Bright yellow sunflowers (Helianthus annuus) are the poster flower of summer. They typically begin blooming in the mid-summer and can persist into early fall. The flowers, which stretch around 3 to 6 inches across on average, have a wide central disk surrounded by short petals. The main species plant features orange-yellow petals with a brown or purple disk, but growers now have produced flowers in several other colors. Sunflowers grow on a hairy, sturdy, upright stem that can be several feet high. The stems can hold a single flower or be branched with multiple flowers. Rough, hairy, oval to triangular leaves grow along the stem. In the fall, the disks give way to sunflower seeds, which are a major draw for birds and other wildlife.
Sunflowers get their common name because the flower heads turn toward the path of the sun each day. These flowers are annuals, meaning they complete their growth cycle in one year. Thus, they are fast-growing plants and typically will reach their flowering maturity around 80 to 120 days after the seeds germinate. They should be planted in the spring after the garden soil has warmed to at least 55 degrees Fahrenheit.
|Botanical Name||Helianthus annuus|
|Common Names||Sunflower, common sunflower|
|Mature Size||3–10 ft. tall, 1.5–3 ft. wide|
|Soil pH||Acidic, neutral, alkaline|
|Bloom Time||Summer, fall|
|Flower Color||Yellow, red, mahogany, bicolors|
|Hardiness Zones||2–11 (USDA)|
|Native Area||North America|
About the only mandatory requirements for growing sunflowers are a sunny location and well-drained soil. If possible, select a location that is sheltered from strong winds that might topple these towering plants. It can be helpful to plant sunflowers in groups, so they can support each other against wind and rain. Growers often have to stake their sunflowers, especially the tall varieties, to keep them growing upright. The plants can get very top-heavy when in bloom. 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.
Sunflowers don't like to compete with weeds, so keep the garden clean. Mulching around your sunflowers will help with both maintaining soil moisture and weed suppression. Furthermore, wildlife is often attracted to sunflower seedlings. So it's best to protect seedlings with row covers or screening, removing the cover once the plants are 1 to 2 feet tall.
For the best flowering and sturdiest stems, plant your sunflowers in full sun, meaning at least six hours of direct sunlight on most days. Because they are heliotropic (their flower heads follow the sun), ample sun exposure will help them remain straight rather than bending toward the direction where the light is predominant.
Sunflowers will grow in almost any soil. They can tolerate poor, dry soils. However, they will do best in well-drained soil that contains a good amount of organic matter.
Although tolerant of dry conditions, watering sunflowers regularly will help them set flowers. They often stop blooming during periods of drought. Allow the top 1 to 2 inches of soil to dry out between waterings. If your sunflowers are drooping and the soil is dry, that’s often a sign they need more water.
Temperature and Humidity
Optimal temperatures for growing sunflowers are between 70 and 78 degrees Fahrenheit. But they are tolerant to high heat as long as their moisture needs are met. And they can handle somewhat chilly but sunny environments. Plus, they’re tolerant to high humidity, but they must have well-draining soil and good air circulation to prevent root rot and other disease.
Sunflowers appreciate a fertilizer high in phosphorus and potassium to remind them that they're supposed to set flowers on those tall stalks. If you have a rich, loamy soil, you might not need to supplement with fertilizer. But if you have poor soil, apply a slow-release fertilizer starting in the spring, following label instructions. Be careful not to overfeed your plants, which can cause the stalks to become spindly.
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 planting the following spring. The flowers should begin to mature in the 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 whether 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 harvesting.
To harvest, cut the whole flower head with about 1 foot of stem attached, and hang it 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 small holes in the cover for ventilation. When the seeds are completely dry, they can be easily rubbed off the flower head and collected. Select some of the largest, plumpest seeds that will have the best chance at germinating, 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 the next spring. These seedlings can be thinned out as needed to establish a new patch of sunflowers.
How to Grow Sunflowers From Seed
Sunflowers are usually grown from seed. Seeds can be sown directly into the garden once the threat of frost has passed in the spring, or they can be started indoors three to four weeks before transplanting into the garden. Peat or paper pots that ultimately can be planted directly into the ground are recommended for seedlings started indoors, as sunflowers don't like to have their roots disturbed.
Plant seeds in the garden 1 to 2 inches deep in a shallow trench spaced about 6 inches apart. Keep them lightly moist (but not soggy) until they sprout, which takes around seven to 10 days. Taller varieties should be thinned to about 1 to 1.5 feet apart. Dwarf varieties can be grown about a foot apart.
Several pest and disease issues can affect sunflowers. Birds and rodents are very fond of the seeds. So if you'd like to save seeds for planting, cover the flower heads with netting to protect them from the pests. Moreover, the sunflower moth lays its eggs on the plant, and the larvae feed on the flower heads, tunneling and leaving holes in the seeds. Pesticides can help to control the moths. Similarly, you might have issues with beetles or caterpillars eating foliage. Sunflowers also can be prone to fungal diseases, including powdery mildew and rust. To avoid such diseases, provide adequate air circulation around your plants, and apply a garden fungicide as soon as you spot the first signs of infection.
- '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 a 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' sunflowers are 4-foot-tall plants with creamy white flowers that produce great seeds for the bird feeder.