How to grow Helianthus (sunflowers)

What are sunflowers?

Most of us are familiar with the traditional tall sunflower with its large yellow daisy-like bloom, but there’s far more to sunflowers than that. They come in various forms, both short-lived annuals and longer-lived clump-forming perennials.

The annual types include the show-stopping giants topped with dinner-plate-sized, golden flowers, but there are also many other choices, of various heights, both single-stemmed and branching. The flowers come in all sizes and in colours from sunny yellow to cream, orange, ruby and chocolate brown. 

There are also several hardy perennial sunflowers (which come back each year). These produce lots of small to medium-sized sunny flowers on tall stems from midsummer into autumn. 

Annual sunflowers are a popular choice for introducing children to growing plants from seed, as they germinate easily and quickly, and produce such spectacular results. In fact they’re fun for all ages to grow, including adults!

Sunflowers are also great for wildlife. The flowers attract bees and other pollinating insects, while the abundant seeds are a valuable high-energy food for seed-eating birds, such as finches, and small mammals. Many sunflowers have the RHS Plants for Pollinators award, so look out for the logo on seed packets.

Sunflowers make long-lasting cut flowers too. The smaller-flowered types, with their abundant blooms over many months, are particularly popular with flower arrangers. The more unusual colours, including chocolate brown, cream and dark red, are particularly sought-after.

How to choose sunflowers

Annual sunflowers

• These are the most popular type of sunflower – being annuals they last just one year, but are very easy to grow from seed each spring (see Propagating, below). 

• There are many different types, from the familiar towering giants topped with a large sunny flower, to more compact plants with many smaller blooms. They can range from a mere 30cm (1ft) tall up to 3m (10ft) or more.

• The flowers vary in size too, from huge dinner plates to small teacups, and not just traditional yellow, but various shades of cream, red, orange and brown too.

• If you want to grow super-tall sunflowers, you need to choose the right cultivar. Some have been bred to grow particularly tall, while others will never reach lofty heights however well you look after them. The cultivar names are often a giveaway – good choices include ‘Giraffe’,  ‘Russian Giant’ and ‘Titan’. Seed packets or online descriptions will also give you the height.

• At the other extreme, there are dwarf sunflowers that reach just 30cm (1ft) tall. These produce a multitude of small sunny flowers and are ideal for growing in containers or at the front of borders. Look for names such as ‘Munchkin’ or ‘Little Dorrit’.

• In between the giants and the dwarf types there are lots of medium to tall cultivars, in various fiery shades, so browse the seed packets in garden centres or online seed stockists, and take your pick!

• These vigorous, easy-to-grow plants bloom abundantly throughout late summer and into autumn.

• As they are perennials, they die down into the ground over winter and re-sprout from the base in spring.

• Most form large clumps, easily 1.5m (5ft) wide and 2m (6½ft) or more tall, so are ideal for the back of borders and large prairie-style plantings.

• ​They combine well with tall ornamental grasses and other late-flowering perennials. 

• Jerusalem artichokes are also a type of perennial helianthus (Helianthus tuberosus), and although grown for their edible tubers, they do also produce small sunny flowers on tall stems in late summer. 

Buying sunflowers 

RHS guide to choosing healthy plants

RHS guide to choosing healthy plants

Where to plant sunflowers

As their name suggests, sunflowers love a sunny spot. To fuel their vigorous growth, they also like rich soil with plenty of added organic matter, such as garden compost. Dig this into the whole planting area, rather than just into the planting hole, especially when planting long-lived perennial types, to encourage their roots to spread out.

Annual sunflowers

• Medium to tall sunflowers are best planted in a sheltered location, out of strong winds, to keep them upright. Even then, they should be supported with sturdy cane as they tend to become top-heavy so are very easily toppled 

• Giant sunflowers that will reach over 2.4m (8ft) tall are best planted next to the house, so they can be attached to the wall for support. Bamboo canes won’t usually be long or strong enough to support them

• Dwarf sunflowers (30–60cm/1–2ft tall) don’t usually need support and can be grown at the front of borders or in containers

• ​Plant in quantity for bold impact, woven through borders or in large groups

• When growing for cut flowers, you may prefer to plant them in a separate cut-flower bed or on a veg plot

Perennial sunflowers

• Plant these towards the back of borders, where they’ll add valuable height (2m/6½ft or more) and late-summer colour

• Give them plenty of space, as they can form substantial clumps at least 1.5m (5ft) wide

• Some species, such as Helianthus pauciflorus and H. salicifolius, prefer dry soil, while H. × laetiflorus and H. multiflorus thrive in moist or damp soil and like growing near water

• ​They combine well with tall grasses and other late-flowering perennials

When to plant sunflowers

Annual sunflowers are usually grown from seed, sown indoors in spring (see Propagating, below). Keep them on a sunny windowsill or in a greenhouse until late spring or early summer, then plant outside once the soil is warming up and there is no risk of frost. Harden them off thoroughly first, to acclimatise them to outdoor conditions. 

