Putting plants on hold before shipping
Cold or rainy weather can delay shipping of crops. Review the best strategy to put crops on hold.
Farmers are at the mercy of the weather. That’s especially true for growers of bedding plants since weather not only influences growing conditions, it also influences consumer demand of their products. Greenhouse growers spend a lot of money to mitigate the effects of weather on crop production, which includes the use of expensive structures and energy for heating and lighting. Unfortunately, there’s little growers can do to regulate seasonal demand of spring garden plants. The consumer isn’t inspired to purchase them when it’s cold or rainy, yet many growers have to produce bedding plants for pre-determined dates.
Inevitably, at least once during the feverish spring season, plants are ready for shipping before the market is ready to accept them. This requires growers to hold onto finished plants – often for one or two weeks – before shipping. This can tie up precious production space, but can also lead to “over-ripe” plants that are too large or beyond the desired stage of flowering. What’s a grower to do?
Lower the temperature
According to Michigan State University Extension, this is, by far, the best strategy to hold crops successfully. Temperature is the primary factor that drives plant development, so lowering the temperature slows plant growth. How low can you go? Ideally, plants would be kept just above their base temperatures, which means 45-50 degrees Fahrenheit for cold-tolerant crops, such as alyssum, geranium, marigold, pansy, petunia, snapdragon, etc., and 55-60 F for cold-sensitive crops, such as angelonia, celosia, New Guinea impatiens, pepper, pentas, vinca, etc. At these temperatures, plants should continue to receive at least some light during this holding phase to maintain quality. Visit MSU’s Floriculture website for more information on the base temperatures of bedding plants.
Often times, it’s not easy to hold plants at cool temperatures; space is often limiting and it may already be too warm outside to deliver cool temperatures inside. Growers need to be creative to manage this situation. One strategy is to delay transplant of the next crop so that crops ready for shipping don’t need to be moved. It’s much easier to hold plugs and liners since they occupy less space. If you buy in the transplants, see if they can delay shipping the young plants to you. I’ve also seen growers put finished plants on transport racks and keep them in cool areas until they can be shipped. If kept at low temperatures (40 to 45 F, depending on the crops), plants can tolerate darkness for short periods without negatively influencing quality (see photo).
When necessary, apply a PGR spray
If you anticipate needing to hold crops longer than one week, consider an application of a plant growth retardant (PGR) spray. Sprays are suggested, rather than drenches, because they usually have a shorter period of efficacy. A potential downside though is that late PGR sprays can reduce the size of flowers not yet open. Use rates that are toward the lower end of what you typically use. For further assistance, contact your MSU Extension floriculture educator.
Dr. Runkle’s work is funded in part by MSU’s AgBioResearch.