Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
In our region, commercial strawberries are grouped in two classes based on their flowering habit: those that flower and fruit mostly once in the spring and those that continue to flower and fruit as long as temperatures are moderate. Strawberries thrive in cooler weather and production is affected when temperatures are hot.
Short day or June-bearing has been used to describe plants which start to bloom in late winter and produce one fruit crop per spring. Day-neutral, long day, or repeat blooming have all been used to describe plants which flower multiple times and produce multiple crops over the course of the spring, cooler parts of the summer and fall.
Most of our commercial strawberries planted on Delmarva are June-bearing types. They start initiating flower buds after planting in the fall and begin flowering in late winter and spring as temperatures warm up. Flowering will continue until critical high temperatures are reached. This critical temperature at which flowering slows or ceases varies with cultivar but ranges are 80 to 86 °F daytime and 75 to 78 °F nighttime. At these temperatures runners form instead of flower-bearing branch crowns. The 90 °F temperatures we had this past weekend will have effectively stopped flowering in June-bearing varieties. Day-neutral varieties may also have stopped flowering but will start flowering again when temperatures drop down below the critical values noted above. Day-neutral varieties are also induced to produce flowers as days get longer in June.
June-bearing strawberries starting to runner in the heat.