Signs of spring at The Morton Arboretum may be subtle, but they’re here.
Examine a bare-seeming branch from a tree or shrub and you are likely to see a row of pointed or rounded buds. If you’ve been keeping track, you’ll see they are larger than they were a month ago. Inside, tightly packed leaves and flowers are getting ready to burst out of the buds after spending the winter huddled in warm coats, Janoski said.
Those buds developed back in summer or early fall and were wrapped in a sturdy protective casing of closely fitting husks called bud scales.
What tells a plant it's time to open those overwintering buds? It's different for every species, but usually it's a complex interaction between warmer temperatures and shorter nights as the days grow longer.
When the plant gets the right signals, it produces hormones that trigger buds to start growing rapidly. Water rises from the roots to fill all the new cells like water balloons. The pressure forces the bud scales open, and a new leaf or flower that had been packed in like a crinkled-up tissue unfolds into the sunlight.
Among the first buds to open are the flower buds of trees such as maples, elms, and birches. You might notice them as a green glow in the treetops. These trees bloom before their leaves unfold because their flowers are pollinated by the wind. Leaves would get in the way.
Wind-pollinated flowers are subtle because they don’t need to be flashy to capture pollen from the breeze. Big, eye-catching flowers such as those of magnolias and crabapples are advertising, evolved by plants that need insects to carry their pollen from male flower parts to female pollen parts.
Why do some other plants with obvious flowers, such as the witch-hazel, Cornelian-cherry dogwood and Lenten roses (hellebores), bloom so early? Because early in the season they face less competition for insects’ visits. Bumblebees and flies may be few in March, but there are some, and early bloomers get their full attention.
These are just a few of the signs of spring you will notice along an Arboretum trail in March, if you’re paying attention to the trees.