From an astronomical perspective, the first day of spring is the spring equinox, the day when the sun passes directly above the equator, occurring around March 21 each year. From a biological perspective, spring arrives when plants and animals respond to an accumulation of seasonal signals, such as growing warmth or longer days. Plants bud, birds fly north and insects emerge from tree holes and leaf litter. This seasonal timing of plant and animal life stages is called phenology.

For many plants, warming days are one of the main signals that it’s…