mainstream gardening nowadays. And there are several we use regularly as winter and spring bedding plants – think of wallflowers, winter-flowering pansies and forget-me-nots. Some flowers, that are actually short-lived perennials, are often treated as biennials for convenience; think of aquilegia and foxgloves. And some biennials are classic cottage garden favourites. They include three stylish ‘thistles’: Miss Wilmott’s Ghost (Eryngium giganteum), the giant thistle (Onopordum arabicum) with seven-foot silver stems clad completely in matching prickles and topped by purple ‘knobs’, and the holy thistle (Silybum marianum) which is shorter with boldly marbled leaves and extra-spiky ‘knobs’ on top. There’s also the ethereal Verbena bonariensis with its invisibly thin wiry green stems topped by tufts of purple ‘cloud’, and down-to-earth honesty (Lunaria annua) whose variegated forms are particularly delightful.

To cap it all, several hardy annuals behave as biennials if there’s a mildish winter, and self-sow their own replacements. The trendy and enchanting honeywort (Cerinthe major ‘Purpurascens’) is one of the most welcome, with its grey-spotty foliage and nodding clusters of purple flowers, much loved by bees. But several poppies pull off the same stunt. Oh it can save you hours of gardening time as they do-it-themselves, creating the ultimate easy-care cottage garden border.

Sowing time varies slightly from species to species, but as a rule of thumb, expect to sow in late spring or early summer. Those with very small expensive seeds (such as winter-flowering pansies) are best sown in pots or seed-trays filled with multipurpose compost; prick-out the seedlings into small individual pots, then grow-on the resulting plants in a coldframe.

You can afford to take a more laid-back approach with biennials whose seeds are cheap, where you get lots per packet - wallflowers for instance. These are usually sown in rows in a seedbed, out in the open garden, and the seedlings thinned out (just like thinning carrots) to leave the plants a few inches apart, or else transplanted to a wider spacing. Then, in autumn, they are dug up and replanted in the places you want them to flower. When they fade, they are pulled out and thrown away - leaving fresh space with which to be creative. And that’s a real rarity in a small garden.