Cosmos

How to sow half-hardy annuals

Find out how to sow half-hardy annuals, such as cosmos and zinnia, with the help of our step-by-step guide.

Do it:

Mar, Apr

Takes just:

15 minutes

At its best:

Jun, Jul, Aug, Sep

Half-hardy annuals are quick to flower and provide a burst of colour in summer borders and pot displays. Many varieties sown indoors by March or April will start to flower as early as June.

Discover 10 half-hardy annuals to grow

To give them as long a flowering season as possible, sow seeds early so that plants have plenty of time to establish before planting out in early summer. They are very sensitive to frost, so must be sown under cover, and only planted out once all risk of frost has passed.

Here's how to sow half-hardy annuals.

You will need

  • Seed tray
  • Good quality compost
  • Half-hardy annual seeds

Advertisement

Fill a tray with seed compost, then sow a tiny pinch of seeds in each cell. Cover with vermiculite, water and place the tray in a propagator in a warm spot.

Once seeds have sprouted, wait until two pairs of leaves form. Transplant each seedling into a 7cm pot filled with sieved multi-purpose compost.

Water well after transplanting and keep the pots in a warm, bright place. Avoid exposure to bright sunlight, which can scorch the young leaves.

Many varieties sown indoors by March or April will start to flower as early as June.

When all risk of frost has passed, move the plants to a cold frame or patio, bringing them in at night. After a week you can plant them outside.

Advertisement

Seedlings

Sowing half-hardy annuals outside

You can also sow half-hardy annuals directly outside in late spring or early summer once frosts have passed. Try sowing cosmos, zinnia, nasturtiums and French marigolds this way.

Discover more ideas and inspiration

Related content

Creating a summer pot

How to sow sweet pea seeds

How to sow salad seeds in guttering

Related offers

HALF PRICE

Half-price acers

Enjoy spectacular foliage that changes colour throughout the seasons with this lovely collection of acers. You'll get three trees for just £14.99 (half price) with this offer.

Use code: RGW128

Order now

SAVE 20%

Subscriber only content

Save at Blooming Direct

Save 20 per cent on everything at Blooming Direct, including roses, shrubs, grow-your-own fruit and veg, bedding, bulbs, a range of accessories and more.

Unlock now

SAVE 20%

Save 20% at Bakker

Save 20 per cent on the entire range a Bakker, including spectacular Rhododendron 'Polaris' (pictured) and much more. Please enter code at checkout to claim your discount on any order over £20.

Use code: BBC20OFF

Order now