What if You Can't Transplant On Time?

Many important cut flower species are transplanted.  When field weather conditions are awful, should you wait for better weather? If so, for how long? Or should you just pitch the plants? We answered these questions for zinnia ‘Uproar Rose’, lisianthus ‘Echo Champagne’, celosia ‘Spring Green’, larkspur ‘Sublime Dark Blue’, and godetia ‘Flamenco Salmon’.

We conducted trials in 2010 in Ithaca, New York (Zone 5) to determine effects of flat size and delayed planting to the field. Treatments included: (1) Starting the seedlings in a 72-cell tray in a greenhouse, and transplanting to the field when the seedlings could be pulled (seedlings formed a root ball and could be removed from the tray without leaving seedling mix behind); (2) Similar to 1, except that seedlings were started in a 200-cell tray; (3) Seedlings started in a 200-cell tray, but transplanted to the field 2 weeks late; (4) Seedlings started in a 200-cell tray, transplanted 3 weeks late; and (5) Seedlings started in a 200-cell tray, transplanted to a 72-cell tray when treatment 1 went to the field, and not transplanted until week 5. 

Since each species reacted differently to crowding and delayed transplanting, the results will be described for each, starting with the toughest and ending with the most sensitive.

Zinnia ‘Uproar Rose’:  There was no difference in the number of stems per plant over the season among any of the treatments. Seedlings transplanted on time out of large cells formed the largest plants at flowering, but the other treatments caught up. Plants produced 9 marketable stems averaging 20 inches long. The worst treatment was #4, in which the plants had been crowded in small cells for 3 extra weeks, but aside from a 2-week delay in flowering, and a 17% shorter stem length; stem numbers were the same (Fig. 1).

Lisianthus ‘Echo Champagne’:  As in similar experiments run in past years, lisianthus was not seriously affected by seedling crowding and delayed transplanting. Yields ranged from 2 to 5 stems per plant, with seedlings transplanted 3 weeks late out of the 72-cell tray (#5) doing the best, and the 2-week delay treatment (#3) faring the worst. Stem lengths varied only from 14 to 16 inches.

Celosia ‘Spring Green’:  This cockscomb variety is non-branching, producing a single fan-shaped flower when well grown (Fig. 2). All treatments retained perfect stands after transplanting, so yields were judged on the basis of comb size. Paradoxically, although plants at flowering in treatment 1 were nearly 8 times bigger than those transplanted 3 weeks late from 200-cell trays, combs were less than half the size of the latter. Weather conditions after transplanting of the earlier treatment were cold and unfavorable for comb development, whereas the later transplants went into warmer field conditions. The results indicate that this variety of celosia does not react adversely to crowding, but is sensitive to weather conditions at transplanting.

Larkspur ‘Sublime Dark Blue’:  This species was sensitive to poor seedling growth conditions. If delayed in the transplant container, the seedlings became tall and thin, and did not survive the transplant process (Fig. 3). Only 35 and 39% of seedlings held in the 200-cell containers for 2 and 3 weeks, respectively, survived in the field until flowering. Seedlings grown in 72-cell trays and transplanted promptly had high survival rates and produced the largest plants (Fig. 3). Transplanting from small to large cells increased survival, but the plants were too small at transplanting to be productive.

Godetia ‘Flamenco Salmon’:  Conditions in the transplant container are the key determinants of success for this species. Crowding of seedlings in a 200-cell tray made seedlings thin and spindly, and the resulting plants lacked branches and the ability to form many stems (Fig. 4). In addition, these weak, crowded plants had reduced survival at transplanting, similar to larkspur.

Conclusions: These studies demonstrate that easily transplanted species such as zinnia, lisianthus and celosia tolerated crowding in the seedling stage, and delayed transplanting. Larkspur and godetia are sensitive to crowding in the seedling stage, which inhibits their survival and further growth after transplanting.  In the latter species, the negative effects of delayed transplanting were not helped by temporarily transferring plants from small to larger cells. If grown in flats, these species should be grown in large size plugs and transplanted as soon as the root ball can hold together.

Footnote:  Many thanks to the ASCFG Research Foundation for support of this research. I am also grateful for the assistance of Andrew Hoffman and Sarah Smith in conducting this work. For more detailed results of this work, consult my research page in  the website of the Cornell Dept. of Horticulture                             (http://hort.cals.cornell.edu/cals/hort/research/wienresearch.cfm).

Chris Wien

Professor

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