Easy to grow and fast to flower, hardy annuals can be unrivalled for bringing summer colour to the garden. They are usually grown from seed sown outdoors in spring when the soil is warm and moist then weeks later they start into flower finally setting seed and dying by the end of summer. However, there are two other methods you can use to give a wonderful display of annuals in flower.
Sowing in spring
Step one
Prepare the soil for seed sowing in spring by digging over, removing weeds and adding organic matter if necessary, then rake it to create a fine tilth (a fine, crumbly top) . Sow the seed in drills as it’s easier to identify stray weed seedlings as those growing outside the drill. Use a garden line and draw hoe to create a shallow furrow for sowing.
Sowing in spring
Step two
By April the soil is warm and moist from frequent showers, but if dry water along the base of the drill before sowing. Don’t sow the seed too thinly as there will be losses and you can thin the seedlings once they germinate. Cover lightly and water the soil using a fine spray.
Sowing in spring
Step three
By mid May all the seedlings will be growing well. Although it seems a waste, thin the seedlings to a 20-30cm (8-12in) spacing to give the remainder space to grow into sturdy plants full of flower heads. Flowering will begin by mid June depending on the variety.
Sowing in autumn
Step one
If you have clear beds by September, you can get ahead and sow seed in late September where you want it to flower, and providing the plants survive the winter they will burst into flower by late spring. Prepare the soil and sow the seed as you would in spring.
Sowing in autumn
Step two
The soil will still be warm enough in many areas for the seeds to germinate and develop several leaves before winter sets in. You can give them some extra protection by spreading a couple of layers of fleece over the seedbed. By April, those that have survived the winter will be growing well.
Sowing in autumn
Step three
Flowers will start to appear by early to mid May depending on the weather, here Centaurea cyanus Polka Dot series, and will continue for several weeks, especially if the flowers are picked regularly.
Sowing in plugs in autumn
Step one
Some hardy annuals aren’t quite so hardy as others and won’t necessarily tolerate the cold and winter rains, but you can still sow in seed in autumn into plug trays and then protect the seedlings in a cold frame or greenhouse. They won’t need much heat, just a well lit, frost free environment.
Sowing in plugs in autumn
Step two
Plant out the plugs in spring (March- April) once the soil warms up, but give them a few days outside in a sheltered position to harden off beforehand. Water the plugs well before planting and again once in position so that they establish well.
Sowing in plugs in autumn
Step three
The plants will grow quickly and soon start to flower, especially if the weather in the following weeks is favourable.
Hardy annual demonstration
A demonstration of all three methods was run at RHS Garden Hyde Hall in 2010. The hardy annuals sown outdoors in autumn didn’t all survive but those that did flowered first in spring (left) and then started to form seedheads. The plug plants grown from an autumn sowing grew very quickly and were flowering well by mid June (right) with those sown outdoors in spring flowering slightly later (centre).