A hardy annual lives for one year and shrugs off frost

A hardy annual is a plant that grows, flowers, sets seed and dies within one year, and can survive frost while it does. The “annual” part is its life span. The “hardy” part means you can sow it outside before the last spring frost, rather than waiting until after.

That makes hardy annuals some of the easiest plants to grow. Scatter the seed in spring, and you’ll have flowers by summer.

Hardy, half-hardy and tender

Type	Frost	When to sow	Examples
Hardy annual	Survives frost	Outside, from a few weeks before the last frost; some in autumn	Calendula, sweet peas, cornflowers, borage, phacelia, nigella
Half-hardy annual	Damaged by frost	Indoors before the last frost, or outside after it	Cosmos, rudbeckia, nicotiana
Tender annual	Killed by any frost	Indoors, or outside once the soil is warm	Zinnias, French marigolds, nasturtiums, sunflowers

“Hardy” is relative. Calendula copes with around -10 °C and sweet peas around -5 °C, enough for a typical spring frost, but not for a severe winter without some protection.

Vegetables are annuals too

The same terms apply in the vegetable garden. Lettuce, peas, broad beans, radishes, spinach and rocket behave as hardy annuals. Tomatoes, beans, courgettes, sweetcorn and basil are tender annuals, which is why they wait until after the last frost.

Some vegetables are really biennials, such as carrots, beetroot, onions and parsnips. They make roots or bulbs in the first year and flower in the second, but we harvest them before they get that far.

When to sow hardy annuals

Spring. Sow outside from about four weeks before your last frost, once the soil is workable and not cold and wet. Most will keep going if sown every few weeks until early summer for a longer display.

Autumn. Many hardy annuals can be sown in early autumn, about six to eight weeks before the first frost. They make small plants before winter and flower weeks earlier next year. Sweet peas are often sown in pots in a cold frame in autumn for this reason.

How to sow them

1. Choose a sunny spot. Most hardy annuals don’t need rich soil, and too much feeding gives leaves rather than flowers.
2. Rake the soil fine and remove weeds.
3. Mark out drifts with sand and sow in short rows within each drift. Straight rows make it easy to tell seedlings from weeds.
4. Cover lightly and water.
5. Thin the seedlings to the spacing on the packet once they’re big enough to handle.

Hardy annuals for the veg garden

Some earn a place among the vegetables. Calendula and borage draw in bees and hoverflies. Phacelia is a fast green manure that bees love. Sweet peas can share a frame with climbing beans. Nasturtiums, though tender, trail around squash and act as a decoy for blackfly.

For sweet peas in detail, see sowing sweet peas in autumn, and for more on which plants help each other, the companion planting guide.