Half-hardy annuals are very sensitive to the cold, so need to be sown indoors in spring and planted outside in early summer when no more frosts are forecast. They'll keep going until the first autumn frosts.
Despite their exotic looks, half-hardy annuals are surprisingly easy to grow. Growing them from seed will give you a much wider choice of varieties than you’ll have if you buy ready-grown plants, and some species will flower in as little as 12 weeks.
Find out how to sow half-hardy annual seeds.
Prick out seedlings into pots or multi-cell trays and grow them on into sturdy plants, ready to drop into border gaps. Dot single plants as accents through your borders, or plant generous drifts between perennials, providing a contrast of foliage and colour.
Watch Monty Don's video guide to boosting borders with half-hardy annuals.
Here are 10 beautiful half-hardy annuals to grow.
With soft, ferny foliage and delicate blooms, cosmos mingles well in any border and makes a great cut flower. Regular cutting keeps the blooms coming. Height 40-90cm. Flowers in 14 weeks. Find out how to sow cosmos seeds.
There are many colours of nicotiana to choose from, including white, lime green and purple. Wonderful scented foliage and flowers. Height: 90-150cm. Flowers in 16 weeks. Find out how to grow nicotiana from seed.
Often relegated to greenhouses or border edges, large-flowered african varieties of tagetes also make a striking centre piece. Height: 60-90cm. Flowers in 16 weeks. ('Tall Scotch Prize' is pictured here.)
Spider flowers, Cleome, have impossibly intricate blooms in white or pink. Combine with large dahlias in pastel shades. Height: 90-120cm. Flowers in 14 weeks.
Zinnias are available in many vibrant colours, so there’s one of these zingy daisies to suit every colour scheme. They also make excellent cut flowers. Height: 30-90cm. Flowers in 16 weeks.
Climbers, like this cup-and-saucer vine, Cobaea scandens, quickly cover unsightly walls. They can also be trained to make a feature up an obelisk. Height: 6m. Flowers in 16 weeks.
Amaranthus bear fuzzy flowers in bold spikes or weeping tails. Choose from plants with red or green flowers and foliage. Height: 45-120cm. Flowers in 12 weeks.
Very quick and easy to grow, nasturtiums produce long, trailing stems covered in neat, round leaves and bright flowers in fiery shades. They are a good companion plant and the flowers are edible, too. Spread: 35-100cm. Flowers in 10-12 weeks.
Verbena x hybrida
Mildew-resistant Verbena x hybrida 'St George' has deep green foliage and a spreading habit. Stunning red and white flowers. Height: 15-25cm (6-10in). Flowers in 14 weeks.