Sunflower Plant Profile

closeup of a sunflower

The Spruce / Phoebe Cheong 

Bright yellow sunflowers are the poster flower of summer. Sunflowers are native to North America, but they are very often associated with the Mediterranean area. The flowers have a wide central disk surrounded by shorter petals. The sunflower's sturdy stem can grow 10 feet or more and may hold single flowers or be multi-branched. The seeds are edible and are favored by birds. They are also used to make cooking oil and livestock feed.

Traditionally, sunflowers were a sunny yellow color with a darker central disk. However, now we have a choice of rich chocolate browns, deep burgundy, and luscious multi-colored flowers.

There's a reason they're called sunflowers: The flower heads follow the sun. So give some thought to where you plant your sunflowers. If you plant a row of sunflowers on an east/west axis, you will be looking at the back of the flower heads for most of the day.

Like most annuals, sunflowers are fast-growing plants. They are usually planted from seeds sown directly into the garden in late spring after the soil has warmed to at least 55 degrees Fahrenheit. Most varieties will reach flowering maturity in 80 to 120 days after the seeds germinate.

Botanical Name Helianthus annuus
Common Names Sunflower, common sunflower
Plant Type Annual
Mature Size 3 to 10 feet tall; 18- to 36-inch spread
Sun Exposure Full sun
Soil Type Dry to average-moisture, well-drained soil
Soil pH 6.0 to 7.5 (slightly acidic to slightly alkaline)
Bloom Time Mid-summer to early fall
Flower Color Yellow, red, mahogany, bicolors 
Hardiness Zones 2 to 11 (USDA); grown as an annual
Native Area Plains and meadows of western U.S., Canada, Mexico
group of sunflowers
The Spruce / Phoebe Cheong 
rows of sunflowers
The Spruce / Ana Cadena 

How to Grow Sunflowers

About the only mandatory requirement for growing sunflowers is a sunny location and well-drained soil. If possible, give them a location that is sheltered from winds that might topple these towering plants.

Sunflowers do not like to compete with weeds, so keep the garden clean. Mulching will help with both soil moisture and weed suppression. Gnawing animals are attracted to sunflower seedlings, so some protection when they are young is suggested. Cover them with row covers or screening, removing it when the plants are 1 to 2 feet tall. An easy temporary way to cover sunflowers is to use one of the webbed plastic trays from the garden center. Remember to remove it before the plants grow through it.

Most sunflowers get top-heavy when they bloom and can use the support of staking. If they are planted very close together, sunflowers may support themselves, but usually, heavy rain or strong wind will cause them to lean and they won't straighten up on their own. Planting sunflowers along a fence is the easiest way to stake them. Bamboo stakes are also strong enough to keep them upright. Use care when inserting the stakes, so you don't damage the plant's roots.

Light

For the best flowering and the sturdiest stems, plant your sunflowers in full sun. Since they are heliotropic (their flower heads will turn and follow the sun all day) full sun exposure will help them remain straight rather than bending toward the direction where the light is predominant.

Soil

Sunflowers will grow in almost any soil but will do best in well-drained soil containing a good amount of organic matter.

Water

Although tolerant of dry conditions, watering sunflowers regularly will help them set flowers. They will stop blooming during periods of drought.

Temperature and Humidity

Optimal temperatures for growing sunflowers is 70 to 78 degrees Fahrenheit, but lots of sun is more important than temperature for these plants; they often thrive in the hottest environments and will bloom nicely in areas with chilly but sunny summers. Excessively humid weather can encourage fungal leaf spots and other diseases.

Fertilizer

Sunflowers are extremely fast growers and appreciate a fertilizer high in phosphorus and potassium to remind them they're supposed to set flowers on those tall stalks. Use a slow-release fertilizer, and avoid over-feeding, which can cause the stalks to become spindly.

Growing from Seeds

Sunflowers are usually grown from seed. Seeds can be sown directly into the garden once all danger of frost is past, or they can be started indoors three to four weeks before transplanting. Peat or paper pots are recommended for seedlings started indoors, because sunflowers do not like to have their roots disturbed.

