How to grow annuals from seed

Annuals and biennials are grown from seed and increased by the same method. If you save seed from your own plants, and use it the following season, remember that the resultant plants will not necessarily be the same in flower, habit of growth or size as the parent plants. Annuals, whether hardy or not, mostly do best and flower best in sunny places, and on the whole they prefer well-drained soil. Although the soil should be prepared in the usual way before sowing or planting, heavy soils should not be made too rich, otherwise the plants will run to leaf at the expense of the flowers – and of your display. Be light-handed with manure and fertilizers when you are preparing the soil and you will get better results.

Seed of annuals is sown in a prepared seed-bed outdoors in spring if they are hardy or, if they are half-hardy, sown in boxes, trays, pots, pans or other containers filled with suitable compost, and placed in warmth, i.e., a temperature of at least 16°C (60°F), preferably 18-21°C (65-70°F) under glass.

Once the seeds have germinated, the seedlings can be treated in two different ways. Those sown outdoors should be thinned as soon as the first true leaf has appeared, or as soon as they are large enough to handle, so that they have a spacing a quarter of the final one. When the leaves of adjacent plants are touching, thin to half the final spacing, and repeat to leave the remaining plants at their final distance from one another. If time is pressing, bigger gaps than those suggested can be left each time, to eliminate one of the stages.

Seedlings sown with protection are pricked out when large enough to handle, allowed to grow slowly, and gradually hardened off before being planted outdoors when frost is unlikely. If these half-hardy plants come on too quickly after pricking out, while the weather remains cold, they can be kept going without a check either by liquid feeding, or by moving into 5-cm (2-in) pots.

Once the plants are well on the way to flowering, there is little that need be done to keep them growing; all the work goes into raising them, and strong healthy seedlings will remove most of the possibility of future backaches. The taller ones will need some sort of support with twiggy brushwood or canes put in when the plants are about 15 cm (6 in) tall.

In the early stages, especially with outdoor-sown annuals, weeding will be essential, as the weeds will germinate just as, if not more, freely than the cultivated plants. As the latter get larger, however, space for weeds will gradually vanish. Keep an eye open for slugs and snails, which are likely to decimate patches or rows systematically on successive nights. Also watch for birds, especially sparrows tweaking the seedlings out of the ground. If the spring is cold and dry, cover the seed-bed and/or the seedlings with the new slitted orange polythene sheet which keeps warmth and moisture in, without stunting the seedlings. As they grow, the sheet, being very lightweight, lifts at the same time. Use it on planted-out half-hardy plants, too, to forestall trouble from late May, or even June, frosts.

Water well in dry or hot summer weather; if you have time, take off dead flower-heads to encourage further production and prolong the display, unless you are saving seed, or would like the plants to self-seed.
At the end of summer or whenever flowering seems at last to have come to a halt, fork up the remains of stems and leaves and dispatch them to the compost heap.