Biennials to sow in July

foxgloves on a terrace
Tall foxgloves brighten up this stylish terrace
Image source: Del Boy

If you’re itching to sow seeds in June and July, try beautiful biennials for colour next spring and summer. These wonderful plants complete their life cycle in two years. In the first they form roots and leaves, and in the second year they flower. It might seem like a long wait, but it’s worth every minute of it.

Sowing biennials

sowing into seed trays
Put empty seed trays to good use this June and July.
Image source: Rob Kemp

Sow biennials when your seed trays lie empty following the spring sowing frenzy. They’ll happily bide their time, out of sight, until the following year when they strut their stuff before most annuals have hit their stride.

I use modules or trays, but you can sow biennials directly into a nursery bed. I water the compost before sowing. After this initial soak,  water  the compost from below, by standing the trays in shallow water.

Foxgloves and Canterbury bells need light to germinate, while other biennials require a sprinkling of soil, compost, vermiculite or grit. Once sown, pop them in a corner of the garden, and let them get on with the business of germinating.

Keep them moist, and you should see seedlings emerging within two weeks (or a little longer for Canterbury bells). If they’re sown in open ground, thin them out to about 5cm (2”) apart once they have their first set of true leaves. Seeds sown in modules or trays can be pricked out and grown on in 9cm (3”) pots.

Although biennials should be planted out in autumn, I always keep a few back in pots until spring and use them to fill gaps in the borders. These potted plants always thrive – even after our most challenging winters. Hardy biennials really are the most accommodating plants.

Must-have biennials

tulips in forget me nots
Tulips look magnificent against a swathe of biennial forget-me-nots.
Image courtesy of Michael King of Perennial Meadows

Wallflowers (Erysimum cheiri) mingling with tulips is a popular spring combination, and getting the look is easy because biennials are ready to be planted out in autumn, neatly coinciding with spring bulb planting.

To avoid slicing through bulbs, always plant biennials first, then arrange the bulbs around them. Wallflowers are actually short-lived perennials, but we treat them as biennials. They’re a valuable addition to spring containers and borders, and they make excellent cut flowers.

Forget-me-nots (Myosotis sylvatica) provide a gentle froth of flowers and foliage between tulips or daffodils, and soften the edges of paths or provide colour at the front of borders. They also work beautifully with strawberry flowers in a patch or in pots.

Foxgloves (Digitalis purpurea) shine from shady corners in the garden. I plant white foxgloves in large swathes in the dappled shade of trees, where their foliage suppresses weeds and their majestic flower spikes lift what might otherwise be a dull area in the early summer garden.

At RHS shows we often see foxgloves adding height to a shady planting scheme or picking out the colour of decorative bark. If you grow shrubs or trees with beautiful bark, consider sowing foxgloves to accentuate its colour.

Scented sweet Williams (Dianthus barbatus) make great cut flowers. I use them to add a splash of colour to borders in early summer, and to fill the gaps left after tulips have finished flowering. Sweet Williams thrive in alkaline soil, so if you garden on acid soil, try growing them in pots in a sunny spot.

Canterbury bells (Campanula medium) are a beautiful addition to borders. Deadhead these cottage garden favourites regularly to prolong flowering. Despite being biennials, they produce more flowers if they’re cut back before they have a chance to set seed.

Pride of the Pollinators

butterfly on sweet william
Butterflies and other pollinators love scented sweet Williams.
Image source: Yuttana Joe

Sweet Williams, Canterbury bells, wallflowers, forget-me-nots and foxgloves are all attractive to pollinators. Fortunately there are usually plenty of seeds in a packet, so we can help pollinators by growing lots of flowers for very little outlay. Biennials will seed themselves around, making them even better value for money, although to get flowers every spring and summer, you’ll need to be mindful of their biennial nature and sow them in two consecutive years.

So scratch that itch to sow seeds now. When next year comes, you’ll be glad you did – and so will our precious pollinators!

What are the best biennial seeds to sow in July?

canterbury bells
Campanula medium (Canterbury bell) comes in a variety of colours
Image source: Rafaella Galvani

Plan ahead for next spring and summer by sowing the following biennial seeds:

  • Campanula medium (Canterbury bell)
  • Dianthus barbatus (sweet William)
  • Digitalis purpurea (foxglove)
  • Erysimum cheiri (wallflower)
  • Hesperis matronalis (sweet rocket)
  • Papaver nudicaule (Iceland poppy)
  • Lunaria annua (honesty)
  • Myosotis sylvatica (forget-me-not)
Sarah Shoesmith

Author: Sarah Shoesmith

Sarah Shoesmith was awarded the Centenary Prize by the Royal Horticultural Society in 2003, and gained a Distinction in the Diploma in Garden Design from The English Gardening School. She is passionate about gardening for wildlife and growing food, and writes about gardening for magazines and other sites.

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