Perennial sunflowers are best planted in spring or autumn, when the soil is warm and damp. They can also be planted in summer if bought in flower, although they will need regular watering to help them get established successfully.
 

How to plant sunflowers

Sunflowers, both annual and perennial, are easy to plant – see our guides below for full details. Water both types thoroughly to help them settle in, and continue watering regularly throughout the summer.

It is also worth noting that slugs and snails love to feast on young annual sunflowers. So wait until your seedlings are strong and resilient, and harden them off well to toughen them up before planting out, so they are less vulnerable. Also see our guide to deterring slugs and snails.

Watering and mulching

• Annual sunflowers need regular and generous watering. The taller types, in particular, mustn’t be allowed to dry out, as they will struggle to recover. One of the secrets to growing giant sunflowers is to keep them consistently well watered

• Plants in containers are always more prone to drying out, as there is relatively little compost. So if you’re growing dwarf types in patio containers, water them whenever the compost feels dry – even daily in hot weather

• Perennial sunflowers need to be watered for the first year after planting, but after that these robust plants should only need additional water during periods of drought  

• Mulching helps to hold moisture in the soil – apply a thick layer of mulch, such as garden compost, to the soil around your sunflowers after planting. Leave a gap around the base of the stems though, to prevent rotting. Perennial sunflowers should then be mulched every spring and/or autumn

Feeding

• Annual sunflowers, whether growing in the ground or in containers, benefit from regular feeding with potassium-rich tomato fertiliser to encourage flowering. Always follow the dosage instructions on the pack 

• Perennial sunflowers don’t generally need feeding, although you could apply a general fertiliser in spring to boost growth

Staking plants

Most annual sunflowers need support, as their large or abundant flowers often make them top-heavy:

• Put a strong bamboo cane in place at planting time, tall enough for the plant’s eventual height (check seed packets for details)

• Loosely tie the stem to the cane, and keep doing this further up the stem as the plant grows

When growing giant sunflowers that will reach over 2.4m (8ft) tall, it is best to plant them next to the house so they can be secured to the wall. Bamboo canes won’t generally be tall enough or robust enough to hold these giants upright.

Looking after older plants

Annual sunflowers are short-lived plants and naturally die off in autumn, but if you collect some of the seeds you can easily grow new plants the following spring – see Propagating, below.

Perennial sunflowers, on the other hand, live for many years. These vigorous plants will eventually form sizeable clumps. These should be dug up and divided every three to four years to keep them flowering and growing strongly.
 

Annual sunflowers naturally die off in autumn, but don’t cut them down straight away. Leave the plants in place so that birds can feed on all the seeds. Chaffinches, greenfinches and goldfinches love sunflower seeds and are able to hang upside-down on the seedheads while they feed, making them enjoyable to watch. Just make sure you keep a few of the seeds to sow next spring (see Propagating, below).

You can cut down perennial sunflowers to the base when they die back in late autumn, as they don’t produce many seeds. Alternatively, you can leave the stems in place over winter to provide valuable shelter for insects and other small creatures. Just remember to prune them out at the base before new shoots start to sprout in mid-spring, to avoid damaging the fresh growth.

Annual sunflowers

Perennial sunflowers

These are easy to propagate by digging up established clumps in spring or autumn and dividing into several smaller sections, about 15cm (6in) across. These can then be replanted in different locations in the border and should settle in quickly. Water them regularly for their first year.

Sunflowers are generally vigorous, healthy plants, however:

• Young sunflowers are particularly vulnerable to slugs and snails, so either sow the seeds indoors and wait until the plants are tough and less palatable before planting out, or put protection in place 

• With their tall stems and large blooms, annual sunflowers are vulnerable to being blown over. So plant them in a sheltered spot and give them a sturdy cane for support, tying the stem loosely to it regularly as it grows. Giant sunflowers are best grown next to a house wall, and tied to this, as canes won’t usually be tall or strong enough to support them

• Fungal diseases may affect sunflowers in wet summers, including powdery mildew and sclerotinia

Sunflowers can have very rough, hairy leaves and stems, which can aggravate skin allergies, so it is best to wear gardening gloves when handling them.

If you’re a member of the RHS, you can use our online Gardening Advice Service, via MyRHS, for any gardening questions.