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How to grow hardy annuals

Val Bourne / 23 February 2016 ( 15 February 2021 )

Annual flowers can easily be grown from seed in trays or straight into the ground. Read our guide to find out how to grow hardy annuals.

Snapdragon, a half-hardy annual
Snapdragon, a half-hardy annual

As a gardener there’s nothing quite as thrilling as sowing a packet of seeds and watching them flower. Hardy annuals, listed under HA in the catalogues, are the easiest seeds of all because they germinate easily without an anxious will-they wont-they wait. 

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What is a hardy annual?

Hardy annuals are plants which can germinate outdoors and will live their entire lifecycle within a year. Annuals positively want to germinate because they need to flower and set seeds before the year ends. In order to accomplish this most produce lots of nectar or pollen to lure in the pollinators, so your garden will be buzzing with activity. They’re also colourful, so extremely useful fillers whether in the border or a vase.

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Annuals and pollinators

Hardy annuals tend to be colourful because they’re out to attract pollinators. They use their colour to attract different pollinators. Blue is very attractive to bees. Orange tend to lure in hoverflies and pollen beetles, whereas white and green are often preferred by flies who make excellent pollinators. Flower structure is also important. Tubular flowers often suit longer-tongued bees.Short-tongues bees like accessible flowers they can land on, or saucers. Hoverflies have small mouths and prefer umbels with cow parsley like flowers. So grow a range.

Pollinators are looking for sustenance. They require sugary nectar, the Lucozade of the insect world, for energy for flight. Often nectar is replenished very quickly in annuals. Borage (Borago officinalis), for example, tops up its nectar supply within minutes so it’s hardly ever without a bee. It’s the classic floating flower for summer drinks, from Pimms to elderflower cordial, but you could equally well use it in salads along with calendula and nasturtium flowers. It’s not a tidy plant, but a patch is always a good thing in midsummer.

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Some annuals, such as Larkspur (Consolida ajacis), have spurs at the back of their flowers and these hold a lot of nectar. Although designed to sustain long-tailed bees, often short-tongued bees rob the nectar by biting into the back of the spur. Pollinators are meant to visit the front end of the flower and as they do so they pick up pollen on their bodies and heads. This tends to be sticky and they distribute it as they enter another flower, cross pollinating as they go.

Pollen is a protein-rich substance that’s vital for breeding and raising the next generation. Some flowers, such as poppies, only produce pollen and no nectar. They’re still popular, particularly with hoverflies who need lots of pollen to breed. When choosing varieties go for open-centred easy-access flowers rather than doubles.

Sowing hardy annuals directly into the ground

When to sow

Many annuals are best sown straight into the ground rather than in seed trays, because they have tap roots. However the soil must be warm so the best time for fail safe results is early May. Sow too earlier and you’ll get patchy results so it’s important to get your timing right. Think early summer rather than spring for sowing into the ground.

How to sow

Prepare the soil with a rake, so that there’s a fine layer, and water the ground well before sowing. Scatter the seeds on the surface and lightly cover with soil. Add some netting and sticks, to keep away cats. If it’s dry water the seeds in the morning if possible.

Sowing hardy annuals in trays

When to sow

The vagaries of the British climate can make sowing direct a hit and miss affair in cold springs. It is possible to sow most annuals in trays in early March under unheated glass, such as an unheated greenhouse or windowsill.

How to sow

Thinly scatter the seeds, and then prick them, once they have a pair of true leaves as well as round seed leaves, out into 3in, or 9mm pots, and plant them out in late May.

Once the seeds germinate and get a pair of true leaves above the rounded cotyledons (or seed leaves) you can prick them out into modular (6 x 4) trays and grow them on under glass until they root through the module. Handle the small seedlings by their two first leaves, not the stems. This takes four weeks on average.

These modules can be potted on into 9cm pots to make larger plants, or the modules can be planted outside. but they must be hardened off because plants grown in a greenhouse are soft and will get slug damaged. Place them outside in the day in an airy place and this will toughen them up.

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HHA, or half-hardy annuals

If you see HHA on a packet it means Half-hardy annual so sow it from mid-April onwards when it’s warmer. Many HHA plants, such as cosmos and zinnia, flower better once the days begin to shorten so they are often magnificent in autumn.

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Collecting annual seeds

Most annuals set seeds prolifically and these seeds can be collected and stored for next year, so they offer good value. Just leave some of your plants to get on with it from August onwards, and seeds will appear. Once they do, wait for a fine, dry day and then go an collect them. Dry them on saucers, add a label, and then packet them up and place them in a tin in the shed. 

