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How to Sow Cornflowers in Autumn for Bigger Plants in Spring

Rachel is a passionate plantsperson, YouTuber and author living in Ireland. She grows a wide range of hardy subtropical and tropical plants.

Sowing cornflowers in autumn makes for bigger plants and earlier flowers come spring.

Sowing cornflowers in autumn makes for bigger plants and earlier flowers come spring.

Can You Plant Cornflowers in the Fall?

Yes! Autumn sowing cornflower seeds is a great way to ensure an early, colorful display of annual plants. Now you can sow them in spring, but you will get smaller plants that start into flower later. By sowing in autumn, we'll get larger plants that kick into flower earlier.

Cornflowers (Centaurea cyanus) produce pretty balls of cheerfulness that flower all summer long, and while they come in shades of white, pink, and almost black, mostly it's the iconic blue that we all know. They're really useful for filling any gaps in your flowerbeds.

Can You Grow Cornflower in Winter?

No, but you can start your seedlings in autumn and tend them through the winter until spring arrives and they can be planted out. In other words, cornflowers are hardy annuals, and this means that they tolerate more cold than other annuals, but that doesn't mean they'll survive the winter without proper tending.

There are a few things you need to do to ensure that seedlings can grow through fall and winter so that they're ready to be planted out in spring.

Cornflowers are easy to sow and grow in fall, but remember—autumn sowing in the house is not a good idea.

Cornflowers are easy to sow and grow in fall, but remember—autumn sowing in the house is not a good idea.

How to Sow Cornflower Seeds in Autumn

You'll need a greenhouse, a cold frame or a sheltered outdoor position for autumn sowing. You could alternatively sow your cornflowers in drills outdoors in autumn, but be aware—autumn sowing in the house is not a good idea.

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  1. First off, fill a seed tray with seed compost. Use a proprietary seed compost, or if you don't have any, mix some fine potting compost with a little horticultural sand.
  2. Firm your mix down a little, then place the seed tray in water and leave it until it has soaked the water up.
  3. Now, remove the tray from the water and allow to drain.
  4. Pour your seeds into a little bowl. In the demo video above, you can see what cute things they are! And the good news is that they're big enough to see, which makes sowing easier.
  5. Sow your seeds one or two per cell or about an inch apart. You may need to prick out seedlings later, but that's a job for spring.
  6. Try to sow your cornflowers thinly now because you shouldn't disturb them again in winter. (If you do decide to separate seedlings when the weather is cold, their vulnerable roots will be damaged and the winter cold will finish them off.)
  7. Cover your seeds with a layer of vermiculite, as this will let light through.
  8. Finally, place a lid on your tray or a plastic bag over your pot. Germination will normally happen quickly, sometimes taking a mere five days.
  9. When your seedlings poke up, immediately remove the lid or plastic bag from them. In this way, they'll quickly acclimatize to more air, cooler temperatures and less moisture, and they'll grow strong.
  10. Once seedlings are uncovered, check their moisture levels regularly and water them lightly whenever the mix is feeling dry. Try not to wet the top growth when watering.

When to Plant Out Cornflower Seedlings

These seedlings may not do a lot until spring, but then they'll really get going. At this stage, I'll prick them out and plant them outdoors when all danger of frost has passed.

Cornflowers prefer poor soil and full sun, and they need no fertilization for months of flowering color. Happy growing!

More About Sowing Seeds in September

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© 2021 Rachel Darlington

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