Colours of Summer: Growing Annuals and Biennials

Colours of Summer: Growing Annuals and Biennials

Annuals are plants that complete their life cycle within one year and then die, leaving seed behind to germinate the following spring and continue the cycle. That is the strict definition but gardeners stretch it to include some plants that, though they do not automatically die after they have flowered and set seed, are nevertheless best renewed annually from seed.

Gardeners also, for convenience of handling, divide annuals into three groups: hardy, half-hardy and tender. The hardy kinds can be sown outdoors in spring where they are to flower in summer and little more will be needed except to thin out the seedlings, if too many appear for comfort, and to keep them clear of weeds.

colours of summer: growing annuals and biennials Half-hardy annuals can be sown outdoors in late spring as a rule, but then may start to flower so late in the summer that they make little effective contribution to the garden. If sown earlier out of doors they either fail to germinate because soil temperatures are too low, or they germinate but are then at risk from spring frosts which can continue well into May in many parts of Britain. To overcome these twin hazards they are sown in a controlled climate, in a greenhouse, frame or well-lighted room, in which a temperature of between 13-18°C (55-65°F) can be maintained. The seedlings are grown on in this same temperature range until it matches that outdoors, usually some time in late May or early June, when it is safe to plant them wherever they are required.

Tender annuals are those that are rarely happy in the open in the British Isles except perhaps for a few weeks in summer or in the mildest, mainly maritime districts. They are essentially greenhouse plants, to be grown throughout their short lives in a controlled climate in temperatures generally several degrees higher than those that suit the half-hardy kinds.

Biennials and monocarpic plants resemble annuals in dying after they have flowered and produced ripe seed but differ in the time they take to do this.


What Makes Them Grow?

Most annuals are sun-lovers though a few will succeed in shade. All like reasonably well drained, moderately fertile soil. In poor, dry soil they are unlikely to make sufficient growth to give a good display. Many hardy annuals have a fairly short flowering season but half-hardy annuals and the half-hardy perennials, grown from seed as if they were annuals, usually continue in bloom for much longer.

By contrast, hardy annuals are natives of temperate regions where the growing season is much shorter and they must hurry to ripen their seeds before the autumn arrives to destroy them. This gives half-hardy annuals, such as petunias, French and African marigolds, scarlet salvias (Salvia splendens), Begonia semperflorens, antirrhinums and verbenas a special value in that they provide colour in the garden over a long period.

Annuals do not require much care once they are planted out. They suffer little from pests and diseases and rarely need to be sprayed. Plants look tidier and continue to flower longer if faded flowers are regularly removed. Weeds should be kept under control so the annuals have no competition.

Some hardy annuals spread freely by self-sown seed. Whether it is wise to let them do so depends a good deal on whether they are species or hybrids. Species, if not highly developed by selection, breed fairly true to type from seed and so self-sown seedlings can be accepted as a welcome bonus. Garden hybrids tend to break up and produce inferior plants; the deterioration continues with each succeeding generation.

Home-saved seed presents similar problems. The more highly developed the variety, the less likely it is to produce seedlings of its own character and quality. Worst of all in this respect are the F1 hybrids which have to be remade every year from parent plants which are never distributed by the raisers. So if you expect the seed from your pink petunias to give pink flowers next year, you could be sadly disappointed.


05. April 2011 by admin
Categories: Annuals, Bedding Plants, Plants | Tags: , | Comments Off on Colours of Summer: Growing Annuals and Biennials


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