Hardy annuals: sowing in autumn

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.

Title: Hardy annuals

Title: Hardy annuals

Quick facts

Suitable for: Hardy annuals
Timing: Early autumn
Difficulty: Moderate

Suitable for...

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

Direct sowing

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:

  1. Make sure the area to be sown is weed-free.
  2. Dig over the soil to a spade’s depth, rake it over and firm.
  3. 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.
  4. 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.
  5. Either broadcast or drill the seed as follows:

Broadcast

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.

Drills

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.

Protected sowing

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 (bishop's weed): Creamy white lace-like flowers in summer and ferny foliage. Height 30-90cm (1-3ft) and spacing 30-40cm (1ft-16in).
Briza maxima (quaking grass): With creamy-white shimmering spikelets, ideal for dried arrangements. Height 60cm (2ft) and spacing 30cm (1ft).
Calendula officinalis (pot marigold): Slightly aromatic leaves and single or double daisy-like flowers in shades of orange or yellow flowers from summer to autumn. Height 45-60cm (18in-2ft) and spacing 30-37cm (1ft-15in). Centaurea cyanus (cornflower): Dark blue daisy-like flowers from late spring to mid-summer. Height 30-90cm (1-3ft) and spacing 23-45cm (9-18in).
Consolida (larkspur): Delphinium-like spikes of flowers in shades of pink, blue or white. Height 45cm-1.2m (18in-4ft) and spacing 30-45cm (1ft-18in).
Linum grandiflorum (flax): Saucer-shaped rose-pink flowers with dark eyes in summer. Height 30-45cm (1ft-18in) and spacing 10-15cm (4-6in).
Hordeum jubatum (squirrel tail grass): Long silky tufted flowers on grassy stems from early to mid-summer. Height 60cm (2ft) and spacing 30cm (1ft).
Nigella damascena (love-in-a-mist): Saucer-shaped pale blue flowers surrounded by a ruff of ferny foliage. Seedheads make excellent dried arrangements. Height 30-45cm (1ft-18in) and spacing 15-20cm (6-8in).
Lunaria annua (honesty): White or pale purple flowers in late spring and summer followed by flat, round, silvery seedpods. Height 90cm (3ft) and spacing 20-30cm (8in-1ft).
Papaver somniferum (opium poppy): Single or double flowers in shades of deepest purple, lilac, pink and white, some are blotched at the base. Self seeds easily. Height 45-90cm (18in-3ft) and spacing 25-45cm (10-18in).
P. rhoeas (Shirley poppy): Single flowers have a white base and come in shades of scarlet, pink and white. Height 45-90cm (18in-3ft) and spacing 25-45cm (10-18in).
P. commutatum (ladybird poppy): Scarlet flowers have central black ladybird-like blotches. Self seeds readily. Height 45-90cm (18in-3ft) and spacing 25-45cm (10-18in).

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.

Adonis aestivalis: Ferny foliage and cup-shaped red flowers with dark centres in mid-summer. Height 40cm (16in) and spacing 15-30cm (6in-1ft).
Cerinthe major 'Purpurascens': Deep purple bell-shaped flowers held in a cluster of dark blue bracts in summer; blue-green foliage. Height 60cm (2ft) and spacing 30cm (1ft).
Eschscholzia californica (California poppy): Ferny foliage and cup-shaped flowers of yellow, orange, red or white in spring or summer. Height 15-30cm (6in-1ft) and spacing 20-25cm (8-10in).
Nemophila menziesii (baby blue eyes): Saucer-shaped white or blue flowers in summer, with blue spots on the tips of the petals. Height 15-30cm (6in-1ft) and spacing 15-20cm (6-8in).
Lathyrus odoratus (sweet pea): Fragrant climber with flowers in most colours except yellow from summer to early autumn; best sown in pots. Height 30cm-2.5m (1-8ft) and spacing 20-37cm (8-15in).
Linaria moroccana Fairy Bouquet Group (toadflax): Small, snapdragon-like flowers in pastel shades. Height 15-30cm (6in-1ft)  and spacing 7-10cm (3-4in).

Problems

Annuals can suffer problems from damping off when first sown.

They may be damaged by slugs, snails, aphids and powdery mildew as they are growing.


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