Pinching Lisianthus

The positive yield results obtained by pinching out the main growing point of snapdragons and sunflowers encouraged us to try this technique with lisianthus. In three years of trials, we have obtained a slight increase in number of usable stems in only two instances, and no increase in another. This article summarizes the findings of our 2006 and 2007 trials.
    
Our standard method of growing lisianthus in the field and the high tunnel is to transplant into beds about 4 ft. wide, with 4 rows of plants spaced 9 in. apart in both directions. The beds are covered with black plastic mulch, and irrigated with 2 trickle irrigation lines under the plastic. The variety ‘ABC 2-3 Blue’ (PanAmerican Seeds) was used in both years, along with ‘Cinderella Ivory’ (Johnny’s Seeds) in 2006, or ‘Echo Champagne’ (Johnny’s) in 2007. We grew our own seedlings in 2006, but ordered plugs from Gro-n-Sell in 2007. The 2006 trial was done only in the field; the 2007 experiments were conducted in both tunnel and field. Pinching treatments consisted of removing the plant’s growing point, leaving either 3 or 6 nodes. Ideally, this should be done as soon as the stem has elongated enough to allow removal of the soft growth above the leaves that will remain. We managed to do that in 2006 and in the tunnel experiment of 2007, but did not do the node 3 pinch until 6 nodes had developed in the field experiment of 2007. The sowing, transplanting and pinching dates are given in Table 1.
    
We harvest lisianthus that has not been pinched when one or two flowers have opened on the plant. The person harvesting generally leaves several basal nodes at that harvest, but removes the main stem and all attached branches above that point. As a consequence, there is a pause of several weeks before that plant will produce additional usable stems (Fig. 1). The growing season may not be long enough outdoors for a second flush of flowers, but in Ithaca’s Zone 5, we rely on the season extension of the high tunnel to ensure that the basal branches can be harvested. By pinching out the main growing point, those basal branches are stimulated to grow at an earlier time, and the plant produces several stems at once. The harvest of the pinched plants was delayed about a week compared to the unpinched plants (Table 2). Pinching increased stem length when only the lowest branches were allowed to grow.
    
The effect of pinching on yield of cut stems has varied from trial to trial. In 2005, pinched plants yielded 15 % more stems than unpinched controls. In 2006, there was no yield difference with any pinching treatment. In 2007, pinching at node 6 increased yield by an average of 42% (Table 2). Pinching at node 3 had no effect on yield in the tunnel, but in the field, where that treatment was done relatively late, yield declined with pinching, and delayed first harvest by 19 days.
    
So should you pinch lisianthus or not? Our results indicate that a soft pinch leaving about 6 nodes can modestly increase yields in some seasons. If too few nodes are left, especially when the pinch is delayed, the plant is set back severely. A compromise might be to let some plants produce the earlier flowers without pinching, and pinch others to obtain a possible yield increase.

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 PanAmerican seed companies for donation of the seeds used in this trial.

Chris Wien

Professor

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