Deadhead the rest of your plants though, because this will keep them in flower for longer.

Hardy annual flowers

Hardy annuals for direct sowing only

These resent pricking out and are best sprinkled where they are to flower.

Ladybird poppies (Papaver commutatum)
A red and black short poppy with good foliage. Allow this to self seed and new seedlings will appear in autumn. These will make robust plants. If seedlings do not appear, rake over the soil because poppy seeds need disturbed soils and good light to germinate. Buried seeds lay there.

Shirley poppies (Papaver rhoeas)
These are selected forms of our native red filed poppy, but with pale edges, and they were originally raised by the Revd William Wilkes who came from Shirley near Croydon. Thompson & Morgan’s 'Angels Choir Mixed’ is a more- double form that still has pollen-rich stamens.

Opium poppies (Papaver somniferum)
This produces too much seed, so do remove most of the heads after flowering. The doubles still set seed and their flowers ( although not so insect friendly) last far longer. ‘Summer Fruits’ from Thompson & Morgan is a good mixture.

Bells of Ireland (Moluccella leavis)
A spike of apple-green bells, heavily embossed in veins, make this highly adored by flower arrangers. Prickly to handle and can be dried.

Pot Marigold (Calendula officinalis)
Bright-orange annuals popular with all insects, these have large crescent-shaped seeds that are best sown directly. My favourite is the mahogany-centred ‘Indian Prince’ from Mr Fothergill’s.

Hardy annuals to grow under glass

The following can either be sown direct or raised under cold glass. If you don’t have a greenhouse order plug plants, or seedlings.

Clary sage (Salvia viridis ‘Blue’)
This foot-high annual has tiny flowers surrounded by showy bracts that give a long display. There are mixtures in sugar-pink combinations of pink, white and blue, but this all-blue mixture (from Sarah Raven) is adorable. do not deadhead and sow direct.

Blue Cornflower (Centaurea cyanus)
The best colour for insects and Red-tailed bumble bees (Bombus lapidarius) seek out this flower. It is best raised in pots, because you can get large plants and, if you deadhead, this will carry on.

Ammi visnaga
A white umbel with sturdy stems and carrot-like foliage and a white starry dome of flowers. Best sown direct in spring, but you can raise this under glass too.

Snapdragon (Antirrhinum majus)
The simple snapdragons, such as the maroon and white ‘Night and Day’ and the all-white ‘The Bride’, make good sturdy annuals and they often self seed, although not worryingly so, and flower late. Once the first spike fades remove it and more flowers will appear. Raise under glass in trays and then prick out.

Larkspur (Consolidago ajacis)
This spike is very welcome because it provides vertical accents. The main colours are blue, pink and white. ‘Gentian Blue from Thomspon & Morgan works well among oranges. Sow direct.

Rudbeckia hirta
Some can struggle to do well in the UK and ‘Prairie Sun’ can be a failure. ‘Indian Summer’ (from Suttons) is the only AGM winner but it’s a large plant and needs space. Raise under glass and prick out into modular trays.

Scabious (Scabioisa atropurpurea)
The pincushion flowers of scabious, held on long stems, are perfect for cutting and will last for several days in water because they consist of lots of tiny flowers surrounded by pretty florets. Scabiosa atropurpurea, which sometimes overwinters, comes in many colours including the soot-black ‘Ace of Spades’ (Thompson & Morgan) and, unlike most dark flowers, it never look sombre because its spangled with white stamens. The Ribena-coloured ‘Burgundy Blue’, ’Salmon Pink’, White and ‘Dark Blue’ are single colour strains and these are always better than mixtures of colours because germination times often vary. It’s quite possible to end up with just the fastest germinator rather than a true mixture. Highly attractive to bees, but forms vary. Raise under glass and prick out into 9cm pots or modular trays.

Scabious (Scabiosa caucasica)
This Scabious has larger flowers on shorter stems and there are far fewer of them, but fields of them were once grown for the cut flower trade before the advent of flown in flowers. S. caucasica mostly comes in shades of soft-blue and white and the centres of the flowers have green buds so they’re stunning in a vase. Chiltern Seeds have ‘Perfection White’ and ‘Perfection Blue’. You could also try a smaller-flowered scabious with rich-blue flowers named ‘Oxford Blue’.

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The opinions expressed are those of the author and are not held by Saga unless specifically stated. The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.