It may seem rather a long way off to be sowing summer-flowering plants in autumn, but the forward planning will be rewarded by an impressive early display. Many annuals can be sown in autumn and will overwinter successfully.
Autumn sowing is suitable for annuals (plants which are sown and flower and die in one year) that tolerate frost. Some of these annuals can be sown directly in the ground, and will withstand most frosts. Others are not quite so robust – they can be direct sown, but covered with cloches or horticultural fleece when frost is forecast. Alternatively, they can be sown in pots and kept frost-free over winter.
The benefit of sowing in autumn, and not spring, is that you'll have a much earlier flowering display.
This technique is not suitable for half-hardy and tender annuals. Unless you have access to a heated greenhouse, these are best sown in spring.
When to sow hardy annuals
Early autumn is best, usually September in the UK, when the soil is still warm.
How to sow hardy annuals
This method involves sowing directly into the soil, either by broadcasting (scattering seed over the soil surface) or drilling (sowing more precisely in rows). No matter which method you choose, prepare your soil bed in the following way for the best results:
- Make sure the area to be sown is weed-free
- Dig over the soil to a spade’s depth, rake it over and firm
- Plan the area to be sown by sprinkling grit or sand on the soil or score the ground with a cane to mark out sowing areas. Decide what should go where according to height, habit and flower colour
- It is important not to sow into a soil that is too rich, since this may encourage leafy growth at the expense of flowers, so avoid using fertiliser
- Either broadcast or drill the seed as follows:
Scatter seed thinly over the plots and cover lightly with soil or compost. Aim for a gap of about 0.5cm (¼in) between seeds. Water well with a watering can fitted with a fine rose.
Dividing the bed into irregular patches and sowing into drills (shallow grooves) running in offset directions gives a more natural appearance as plants mature. Space drills 15–45cm (6-18in) apart (depending on the eventual size of the plants). Sow seeds 0.5cm (¼in) apart in each drill, and rake soil over the drills to cover them. Water well with a watering can fitted with a fine rose. As a precaution, beds can be covered with horticultural fleece during cold snaps.
Annuals can also be sown under cover at 18°C (64°F), reducing to 15°C (59°F) after germination. Grow them on into small plants, harden them off for overwintering in a cold frame or unheated glasshouse, and plant them out the following spring.
Suitable annuals to try
Hardy annuals requiring no protection
These hardy annuals may require protection in northern parts of the UK, or even in southern parts if winter is harsh. Keep an eye on the weather, and if hard frosts are forecast, protect sowings with cloches or horticultural fleece.
Ammi majus: Creamy white lace-like flowers in summer and ferny foliage.
Calendula officinalis: Single or double daisy-like flowers in shades of orange, gold, cream or yellow from summer to autumn.
Centaurea cyanus (cornflower): Dark blue daisy-like flowers from late spring to mid-summer.
Limnanthes douglasii (poached egg plant): Numerous cup-shaped yellow-centred white flowers from summer to autumn.
Linum grandiflorum (flax): Saucer-shaped rose-pink flowers with dark eyes in summer.
Hordeum jubatum (squirrel tail grass): Long silky tufted flowers on grassy stems from early to mid-summer.
Nigella damascena (love-in-a-mist): Saucer-shaped pale blue flowers surrounded by a ruff of ferny foliage.
Lunaria annua (honesty): White or pale purple flowers in late spring and summer followed by flat, round, silvery seedpods.
Papaver commutatum, P. rhoeas, P. somniferum (corn and opium poppies): Large cup-shaped blooms with black centres in shades of orange, red, pink, mauve and white.
Briza (quaking grass): Nodding spikelets of flowers that move in the wind with grassy foliage.
Consolida (larkspur): Delphinium-like spikes of flowers in shades of pink, blue or white.
Hardy annuals needing some protection
These hardy annuals will need some protection from frosts, even in milder parts of the UK. Cloches and horticultural fleece should do the job. In colder parts of the country, consider sowing these in pots under glass.
Lathyrus odoratus (sweet pea): Fragrant climber with flowers in most colours except yellow from summer to early autumn; best sown in pots.
Eschscholzia (Californian poppy): Cup-shaped flowers of yellow, orange, red or white in spring or summer, with ferny foliage.
Gypsophila elegans: Clusters of numerous tiny white or pink flowers on slender stalks in summer.
Lavatera trimestris (mallow): Cup-shaped flowers of pink or white in summer.
Cerinthe major var. purpurascens: Deep purple bell-shaped flowers held in a cluster of dark blue bracts in summer; blue-green foliage.
Salvia viridis (annual clary): Showy pink, purple or white leaf-like bracts in summer.
Matthiola longipetala subsp. bicornis (night-scented stock): Pink, purple or mauve flowers in summer, strongly scented at night.
Orlaya grandiflora: Lacy white blooms produced all summer long.
Nemophila: Saucer-shaped white or blue flowers in summer, with blue spots on the tips of the petals.
Adonis aestivalis: Ferny foliage and cup-shaped red flowers with dark centres in mid-summer.