Sowing half-hardy annuals in mid spring

Sowing Half-Hardy Annuals in Mid-Spring

Half-hardy annuals should be sown in mid-spring, a bit later than hardy annuals – between the end of March and mid-April.

You can only plant them out after the risk of frost has passed, so you don't want them to get too big too early.

• If they sit in their pots for too long, they will start to decline.
• You want them to go into the ground at their healthiest.

Half-hardy annuals include:

• cosmos
• zinnias
• dahlias (sometimes counted as tender perennials, sometimes half-hardy annuals). Growing dahlias from seed rather than tubers means you can't guarantee colour so they're usually sold as mixes – I'm sowing a mix called 'Bishop's Children'.

These are all perennials in their natural habitat, but we generally grow them as half-hardy annuals.

Half-hardies need about 21°C (70F) to germinate, so should be indoors or on a heat mat in the greenhouse.

Cosmos are a great one to start with as they're really easy to grow and have big, elongated seeds.

How to Sow Cosmos

1. Put seed on surface of pre-watered compost, one seed to each module.
2. Cover with a little sieved compost.
3. Gently firm the seed in with a tamper.
4. Put the propagator lid on and take inside to germinate at 21°C.

Sow Half-Hardies Successionally for Summer-Long Flowering

• Start sowing these at the end of March and sow a batch every few weeks to ensure continual flowering from the beginning of July until the first frosts.
• They're a really easy and good value way to get colour over a long season.

Plant Directory

Cosmos bipinnatus 'Apricotta'

Mexican aster 'Apricotta'

Half-hardy annual

Asteraceae

Cosmos bipinnatus 'Kiiro'

Mexican aster 'Kiiro'

Half-hardy annual

Asteraceae

Cosmos bipinnatus 'Purity'

Mexican aster 'Purity'

Half-hardy annual

Asteraceae

Cosmos bipinnatus 'Rubenza'

Mexican aster 'Rubenza'

Half-hardy annual

Asteraceae

Dahlia BISHOP'S CHILDREN (mixed)

Dahlia BISHOP'S CHILDREN (mixed)

Tender perennial grown as half-hardy annual

Asteraceae