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Sunflowers

Pollen-less sunflower hybrid 'Arbel'.

Pollen-less sunflower hybrid ‘Arbel’.

Helianthus annuus

Propagation:

  • Since sunflowers can be easily grown outside, high tunnel production of the crop only makes sense early in the season, before field production is possible.
  • Early sunflowers should be transplanted from greenhouse-started seedling trays.
  • Given the large size of sunflower seeds, 72- to 144-cell trays are best for seedling production.
  • In moderate greenhouse temperatures (65-75 F), expect to transplant in less than 3 weeks.
  • Delayed transplanting of the fast-growing seedlings will result in tall, weak plants that may have impaired growth after transplanting.
  • Direct seeding in late summer for a fall crop may take advantage of frost protection afforded by the high tunnel.
The apical growing point of the lower sunflower has been removed (topped or pinched) to increase the number of flowers.

The apical growing point of the lower sunflower has been removed (topped or pinched) to increase the number of flowers.

Growing:

  • The modern pollen-less hybrids have growth duration from sowing to harvest of between 55 to 75 days when started in early spring.
  • Flower stalk and head size are directly dependent on spacing; for head diameter of 4 to 5 in., plant seedlings 6 x 6 in. in a 4-foot bed, or use a 9 x 9 in. spacing, with two seedlings per hill.
  • Pinching out the plant tip after 4 leaves have expanded will double or triple flower number per plant, but these will be small, unless spacing is widened to 12 x 12 in.
  • For early high tunnel planting in milder zones (Zones 6 and 7), the short daylength in mid-March will cause early flowering of some varieties such as ‘Sunrich Orange’. These plants will flower early on small stalks, and will show excessive numbers of secondary buds.
  • View .pdf of sunflower variety sensitivity to day length.
'Moulin Rouge', a tall, late, branching sunflower variety.

‘Moulin Rouge’, a tall, late, branching sunflower variety.

Varieties:

  • For use as cut flowers, choose varieties that do not produce pollen. These do not stain their surroundings when placed in a vase in the home.
  • There is now a large range of flower colors, sizes, degree of branching, earliness available with pollen-less characteristics.
  • The most common sunflower colors are orange petals surrounding a dark brown disk, but disk color can also vary to green and gold.
  • Varieties that produce only a single stem usually flower over a short period of time, after which the tunnel space can be used for other crops. Branching types can be harvested for several weeks as branches come into flower.

Postharvest Handling:

  • Sunflowers are generally harvested as cut flowers when the flower is just opening, and the ray flowers are perpendicular to the flower disk.
  • The flowers should last at least a week in water at room temperature.
  • There are big varietal differences in flower life after harvesting, and these relate to flower color. The standard orange types tend to be long-lived. Varieties with dark flower color, or with dark petal bases tend to shed petals in less than a week.
  • Short vase life is also related to premature petal loss when flowers are roughly handled at harvest.
  • Harvesting flowers during middle of the day may lead to flower wilting. These should be recut when flowers have been moved to a shaded environment.

For more information, see:

  • Flower seed catalogs
  • Armitage, A.M. and J.M. Laushman. 2003. Specialty Cut Flowers, 2nd Edition. Timber Press, 586 pp. Available through ASCFG
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