Sowing half-hardy annuals
Half-hardy is such a funny term of describing how a plant copes with cold. Technically it means that they will only manage a touch of frost and then they will turn up their toes. (Tender plants won’t tolerate any at all.) These are plants that come from hot, winter-less places in the world and it might be my imagination, but they do seem to bring a touch of exotic glamour to a vase.
My favourite HHA’s
Cosmos
Nicotiana (I have fallen for N. ‘Bronze Queen’)
Tagetes
Cobaea
Nasturtium
Rudbeckia ‘Sahara’ (technically a tender perennial)
Zinnias and Cleome are also half-hardy annuals but I find them so ugly, so I don’t grow them. You’ll have to ask google about growing those ones I’m afraid.
When to sow
Half-hardy annuals are fast to grow and quick to flower. Because of their dislike of cold, you will need to wait until spring to sow them, although you can steal an extra few weeks on the season by starting the seeds under cover. If I am using a greenhouse and a heat mat, I get sowing HHA’s towards the end of March. (A kitchen windowsill will do almost the same, but plants will get leggy if they are left too long, so don’t get sowing if your last frost date is still some way away.
How to sow under cover
You will need
/ Peat-free compost
/ Either small pots (for larger seeds such as sunflowers) or module trays
/ Labels
/ Seed
Fill a tray or your pots with compost. Shake and pat to level a bit but do not compact the soil. Aim for the texture of a Victoria sponge.
For larger seeds, poke two seeds half a centimetre below the surface of the compost. For tiny seeds, just scatter a tiny pinch in each cell. Be careful, Nicotiana seeds are tiny. Cover with vermiculite or a tiny bit of seed compost and then put the pot or tray in water for half an hour to water from below.
Place in a warm spot and protect from drafts and scorching direct sunlight.
Once seeds have sprouted, wait until two pairs of leaves form. Carefully pot up each seedling into a pot filled with sieved compost.
When you are absolutely sure the risk of frost has passed, start to harden them off. This just means putting them out on warm, sunny days, and bringing them in at night or when the days are particularly chilly.
After a week or so, plant them outside.
Direct sowing
You can also sow half-hardy annuals directly outside in late spring or early summer once frosts have passed.
If you want to go the direct sowing route, just scatter around towards the end of April, lightly cover and gently water.
I know, so much easier, but you do run the risk of slugs.
Pinch them out
As counter intuitive as it is, if you want sturdy plants, long, abundant, elegant stems, you need to pinch them out.
Once the plants are 4–6 inches tall, pinch out the central growing tip, just above a leaf joint, leaving just two or three leaf nodes. This will encourage the plant to branch vigorously from the base.
Growing on
Keep the plants watered in very dry spells and make sure they aren’t surrounded by weeds. They should be flowering by July.