Asking when to plant sunflower seeds? The happy blooms of sunflowers bring blazing hot color to the backyard from July into October.
The three main types – annual helianthus, perennial helianthus, and tithonia – are all native to the Americas, and once you’re in the know about how to grow sunflowers, all that remains is to get the timing right and these beauties will brighten borders and add impressive height. On top of that, many make great cut flowers and attract wildlife.
Our guide has all the details you need about when to plant sunflowers of each type plus expert advice to ensure these desirable blooms thrive in your yard.
When to plant sunflower seeds
The answer to when to plant sunflower seeds depends on their type. Annual helianthus and tithonia can be sown under cover in March or April, or sown direct into soil outside in late spring or early summer. Meanwhile, perennial helianthus can be planted into borders in spring or fall.
Annual helianthus – especially the giant yellow varieties – are fun for children to grow. The seeds are big, so even toddlers can manage to plunge them into the ground. If you have room against a wall or hedge, why not hold a family sunflower competition to see who can grow the tallest?
The stylish dusky-pink and claret-colored annual helianthus and bold-orange tithonia are worth contemplating among your flower bed ideas to fill gaps at the back, as well as for brightening vegetable garden ideas, and the yellow perennial forms (such as ‘Lemon Queen’) are superb border plants.
When to plant annual sunflower seeds
Opting for annual sunflowers, such as the colossal ‘Russian Giant’ or the stylish terracotta ‘Earthwalker’? The answer to when to plant sunflower seeds like this is that they can be sown under cover in early spring. Alternatively, sow direct later in the season.
Sow under cover
Helianthus annuus is a half-hardy annual, so it can be sown under cover (for example, in a greenhouse or cold frame or on a bright windowsill) in March or April in order to produce flowers earlier in the year. Sow into seed trays or modules and then transplant seedlings into individual pots once they are big enough. When the plants are 12in (30cm) tall, they can be planted outside.
Annual sunflowers can be sown direct into soil outside between mid-April and mid-June in well-drained soil in full sun. ‘Sunflowers perform best when direct sown outdoors two to three weeks after the last average frost date or when the temperature of the soil has reliably warmed up, as sunflowers do not like cold,’ says Shannie McCabe, horticulturist for Baker Creek Heirloom Seeds.
When to plant perennial sunflower seeds
Going for perennial sunflowers? Perennial helianthus, such as golden ‘Capenoch Star’ and ice-cream-colored ‘Lemon Queen’, can go into the ground in spring or fall.
In spring, plant perennial sunflowers at the back of sheltered borders in full sun, in neutral to alkaline soil. Dig in organic matter (such as well-rotted manure or peat-free compost) to improve water retention and drainage. Protect from slugs.
In fall, cut back any spent flowering stems and fork in organic matter before planting perennial helianthus at the back of a sheltered sunny border.
When to plant Mexican sunflower seeds
The Mexican sunflower (Tithonia rotundifolia) is a gorgeous annual with sumptuous bright-orange flowers on tall stems from mid-summer into late autumn. It attracts butterflies and makes a great cut flower. One of the best varieties to grow is ‘Torch’. Sow it under cover or direct.
Sow under cover
Being a half-hardy annual, tithonia can be sown under cover in early or mid spring to produce flowers earlier.
‘If sowing indoors, we would recommend starting the seeds in March or April,’ says Nina Marshall at Chiltern Seeds. ‘They like a temperature of 55 to 65°F (13 to 18°C) for germination, so you may want to use a propagator or cover the tray to retain warmth and moisture.’
Be patient after sowing, advises Catherine Kaczor of Hudson Valley Seed Co: ‘It is slow to start, so you may see it lagging behind other seedlings, but not to worry. Once tithonia is established, it will take off.’
When the weather has warmed in late spring, Mexican sunflowers can be sown direct into soil outside. ‘We grow them on our trial plot every year and sow direct in the first week of May,’ says Nina Marshall. ‘They always provide us with an abundance of flowers.’
Choose a spot in full sun where tithonia has room to grow (it can reach 6ft (1.8m) or more) and ensure the soil is well drained. ‘Don't worry about fertilizing,’ advises Catherine Kaczor. ‘Too much fertilizer can result in fewer blooms and more foliage. Tithonia is pretty low maintenance and fun to grow. When blooms come in mid to late summer, enjoy watching the parade of pollinators that will follow.’
When to plant sunflowers in pots
Compact annual helianthus can be grown in well-drained pots of compost on a sunny terrace or windowsill. This is a great way for children to get involved in sunflower growing. Try the characterful ‘Short Stuff’ or the shaggy ‘Teddy Bear’, which don’t get too tall.
‘My favorite kid-friendly sunflower is ‘Teddy Bear’,’ says Shannie McCabe, ‘The plants are short, just 18 to 24 inches tall and the heads are unique, having fully double petals that make the flowers very fluffy, just like a teddy bear! It’s quick to mature and easy to grow.’
As for when to plant sunflowers in pots, you can get potted annuals off to an early start. Sow them under cover (for example, in a greenhouse or on a bright windowsill) in March or April in the containers they are going to grow in. Alternatively, sow them outside from mid-April to mid-June into the containers they are going to grow in. Choose a well-drained pot that is large enough to contain the dwarf sunflower once it reaches its full size (usually around 2ft (60cm)). Place the pots in sun, water regularly (especially in hot, dry weather), and look forward to their cheery golden flowers bursting into bloom come summer.
After experience in the fashion industry, Hazel became a beauty and wellbeing journalist, and worked for The Ecologist as Green Living Editor. During a period of injury, she studied horticulture and garden design, and went on to work as a gardener and write about gardening for national newspapers, including The Guardian. Today, she enjoys regularly contributing to print and online magazines, including Amateur Gardening and Homes & Gardens.
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