Allen Wilson


Question: In various articles you have described plants as long-day, short-day and day-neutral. Was that a reference to the number of hours of sunlight? How do plants respond to changes in day length?

Answer: Yes, day length or photoperiod is a major factor used by plants for various processes. Plants use day length to tell them when it is time to go dormant in the fall and when to wake up from dormancy in the spring. Most of us assume it is the change in temperature that induces dormancy. But changing temperature is variable and is not always accurate enough to protect plants from sudden temperature drops in the fall. Likewise, an unusually warm late winter spell could stimulate new growth that would be damaged by a return to normal cold. I noticed that trees growing here started losing leaves at about the same time as the same tree species in a colder winter climate.

Allen Wilson can be contacted at

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