Here’s a taste of what you’ll find in the book to be published by the ASCFG—Postharvest Handling of Cut Flowers and Greens.

Zinnia

General information: This quintessential garden flower has steadily increased in popularity to become one of the most important field-grown cut flowers. Zinnia violacea (formerly Zinnia elegans) is available in a broad range of colors, lacking only true blue. Bicolors and green zinnias are also available. Be sure to select cut flower types as many compact garden zinnias are available. Zinnia is generally field grown, but can be grown in high tunnels, especially in cool climates.

Stage of harvest: Harvest full flowers as soon as the stem below the flower is rigid to reduce broken head.  

Expected vase life: What is the vase life of zinnia? This should be a simple question, but to quote Janet Foss “Sometimes they last and sometimes they don’t.” Cut zinnias are sensitive to bacterial stem rot, microbial growth in the vase solution, and proper dosing of floral preservatives (see below). While any one of these factors can reduce vase life, commercial holding solutions increase vase life and should be used.  

In North Carolina State University trials, over a dozen zinnia cultivars have been tested, and vase life for most cultivars was 7 to 14 days. A few cultivars such as ‘Zowie! Yellow Flame’ (pictured left) and ‘Uproar Rose’ lasted much longer, up to three weeks. Dozens of cultivars have been evaluated in the ASCFG National Seed Trials, where growers reported an average vase life of 7 to 8 days for most of the varieties, with individual growers reporting anywhere from 3 to 16 days. ‘Zowie! Yellow Flame’ and ‘Uproar Rose’ were reported to last an average of 8.3 and 9.3 days, respectively, with individual growers reporting 6 to 12 days.  

Grower, wholesaler, and retailer treatments: First, make sure buckets are clean, cutters are clean, and fresh solutions are used when handling cut zinnias. Commercial hydrators can be used immediately after harvest for a few hours, but do not leave flowers in too long. Slow release chlorine tablets are particularly effective and stems can stay in the solution for longer. After hydration, place in commercial holding solutions, which will increase vase life by one to five days for most cultivars and should be used. However, zinnias are sensitive to overdosing; do not leave them in flower foods with sugar for more than two or three days.

Storage and shipping procedures: Zinnias should not be stored for more than a week in water, and never stored dry, as they often won’t rehydrate.  There are many reports of zinnias being sensitive to cold storage temperatures. Experimentally, cut zinnias can be held for a short time (1 to 2 days) at 33 to 35F (1 to 2C), but longer storage results in damage, which shows as brown spots on the petals. To be safe, store at 40 to 45F (4 to 7C).  

Ethylene: Ethylene has no effect and 1-MCP and STS use was not beneficial.
 
Foam: Foam will shorten vase life by one to several days

Comments: As if the postharvest challenges were not enough, the neck under the head is hollow and stems should be handled carefully to avoid bent neck. 

For the most complete information on the performance of several zinnia cultivars, and postharvest handling test results, spend some time at North Carolina State University’s Cut Flower Page https://cutflowers.ces.ncsu.edu/cut-flower-cultivar-trials/