Can We Make Sunflowers More Productive with the Right Pinching and Spacing Combinations?

Wouldn’t it be nice to cut more sunflower stems with less work? Yes, you say, but what’s the catch?  It comes down to whether you would rather plant, or pinch. Sunflowers grown as cut flowers can be sorted into two groups: those which have a single stem, and do not branch under normal spacings, and those which develop a smaller central flower, but produce many harvestable branches. The former are preferred by commercial producers, the latter are marketed more to home gardeners. But the branching types form few branches when crowded, and both types will branch if deprived of their growing point (pinched or topped) when they have about 6 fully developed leaves, before flowering. So depending on how you handle them, the two types tend to merge.

We conducted a field experiment at Ithaca, New York (Zone 5), to determine if we could increase sunflower productivity with less effort. The study looked at three varieties, grown at three plant spacings, and either pinched or left alone (single stem). The varieties were ‘Starburst Lemon Éclair’ and ‘Goldrush’, both branching types, and ‘Procut Amber Glow’, a non-branching type. These were grown on 4 foot wide beds, at 6 x 6,
9 x 9 and 12 x 12 in., resulting in 6, 4 and 3 rows per plot, respectively. Half the plots were pinched when the  plants had six leaves  (3 pairs), the rest were allowed to grow normally. We harvested only the inner rows in each plot to avoid edge effects,  and repeated the experiment three times.

The study confirmed the well-known fact that the more stems in a given area, the smaller the flowers. So to evaluate the results of this study, we had to decide what size of sunflower is marketable. We decided that only flowers with a disk diameter greater than 1.5 in. were acceptable, since smaller flowers were frequently misshapen, or had such thin stems that they collapsed.

At the denser spacings, stem numbers and yield increased (Table 1). Pinching also increased stem numbers, about 3 to 4 times, depending on the variety. When the two factors were combined, the number of stems per plot got so high that flower size decreased below marketable levels. The optimum combi-nation of pinching and plant population varied with the variety. For ‘Starburst Lemon Éclair’, all pinching treatments resulted in unacceptably small flowers, although stem yields were high. For yields of nearly 4000 stems per 1000 ft2, the high density unpinched treatment was best. For ‘Goldrush’ and ‘Procut Amber Glow’, pinched plants grown at 9 x 9 in. spacing produced 50% more stems than the unpinched plants grown at 6 x 6 in. spacing, and two and a half times as many as the unpinched plants grown at 9 x 9 in.

What is best in your operation? If planting at high density on your farm is a hassle, consider using a wider spacing and pinching
the plants to achieve good yields. For branching varieties such as ‘Starburst Lemon Éclair’, high density planting without pinching suppresses branching and yields flowers of acceptable size (Fig. 1). Another factor to consider is seed versus labor costs – single stem production requires more seed, but pinching has higher labor costs.  Also, smaller flowers work great for mixed bouquets and arrangements, while larger flowers are usually needed for single species bunch sales at farmers’ markets. If you have a variety of customers, you may want to grow a variety of both pinched and single stem.

Acknowledgements:  I am grateful for the competent technical assistance of Sara Clark and Priscilla Thompson, and thank Dr. Tom Heaton at NuFlowers LLC for supplying seeds and financial support for this study.

Table 1. Effect of spacing and pinching at the 6-leaf stage on yield (stems per 1,000 ft2) and flower diameter of 3 varieties of sunflower grown in a filed experiment in 2011 in Ithaca, New York.

 

Variety Spacing, in.Stem yield/1000ft2Stem yield/1000ft2 Flower diameter, in. Flower diameter, in.  
   Not pinchedPinchedNot pinchedPinched
      
 Starburst Lemon Éclair 6×63,90515,7441.80.9
  9×9 1,7926,9041.91.1
  12×12 9445,1442.21.2
 Goldrush 6×6 4,0839,5001.91.4
  9×9 1,6796,2722.21.6
  12×12 1,1114,2222.31.6
 Procut Amber Glow 6×6 4,00010,9712.11.3
  9×9 1,7295,8762.71.8
  12×12 1,0003,3892.81.8

Chris Wien

Professor

Chris Wien is recently retired Professor of Horticulture at Cornell University. Contact him at [email protected]