Zinnias are beautiful annual flowers that add a merry mark to any garden or windowsill. If you want to grow your own this year, you’ll need to know when to plant zinnia seeds to give them the best chance of blooming.
Timing is everything when it comes to planting seeds, and zinnias are no different. We consider them to be one of the best flowers for raised beds, but you’ll only be able to enjoy them if you sow the seeds at the right time. Too early, and they’re unlikely to survive the frost, but too late, and they won’t bloom in time for summer.
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When to plant zinnia seeds depends on if you’re planting them indoors or outdoors. ‘If you’re sowing them directly in the soil outdoors, you need to wait until the last frosts are over and the nights are warm, which is usually in May or June,’ Chris Bonnett, founder of GardeningExpress says. ‘But if you’re planting the seeds in containers indoors, do it from February to April.’
So, if you’re wanting to house the seedlings on your kitchen windowsill, you can plant the seeds from now up until April. But if you’d rather grow directly in your garden, you’ll need to wait until May at the earliest (if you want to sow your seeds successfully).
Zinnias are extremely sensitive to the cold, so they just won’t bloom if they’re planted outside during winter or early spring. Even if you’re planting seeds in April, it’s best to do it inside when it comes to this annual plant.
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How to plant Zinnia seeds
If you are starting your seeds indoors, fill a seed tray or a 9cm pot with seed compost and lightly water it, then place the seeds on the damp compost.
‘For seed trays, plant two to three seeds per cell, leaving about two inches of space between them,’ Joe Aldworth, gardening expert at The Old Railway Line Garden Centre advises. ‘If using a pot, you should plant seven or eight seeds per pot to provide enough room for germination.’
Gently press the seeds into the compost using the base of an empty pot, then cover with a thin layer of compost and water lightly. Keep the soil moist by watering a few times a week.
Caring for your Zinnia seeds
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To increase your chances of growing beautiful zinnias from seed, you’ll need to help them get as much natural light as possible.
‘Zinnias thrive in a sunny spot that gets direct sunlight for at least 6 hours a day, and they prefer well-drained soil,’ Chris offers.
Temperatures between 21-24°C are ideal, but if you’re sowing your seeds in February, it might naturally be a little colder. Just try and keep the seeds as warm as possible, i.e. away from cold draughts and doors.
‘A heat mat, if possible, or a warm windowsill is an ideal environment for maintaining the necessary warmth,’ Joe says.
‘If you’re growing zinnias from seed, expect to see flowers in about 6-8 weeks,’ says Jenny He, co-founder and CEO of Ergeon. ‘They germinate fast—usually within a week—and once they take off, they don’t slow down. The key is full sun and well-draining soil.’
Once they do start to flower, picking zinnia flowers regularly will help to encourage the plant to keep producing flowers.
What you’ll need to grow zinnias from seed
Mr Fothergill’s 18536 Flower Seeds, Zinnia Jazz
Professional Compost 60l by Jamieson Brothers
Seed Trays Seedling Tray 10-Pack
FAQs
Do zinnias come back every year?
‘Unfortunately, zinnias are not perennial and are usually planted as annuals because of their tender nature and their growth speed,’ Graham Smith MCIHort, gardening expert from LBS Horticulture explains. ‘It is best to grow Zinnias from new, fresh seeds every year, but you can save a few blooms for harvesting.’
So, even if you have success with planting zinnias this year, it’s unlikely you’d get a fresh crop from the same seeds next year.
Now you know when to plant zinnia seeds, will you be seizing the opportunity to grow these beautiful flowers any time soon?
