If you crave breath-taking displays of flowers that form a blaze of colour from summer through to autumn, then you'll love growing annuals. Annual plants grow, flower, set seed and die in the space of one season. A vast number of the UK's most cherished bedding favourites – especially those that adorn hanging baskets, window boxes, containers and flower beds during the warmer months – are annuals, while many veg plot staples fall into the category, too.
Because annuals are quick-off-the-mark and flower prolifically, they make ideal gap fillers and you won't have to wait long until they bloom. Most will thank you for a sunny spot and well-drained soil. To enjoy the best displays, you’ll need to water and feed regularly during the growing season. Annuals are ideal for folk who are new to gardening, because they’re easy to raise from seed and produce spectacular results with little requirement for horticultural know-how. However, they must often be regularly dead-headed to prolong displays, or flowering will be cut short if plants are allowed to fulfil their mission and run to seed.
Although gardeners only benefit from one season of enjoyment, annuals are extremely cheap to raise, and different displays can be planned every year. At the end of summer, these hard-working plants can be added to compost heaps to be turned into next season's soil improver.
See our full range of annuals here.
What are half-hardy annuals?
Half-hardy annuals are tough enough to spend most of their mature lives outdoors but will not tolerate cold temperatures or frost. For this reason, these tender plants are usually raised from seed in warm conditions indoors, before being planted out into gardens after all risk of frost is over – that’s commonly late May in the south or early June in cooler, northern regions.
Classic examples of half-hardy annuals include French and African marigolds, petunia, nicotiana, aster, zinnia, cosmos and phlox. Half-hardy annuals need warmth to germinate, which is why sowing indoors or in a heated greenhouse is the most popular method of germination. Some can be direct-sown outdoors where they are to flower from late May, once the soil has warmed up, but the late start means you’ll get a shorter season of flowers. If you’ve sown half-hardy annuals under cover, young plants will need hardening off, a process of acclimatisation to get the plants used to cooler growing conditions outdoors. It’s a simple procedure where plants are placed outdoors on mild days and brought back under cover before temperatures drop at night. Hardening off takes around a fortnight.
You’ll need to take care during the first few weeks after planting out, as young growth is particularly appetising to slugs and snails. Using organic slug pellets or beer traps sunk into the soil close to vulnerable plants will help to keep molluscs at bay.
What are hardy annuals?
Hardy annuals also grow, flower and die within the space of one year but they’re tougher than half-hardy annuals, as they tolerate lower temperatures or light frosts. Depending on your choice of seed, hardy annuals can be sown in spring or autumn. Hardy annuals sown in spring will flower later than plants that have been started in autumn. However, some will need the protection of a cloche, or covering with horticultural fleece, if a heavy frost is forecast. If you’re sowing in spring, many hardy annuals can be direct-down on light soils where they are to grow and flower, from late March into May, eliminating the need to raise plants indoors early in the season. Some of the most popular examples of hardy annuals that are commonly sown in spring include sunflower, poached egg plant, cosmos, calendula (pot marigold) and nasturtium.
Autumn-sown hardy annuals benefit from a head start, resulting in bigger, stronger plants that reward gardeners with earlier displays of flowers next season. Don’t worry if they put on little growth over winter – that’s normal – and rest assured that their roots will still be developing. Those cottage garden favourites sweet peas are a good example of hardy annuals that can be sown in autumn or spring. You’ll enjoy superb blooms regardless of when seed is sown, but an autumn sowing (usually under glass) offers a host of benefits including vigorous growth, longer stems, bigger flowers and, crucially, flowers bursting into bloom earlier in the season.
Frequently Asked Questions
Why are gardeners told to treat some half-hardy perennials as half-hardy annuals? Certain bedding favourites, such as the busy Lizzie, are classified as half-hardy perennials but will be wiped out by cold weather in autumn. That’s why they’re best treated as annuals and composted when plants are past their prime at the end of the season.
What kit do I need to sow annuals indoors? Annuals are easy to raise from seed. All you need is a pot or seed tray, a propagator, plant labels and a good quality seed and cuttings compost.
I don’t want to use slug pellets, even if they’re organic. How can I protect vulnerable annuals? Create a physical barrier around susceptible plants using crushed egg shells or shop-bought slug barrier granules. Molluscs dislike slithering over these rugged surfaces.
How can I stop annuals in containers being decimated by slugs and snails? Fix copper tape around pots, just below the rim. The tape emits a tiny electrical charge which encourages molluscs to slither off elsewhere.
Can I grow annuals on heavy soils? Annuals prefer light soils that warm up quickly in spring (whereas heavy soils remain wetter and colder for longer). If soil conditions are too heavy, and prone to waterlogging, grow annuals in pots, window boxes or hanging baskets instead.
How do I direct-sow annuals outdoors? You’ll need to prepare a seed bed that’s free of weeds and large stones, and raked to a fine tilth. Whether you broadcast seed (scatter it over the soil surface) for a more informal look, or sow in straight drills, depends on what is being sown. Seedlings may later need thinning out to give young plants enough space to grow.
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