Helenium autumnale (common sneezeweed): Before plant breeders got into the act, common sneezeweed was strictly a fall-bloomer, flowering from late summer until frost, giving almost 10 weeks of display. However, most modern hybrids have some genes of orange sneezeweed (H. hoopesii), so that many start blooming in midsummer and hang on until fall. Some start to bloom in early summer and finish before autumn even begins.
Among the hybrid cultivars, 'Bruno', with bronze-red flowers from late summer through fall, is my favorite. 'Butterpat' is an old favorite, with butter yellow flowers on 4 to 5 foot tall plants. 'Moerheim Beauty' has striking brownish red petals.
Soil: Heleniums grow best in moist, even wet, poorly drained soil. They don't need rich soil and, in fact, in soil that is too rich, they produce impossibly tall plants with luscious green leaves and few flowers.
Heleniums also perform better in cool soil than in warm soil. What they really like is to have their roots in cool soil and their leaves in hot, blazing, late-summer sun. How do you give them these conditions? A thick layer of mulch—especially shredded leaves—will keep the roots cool.
Another way to help keep heleniums from stretching too tall is to pinch the stem tips in spring or early summer, when the stems are about 6 to 8 inches tall. This encourages bushiness and better flowering.
After a few seasons, the clumps of helenium become more dense and flowering decreases. To rejuvenate the plants (and get more to plant in new spots or to give to gardening friends), dig up the clumps and divide them every four years. Beware that where heleniums thrive, they spread rapidly and attempt to conquer the garden.
After heleniums finish blooming, cut them back hard to help prevent insects and diseases from getting established. If you do this each season and divide the clumps every four years, your heleniums are likely to remain problem-free.
Plant Profile: Helenium
USDA Plant Hardiness Zones: 3 to 9
Bloom colors: Copper, orange, red, white, or yellow
Bloom time: Late summer to frost
Length of bloom: 6 to 10 weeks
Height: 3 to 5 feet
Spread: 18 to 36 inches
Light preference: Full sun
Soil preference: Moist or even poorly drained; average fertility
Garden uses: Cutting flower; meadow garden; mass planting; back of border