Plant seeds 1 to 2 inches deep in a shallow trench, spaced about 6 inches apart. Cover with soil and keep them watered until they sprout, which takes 7 to 10 days. Taller varieties should be thinned to about 12 to 18 inches apart. Dwarf varieties can be grown about 1 foot apart.

Harvesting Sunflowers

The flowers should begin to mature in early fall. When this happens, the heads will turn downward and the florets in the center disk will shrivel. The only sure way to tell if the seeds are ready to harvest is to pull a few out and open them. If the seed kernels inside the shell are plump, they're ready for harvest. Don't wait too long or squirrels and birds will harvest for you.

To harvest, cut the whole flower head with about 1 foot of stem attached and hang in a warm, dry, ventilated spot, away from insects and rodents. Cover the seed heads with cheesecloth or a paper bag to catch loose seeds. Poke some small holes in the paper bag for ventilation. When the seeds are completely dried and ready for use, they can be easily rubbed off the flower head and collected.

Propagating Sunflowers

Sunflowers can be propagated by taking cuttings and rooting them, but the easier method is simply to collect some of the seeds and save them for replanting the following spring. After harvesting the seeds, carefully select some of the largest, plumpest seeds and store them in a dry, cool location until spring planting time.

If sunflower seed heads are left on the stalks to provide winter food for birds, you can expect them to readily self-seed and send up many volunteer seedings next spring. These volunteers can be thinned out to establish a new patch of sunflowers.

Common Pests/ Diseases

Sunflowers can be affected by a number of animal, insect, and disease issues:

  • Birds, squirrels, and racoons are very fond of the seeds. Use frightening devices or cover the flower heads with netting to protect them.
  • Sunflower moth lays its eggs on the plant and the larvae feed on the flower heads, tunneling and leaving holes in the seed. Pesticides will control the moths.
  • Aphids and whiteflies are common pests. Insecticidal soaps and oils are usually effective at combatting them.
  • Fungal diseases: These include sclerotinia (white mold), downy mildew, and rust. To avoid, provide adequate air circulation or apply a garden fungicide as soon as you spot the first signs of infection.
  • Verticillium wilt: You'll see dead areas in between the leaf veins, with yellowish margins. If this is a problem, choose resistant varieties of sunflowers at next planting time.

The best control of diseases is prevention, by changing where you plant each year and disposing of any infected plants. If you're worried about animals getting the seeds before you, try growing them in a fenced vegetable garden. To further foil squirrels, plant a coarse-leaved vegetable, like squash, at their base.

Varieties of Sunflowers

Wonderful new varieties come out every year. Here are a few standouts:

  • 'Russian Giant' has a single yellow flower that can be as much as 20 inches across. Growing 10 to 12 feet tall, this is a great variety for seed production.
  • 'Teddy Bear' is great dwarf variety with a fluffy flower head, growing 1 to 2 feet tall. It works well in containers.
  • 'Giant Sungold' is a taller version of 'Teddy bear' that grows up to 5 feet tall.
  • 'Autumn Mix' sunflowers are tall growers (6 feet or more) that give you a rainbow of fall colors on large flower heads.
  • 'Italian White' are 4-foot-tall plants with creamy white flowers that produce great seeds for the bird feeder.
  • 'Prado' series are early-blooming, multi-flowered sunflowers in shades of burgundy. These are great flowers for cutting.

Landscape Uses

Be careful when growing the taller varieties of sunflowers, because they can easily shade other plants. Tall sunflowers work best as a screen or in the back of a border. They're also great for growing vines on. Shorter dwarf varieties can be more easily worked into a garden border.

If you are growing sunflowers for cutting, choose a multi-branched variety to get the most blooms. Whichever variety, plant in clusters of at least nine plants for the best impact, and so that they can support each other against wind or rain.

Sunflowers are a good choice if you want to deliberately draw wildlife. Left on the stems, the dried seed heads will lure songbirds to your garden.