Unwins Seeds

Growing biennial plants

02 July 2014 | Posted in Gardening by The Unwins Family

Growing biennial plants

Traditional biennial plants such as hollyhocks, foxgloves, sweet Williams, wallflowers and forget-me-nots are essential components of a country garden.

Spring flowering biennials such as honesty (Lunaria) wallflowers (Erisymum) and forget-me-nots (myosotis) look wonderful planted among spring flowering bulbs. And Sweet William (Dianthus barbatum) will flower well into midsummer to keep the garden colourful between spring and summer.

Foxgloves and Hollyhocks come into their own in high summer and they’ll add height, and considerable charm, to summer borders. Brilliant blue anchusa (alkanet) has recently come back into fashion; it took on a starring role in Cleve West’s 2014 Chelsea garden for M&G Investments.

All these biennial plants take 2 years to complete their growing cycle. The first year after sowing they put down roots and make rosettes of foliage, and in the second year they’ll send up flowers.

Bare root biennials and young plants

If you don’t want to wait 2 years for flowers, wallflowers and sweet Williams can both be bought as bare root plants in late summer and autumn. It’s the traditional way of buying them, and means you’ll be enjoying their lovely spring blooms much more quickly.

Sometimes biennials act more like short-lived perennial plants; they’ll often self seed and come back every year, so once you have these versatile and charming plants in the garden you’ll never need to be without them.

As well as buying biennials as bare rooted plants or getting them as young plants in spring you can also sow your own biennial plants now.  Many will germinate in as little as 7 days if soil is kept reliably moist.

How to sow

You can sow biennials such as wallflowers directly outside where you want them to flower or into a temporary nursery bed. But unless you have a large garden it is usually more convenient to sow seed into trays of good quality seed compost.

Sow thinly on the surface of the soil and cover the seed with a fine sprinkling of compost or vermiculite.

Water the trays and keep the compost damp but not wet.

Keep  at a temperature of 15-20C/59-68F until seeds germinate.

Once the seed has germinated, prick out the seedlings when they have two true leaves and grow them on at cooler temperature. Continue to water, and repot if necessary as the plants grow.

Plant out into their final positions in late summer or autumn when they are well- rooted young plants.  They’ll flower from spring next season.

Sowing TIPS Biennials germinate very quickly in warm summer temperatures so make sure you’ll be at home to deal with the seedlings. They’ll probably need watering everyday in warm weather so don’t disappear on holiday just as they need you most!

Growing TIPS Protect newly planted young wallflowers from flea beetles by covering them with fleece. The beetles don’t kill the plants but they do leave small holes in the foliage and stunt the plants growth.


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