Annual sunflowers bloom from summer to autumn. Depending on the variety, they take 11-18 weeks to flower from seed. With that in mind, it’s a good idea to sow sunflower seed every couple of weeks, so you’ll have a constant supply of cheerful blooms throughout summer.
Sunflowers are easy to grow from seed and are ideal for growing with children. They can reach heights of up to 2m, bearing impressive, long-lasting flowers, and look fantastic in gardens and allotments. They also make an excellent cut flower.
Sunflowers are related to Jerusalem artichokes, Helianthus tuberosus. If you plant Jerusalem artichokes and let them flower, they will bear beautiful, sunflower-like blooms.
How to grow sunflowers
Growing sunflowers from seed is easy, you just need a sunny, sheltered spot and good soil – add plenty of well-rotted manure or garden compost before planting to enrich your soil, if you can. Protect the young plants from slugs and snails, and water regularly. You may also need to stake them if they’re in an exposed position.
Choose your variety carefully as dwarf sunflowers grow to just 50cm, while taller varieties can reach up to 3m in height. Sow seeds in pots from April and plant out when all risk of frost has passed. Water frequently and, if growing for height, feed weekly with a nitrogen-rich fertiliser to encourage them to grow tall. You may need to stake some of the taller varieties.Sunflowers need sun. For best results, grow them in a rich, fertile soil in a sheltered, sunny spot.
Sunflowers grow well in pots but if you’re growing for height, it’s best to grow them in the ground.
When to plant sunflower seeds
The best time to plant sunflower seeds is between April and May. Sow seeds individually in 10cm pots of peat-free, multi-purpose compost. Cover the pots with a clear plastic bag and place them in a sunny, warm spot for the best chances of germination. Remove the plastic cover once the seedlings have emerged. When the seedlings are large enough to handle, harden them off gradually – for about two to three weeks – then plant them outdoors. You may need to protect them from slugs and snails.
How to plant sunflowers
If your garden has a lot of slugs and snails, your sunflowers may benefit from being potted on into larger pots of fresh compost, then hardened off before planting out into the soil. This means the plants will be bigger when in their final growing positions, and therefore more resilient to slugs and snails. Regardless of how big they are when you plant them, don’t plant them out until all risk of frost has passed, usually from June onwards.
When planting out, prepare the soil by removing weeds and add plenty of organic matter such as compost or well-rotted manure. Plant the sunflowers at the same depth they were in the pot. Water well and stake taller varieties with a bamboo cane or similar.
Growing sunflowers in pots
Sunflowers do well in pots, although they usually don’t grow as tall as those growing in the ground. Sunflower plants are heavy feeders, so make sure you water the pots regularly (daily in hot weather) and feed fortnightly with a nitrogen-rich fertiliser, switching to a high-potash fertiliser, such as a tomato feed, when the plants begin to bloom.
To grow sunflowers in containers, sow the seeds in small pots as you would normally in spring, and then transplant them individually into larger ones when they’re large enough to handle, eventually potting them on into a 30cm pot of loam-based, peat-free compost, ideally with added organic matter. Stake taller varieties as you would for plants growing in the ground.
Caring for sunflowers
Annual sunflowers need plenty of water and will suffer if allowed to dry out. If you’re growing for height, feed them fortnightly with a nitrogen-rich fertiliser and then switch to a potash-rich tomato feed just before flowering.
Stake tall varieties with a sturdy cane to prevent wind rock, especially if growing in an exposed position.
After flowering, leave the faded flower head intact so the birds can feast on the seeds. Once they have eaten their fill pull out the entire plant and put it on the compost heap.
How to propagate sunflowers
After flowering, sunflower heads develop masses of seed. You can harvest these to use in cooking, but bear in mind you will need to remove the tough seed coat before eating. Better still, remove the seeds from the seedhead and leave them to dry for a few days, before storing in a paper envelope in a dry spot, so you can sow them the following year. Make sure you leave some seeds for the birds, too.