Pinching Sunflowers

Many sunflower varieties we use for cut flowers produce one flower and no branches.  And since those flowers tend to be larger than most consumers want, we have learned to crowd them in the field to keep them small.  What if we pinch the plants early, forcing them to branch?  Would that increase yield, reduce flower size, and reduce the need to sow as many seeds?  Yes, but it depends.  In 2006, we pinched ‘Procut Orange’ and ‘Sunrich Orange’ sunflowers grown at 9 x 9 in. spacing in a 4-foot bed, and found that while we increased stem yield from 1 to 4 per plant, the flowers were too small to be attractive.  So in 2007 we varied the plant spacing to see if a wider spacing, combined with pinching, would produce good yields of high quality flowers.
    
As in previous years, we compared two varieties: ‘Procut Orange’ and ‘Sunrich Orange.’  Spacing treatments included: 9 x 9 in. with 4 rows per bed, and 12 x 12 in. with 3 rows per bed.  Pinching treatments were an unpinched control and a soft pinch leaving 4 nodes.  Seeds were sown on June 1, and transplanted on June 20.  Plants were pinched on July 2.  Flowers were harvested, and flower diameter measured, when the petals were at right angles to the flower disk.
    
Pinching increased yield of stems from 1 to 3.6 per plant, but delayed flowering by 6 days (Table 1).  Stem length of branches harvested was reduced by nearly 50%, but stems were still of adequate length.  The 39% reduction in flower diameter could constrain sales to some customers, however, especially those at farmers’ markets.  Smaller flowers are more readily accepted by florists because they are easier to work with in small arrangements. By increasing the spacing from 9 x 9 in. to 12 x 12 in., the flower diameter of the pinched plants increased from 2.1 to 2.4 in., perhaps sufficient enough to increase marketability (Table 1).

‘Procut Orange’ flowered 9 days earlier than ‘Sunrich Orange’ in this trial, and was shorter (Table  2).  When pinched, the former produced significantly more basal branches.  This may have been due to a lower incidence of a lower leaf necrosis that severely affected ‘Sunrich Orange’ in this trial (Fig. 1).  Since removal of the stem tip deprived it for a time of new leaves, the state of health of the old leaves could have adversely affected the production of branches.

When yields are calculated on an area basis, assuming that beds are spaced 6 ft apart, pinched ‘Procut Orange’ at the closer spacing is nearly 4 times as productive as either variety that has not been pinched at that spacing (Table 3). 

Pinched ‘Procut Orange’ plants grown at the wider spacing were 28% more productive than pinched ‘Sunrich Orange’ plants at the narrow spacing.  This indicates that choice of variety and spacing can result in considerable increases in sunflower productivity through the use of pinching.

Table 1.  Effect of spacing and pinching of sunflowers on stem yield, earliness of flowering, stem length and size of flower in a field experiment on ‘Procut Orange’ and ‘Sunrich Orange’ sunflower.

TreatmentsStems/plant (No.)Days to first flower from sowingStem length (in.)Flower diameter (in.)
Pinching: None1.064473.6
Pinched3.670262.3
Statistical signficance************
9×9, none1.065483.4
9×9, pinched3.371232.1
12×12, none1.064463.8
12×12, pinched3.869282.4
Interaction significance*ns**ns


Table 2.  The influence of variety and pinching, and their interaction, on yield and components in the sunflower pinching experiment.

TreatmentsStems/plant (No.)Days to first flower from sowingStem length (in.)Flower diameter (in.)
Procut Orange2.663332.8
Sunrich Orange1.972403.1
Statistical significance*****ns
Procut control1.061433.5
Procut pinched4.365232.1
Sunrich control1.068513.7
Sunrich pinched2.875282.4
Interaction significance***nsnsns


Table 3. Stem numbers harvested per 100 ft. of row, for the two sunflower varieties when grown at two spacings in the bed, and either pinched or not pinched.

Variety9×9 inch spacing9×9 inch spacing12×12 inch spacing12×12 inch spacing
 ControlPinchedControlPinched
Procut Orange5332,1334001,840
Sunrich Orange5331,3324001,240

 

Chris Wien is Professor of Horticulture at Cornell University. The excellent assistance of Liza White, supervisor, and assistants Martha Gioumousis, Teddy Bucien and Liz Stuprich is gratefully acknowledged. Many thanks to Johnny’s and SeedSense seed companies for donation of the seeds used in this trial.