The genus Helianthus includes the much loved annual sunflower, Helianthus annuus, as well as several perennial species that make great, long-blooming garden plants. These are late season flowers, blooming at the end of summer and into the fall. The daisy-like perennial flowers are smaller than their annual cousins, but they are profuse and long-lasting.
Sunflowers are very tough plants, with native species found everywhere from bogs to prairies.
Appearance: The dark green leaves can be heart-shaped or narrow and lance-shaped. The plants are multi-branched and tend to clump, although some varieties can travel by running rhizomes. Daisy-like yellow and gold flowers with center disks will vary slightly from species to species. There are single and double flowering varieties.
Hardiness Zone: Most varieties are labeled as hardy from USDA Hardiness Zones 4 to 8, but many can stretch to zones 3 and 9, although they may not always have a long enough season to bloom, in zones 3 to 4.
Sun Exposure: Perennial Helianthus will bloom best in full sun, although they can handle partial shade. Without at least 5 hours of sun per day, the plants will have a tendency to get leggy and flop.
Mature Size: Height varies greatly by species and by growing conditions. There are Helianthus that reach only two to three feet tall and others that top ten feet. Most are clump-forming, spreading about three to four feet wide. However, some will spread by rhizomes and can become aggressive in the garden.
Bloom Period: These are late season flowers, coming into bloom toward the end of summer and repeat blooming through the fall. You can easily get 8 to 12 weeks of flowers, from your plants.
Suggested Varieties for Your Garden
Some of the most popular perennial sunflowers are cultivars of Helianthus x multiflorus (many-flowered sunflower), which is a cross between the annual sunflower and thin-leaved sunflower (Heliantus decapetalus).
Most Popular Varieties
- Capenoch Star reaches four feet tall, with bright yellow petals and centers.
- Loddon Gold has puffy, double, golden blooms on six-foot stems.
Varieties That Can Reach Ten Feet Tall
Huge sunflowers are gorgeous and eye-catching. It's important to know, though, that taller varieties do not have similarly large flowers. Even when stalks reach ten feet in height, the flowers remain three to four inches across.
- Helianthus salicifolius (Willowleaf sunflower)is tall and low maintenance, but a traveler. 'First Light' is a popular, shorter cultivar.
- Helianthus maximiliani (Maximilian's sunflower) grows well from seed and will self-sow.
Varieties for Poor Soil
- Helianthus angustifolius (Swamp sunflower) is prettier than it sounds. As a six-foot-tall plant, it is tolerant of salt and poor growing conditions. Its flowers are three inches across, with a reddish center disk.
- Helianthus debilis (Beach sunflower) is frost tender, but very salt tolerant. It grows about four feet tall and spreads somewhat aggressively, with three inch wide pale yellow blooms with purple centers. (Zones 8 to 11.)
Since perennial sunflowers don't bloom until the end of the season, they are best in the back of the border. Luckily their foliage is an attractive dark green and makes a nice foil for summer-blooming flowers. When in bloom, they pair well with most of the late season flowers, as well as with late season, red-tinged grasses like feather reed grass and purple muhly grass. Delicate foliage and flowers like goldenrod and asters and purple flowered fall plants like coneflowers and Joe Pye Weed also make nice partners. Perennial sunflowers make good cut flowers and attract bees and butterflies.
Soil: Helianthus is very tolerant of most soil types and a range of soil pH. They need a fairly rich soil with lots of organic matter. Although they need well-drained soil, they do not tolerate drought well, so keep them watered.
Planting: It is difficult to find the seed of perennial sunflowers because most of the commonly grown varieties are hybrids. But since they are fast growers, the easiest way to propagate them is to divide existing plants every two to three years. You can plant Helianthus in the spring or fall, but a spring planting will reward you with blooms at the end of the season.
Helianthus will spread out by rhizomes. Space your plants at least two to three feet apart, so they have space to grow.
Maintenance: Helianthus are relatively low maintenance. They need to be cut back in the spring, and taller varieties will need staking, or they will fall over. The plants need regular water, to reach their mature height and set blooms. If you do not have sufficient organic matter in your soil, you will need to feed them with a balanced fertilizer in the spring and perhaps again in mid-summer.
Pests and Problems
For the most part, perennial sunflowers are pest-free. They can be prone to powdery mildew, but giving them plenty of air circulation will cut down on that. Keeping the clumps divided every couple of years will also aid in air flow around the stems.