Annuals and biennials

Annuals and biennials are a cheap, easy-to-grow source of instant colour for borders, tubs, hanging baskets, window boxes and bedding schemes.

Annuals flower just once, but their ability to grow quickly from seed, their cheapness and their magnificent array of bright flowers should earn them a place in every garden. Many popular annuals, including petunias, lobelias, marigolds and asters, because of their warmer countries of origin are half hardy, so cannot be planted outside until after the last frost. They must be sown under glass in late winter or early spring and are relatively costly to buy as bedding strips.

Far cheaper are the hardy annuals such as larkspur, love-in-a-mist and candytuft, which can be sown straight from the packet outdoors, in seed beds or directly where they are to flower, in mid spring – or the previous autumn, to flower earlier. Their flowering season is often shorter than half-hardy annuals, but sowing them at fort-nightly intervals overcomes this problem.

Biennials such as sweet William, wallflowers and foxgloves are sown outdoors in early summer but produce only foliage during their first growing season. Flowering takes place the following spring or summer, after which they are usually discarded. (Some annuals and biennials can flower for a second or even third season but the size, number and quality of the blooms diminish.)

Given that they only flower from late spring or early summer to mid autumn, it’s better to incorporate annuals and biennials into mixed borders, or use them in containers to add intense splashes of bright colour near the house.

Most annuals and biennials flower best in sun, though some perform well in partial shade. Ordinary, well-drained soil is ideal; excessively rich soils result in lush foliage but few flowers.

Annuals and biennials generally follow the same stages of development. They are sown and thinned when large enough to handle, usually when there are two true leaves. The growing tips are often pinched out to promote bushiness, tall plants supported as necessary, and young plants kept watered, fed and weeded. Deadheading helps extend the flowering season.

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