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How to sow half-hardy annuals
- BBC Gardeners' World Magazine
Published: Monday, 21 October 2019 at 2:40 pm
Find out how to sow half-hardy annuals, such as cosmos and zinnia, in our step-by-step guide.
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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.
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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.
In the above video guide, Monty Don shows you how to fill any gaps in your borders with half-hardy annuals, which will provide colour through to the first frosts.
Here's how to sow half-hardy annuals:
You Will Need
- Seed tray
- Multi-purpose, peat-free compost
- Half-hardy annual seeds
- Vermiculite
Step 1
Sowing the seeds in modular trays
Fill a tray with 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.
Step 2
Pricking out the young seedlings
Once seeds have sprouted, wait until two pairs of leaves form. Transplant each seedling into a 7cm pot filled with sieved compost.
Step 3
Watering in the young seedlings
Water well after transplanting and keep the pots in a warm, bright place. Avoid exposure to bright sunlight, which can scorch the young leaves.
Step 4
Growing on young cosmos plants
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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.
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.
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