Light is on the way: That’s the message of the celebrations we hold in the dark of winter. Plants already know. Whether it’s a bare elm or oak standing gray and stark against the sky, a pine or fir still cloaked in green or merely a skein of roots curled in the soil beneath a blanket of snow or fallen leaves, every plant is preparing for spring. “The signs are there, even if they’re hard to see,” said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. “Our trees and other plants have been living through cold winters for millions of years, and they have developed a lot of ways to handle it.” Leaves and flowers are so last year. Since they fell to the ground in autumn, they have already begun to decay and become part of the soil. Meanwhile, most trees and shrubs already have buds for the new year’s blooms and leaves. As the days grow longer and springtime approaches, those buds will begin to swell. Beneath the soil, the daffodil and tulip bulbs planted in fall already contain leaves and flowers, packaged neatly with a food supply, waiting for their cue to unfurl. Perennial plants abandoned their stems and leaves and retreated to their roots last autumn so they could shelter from winter’s blasts beneath the soil. Like bare trees, they’re dormant, snoozing, waiting for the biological alarm clock to go off. Other plants simply turn things over to a new generation, waiting out the winter safely inside a seed. Evergreens are slightly less sleepy. They’ve slowed down, but they’re not entirely dormant. Their leaves — often thin and needle-like, to present as little surface area as possible to the drying winter wind — are still green, full of chlorophyll. “On a day that’s not too cold, they may even undertake a little photosynthesis,” Yiesla said, turning energy from thin winter sunlight into food. These plants’ midwinter green is what has made them sacred to many cultures as a symbol of fertility, a reminder that even in cold, dark times, life goes on and spring will come. The signal that means spring is different for every kind of plant and is usually a combination of factors. One is the lengthening of days (or, actually, the shortening of nights), which ticks reliably as a clock. Another is the warming of the soil, which is far more variable and less reliable. Longer days generally mean more sunlight to warm the soil. Ideally, the soil would warm up just enough to signal plants to sprout at the perfect moment, when the danger of frost is past and the days are long enough to give them the energy they need to grow. Chicago weather laughs at such notions. It can bring a frost in May or a 65-degree day in January, far too early for most plants to safely sprout. Plants whose roots are safe under an insulating layer of mulch, the puffer coat of the garden, are less likely to be tricked into sprouting too soon. Some kinds of plants, such as most fruit trees, spring bulbs and native perennials, actually need the cold. They have a chilling requirement, a certain period of time that their roots or seeds must spend in cold soil before they know it’s spring. “They’re counting down the cold days,” Yiesla said. “If the winter is too warm, they may not meet the requirement.” It’s hard to grasp this after a bitter cold spell, but warm winters are becoming more common. Chicago weather is getting more volatile as the global climate changes. Even native plants may not be ready for what it brings every year. Still, most plants will cope. “They’ve had a long time to figure it out and develop a margin for error,” she said. “Every year, the plants that can handle it will. We just have to have faith.” For tree and plant advice, see the online resources of The Morton Arboretum at mortonarb.org/plant-care, or submit your questions online at mortonarb.org/plant-clinic or by email to [email protected]. Beth Botts is a staff writer at the Arboretum. ...read more read less