Hydrators, holding solutions, sugar solutions, STS, Ethyl-Bloc, bulb flower food: The list of postharvest products for cut flowers is getting longer every year, as research reveals ever more information about how to make cut flowers last.
For the vast majority of flowers, however, postharvest doesn’t have to be complicated. Cleanliness, good water, and an all-purpose holding solution can provide exceptionally long vase life for most of the flowers you grow. In fact, many flowers will do fine in plain water.
Researchers at North Carolina State University recently tested 50 relatively new cut flower cultivars to find out how to get the best vase life. They got some surprising results, including a number of flowers that held up just as well - or even better - in plain water as in floral preservatives. Many of the flowers, when handled carefully, got two to three weeks of vase life.
Dr. John Dole, who headed that research, still recommends a floral preservative “as a bit of insurance.” But for those who don’t use postharvest products because of organic certification, or for those experiencing vase life problems, there is much to be learned from this research.
Dole’s research team tested each cultivar with four different postharvest treatments:
- hydrator only,
- holding preservative only,
- hydrator followed by holding preservative,
- water only
Hydrators consist of a germicide, a wetting agent and an acidifier to help the stems take up water quickly. Holding solutions are low-sugar preservatives designed to be used by the grower or wholesaler until the flowers are sold. Holding solutions contain less sugar than all-purpose flower food (which was not tested in this study), and is designed for use by the final consumer. The two most widely known holding solutions are Chrysal Professional 2 Processing Solution and Floralife Professional.
The water the researchers used was described as “high-quality” water. For initial testing, they used deionized water, then for more extensive testing added tap water as a control. The tap water did as well as the deionized water, but Dole notes that the tap water in the lab is similar to DI water.
“Water-only treatments may not work as well for those with poor quality water,” he said.
If you aren’t sure about the quality of your water, get it tested. Floralife will do it for free. Fill a clean plastic bottle with tap water and close it tightly. Include your name, address and phone number, and mail the sample to Floralife Inc. Attention: Laboratory, 751 Thunderbolt Drive, Walterboro, SC 29488.
Sunflowers generally do best in water; some aren’t affected by postharvest treatments but others were harmed by them. “ProCut Orange’ lasted only five days when both hydrator and holding preservatives were used, but 12 days in water. A holding preservative increased vase life for ‘Stella Gold’ but only by one day, and it caused petal tip browning in ‘Sunny.’
Surprise! Several of the cultivars in the NCSU research did best when cut and held in plain water. ‘Benary’s Lime Giant’ had a 23.5-day vase life in water. Hydrating and holding solutions decreased vase life; when both were used together, the vase life was only 1.3 days.
‘Sun Cherry’ and ‘Sun Gold’ lasted 11 to 12 days in water. ‘Oklahoma Carmine’ lasted 19 days in water and ‘Oklahoma Yellow’ lasted 22 days. Hydrators increased the two ‘Oklahoma’ cultivars by one to two days.
Other zinnia cultivars were not tested, but these results suggest that growers might want to experiment with plain water or a hydrator - especially if you’ve had problems with your zinnias’ vase life.
"A couple big issues with zinnias are that they tend to be sensitive to too much preservative so cutting into a hydrator followed by placing in a holding preservative often causes problems," Dole said. "Also, zinnias tend to be "dirty" flowers and suffer from microbial blocking - so make sure the buckets are clean. As the buckets are often not quite as clean as they should be, the preservatives provide some protection."
The following cultivars did just as well or better in water than in preservatives. Bear in mind these are new cultivars; the researchers did not test older cultivars of the same plants. These results again suggest you might want to do your own testing on the cultivars you grow. The name of the cultivar is followed by its vase life in water. Except for the dahlias and foxgloves, all had more than a week vase life, so if you’re not growing them now you might want to consider them for next year.
- Achillea ‘Cassis’ - 12 days
- Adenophora ‘Amethyst’ - 11 days
- Agapanthus ‘MidKnight Blue’ - 11 days
- Ammi ‘Casablanca’ - 15 days
- Campanula rapunculus ‘Heavenly Blue’ - 15 days
- Caryopteris ‘First Choice’ - 15 days
- Dahlia ‘Karma Naomi’ and ‘Karma Thalia’ - 5-6 days
- Foxglove ‘Camelot Lavender’ and ‘Camelot Rose’ - 8-9 days
- Eupatorium cannabinum - 20-24 days
- Helena Red Shades - 16 days
- Matricaria ‘Magic Lime Green’ - 20 days
- Scabiosa ‘QIS Deep Red’ - 7 days
The list of flowers that do fine in water, without additional floral chemicals, includes other species tested elsewhere. George Staby of Chain of Life Network offers free access to his database of postharvest recommendations for hundreds of flowers. The box at right lists the flowers that he says should be held in water. However, in most cases Staby recommends adding household bleach to the water, at a rate of a quarter-teaspoon per quart, to kill bacteria.
Finally, research at Kansas State University found that floral preservatives often cause spotting on the foliage of mint family plants. If you grow basil, monarda, mountain mint, sage, or oregano for cutting, the best approach is to test water versus floral preservatives.
The safe strategy
The most important factor affecting vase life is cleanliness. If buckets, clippers and water are all clean, and the flowers can be kept in a cooler, you can probably forgo the floral preservative on the flowers listed above. But Dole says the germicides in holding solutions will prevent contamination if you slip up in the bucket washing.
“Holding preservatives seem to have the greatest effect,” he said. “So anytime cuts are held for more than a couple hours, they should probably be put into a holding preservative. It is best to cut into water and transfer into a holding preservative. Standard floral preservative works on enough species that everyone should at least test them. In some cases, the results will be dramatic, other cases less so.”
Dole also cautions that growers may not be aware of postharvest problems that occur once the flowers leave the farm - but that those problems may hurt the grower’s business in subtle ways.
“I hear many growers say they don't use postharvest products and haven't had any complaints. This could be because they have ‘trained’ their customers to expect a certain vase life, which could be shorter than what is possible. Also, many flowers do just fine in water and those may be the flowers the grower is producing. If the grower tries other species that require postharvest preservatives, they may fail. I think this sometimes leads to the companion statements that I hear such as ‘I tried that flower but it didn't hold up for me’ - when it does hold up for somebody else. Of course, it didn't hold up - it needed an anti-ethylene treatment, a holding preservative, or some other treatment that the other grower was using.
“Just because a grower isn't getting any complaints doesn't mean that there aren't problems or that the flowers are living up to their full potential. I feel every grower should treat the flowers to provide the maximum vase life. We are getting a long vase life on many of these species because we do everything ‘according to the book.’ The typical commercial flower will have to not only survive the grower handling, but also handling by the consumer which is rarely as good as it should be. The better the flower is treated by the grower, the more durable -- we hope -- it will be for the final consumer.”
For more on postharvest handling of cut flowers, read the article Cater to the special needs of flowers at harvest.