Buds in Winter

The miraculous ability of leaf and flower buds on trees and shrubs to survive the deep cold and howling winds of our harsh northern winters amazes me. Because we have a few peach trees, I know that blossom buds can die, usually because of extreme temperature fluctuations in early spring. Once the hard, protective covering, what botanists call the “bud scale,” breaks open, a sudden plunge in temperature can kill the flower bud.

Like seeds, buds are dormant embryos packed into a protective outer scale. The period of winter dormancy lasts several months, and most native N.H. plants will not break dormancy during a fleeting January thaw, a clever survival trick. Tree seeds need the same dormant time period that prevents them from sprouting too early.

When present in high-enough concentrations, a hormone called abscisic acid, found in both seeds and buds, switches off all metabolic activity in the bud. In spring this hormone becomes increasingly dilute, losing its inhibitor capacity, so the buds and seeds burst open.

Buds form during late summer at the base of the leaf stem, unnoticed until the leaves fall. Inside the bud is miniature leaf or flower, ready to explode the following spring.


Here in the north, with short growing seasons, this “head start” system enables woody plants to grow rapidly in the spring and to complete their annual growth cycle before the next winter.

To discover more about this phenomenon, I checked out a few buds on my plants around my home. I marveled at how different they all are. There’s a unique bud design for each species. I picked a few shrub twigs for closer inspection: a fat rhododendron flower bud, a slender and delicate blueberry twig, a sturdy lilac twig. Some different tree species also caught my eye for the striking appearance of their buds: birch, beech, sasafrass, hickory, dogwood, and some peach buds.

The huge rhododendron flower buds are at least twice the size of the plant’s leaf buds and easy to distinguish. I found few, indicating that I won’t have many blooms next summer. I sacrificed one flower to science and cut it open to see what was inside. I cut the bud in half crosswise and inspected it with my 16x loupe. (This is the small, inexpensive magnifying glass that field scientists hang on a cord around their necks and hold close to their eye in bright sun for fantastic magnification).

I saw pale greens and cream shades, outer scales surrounding folded and curled-up flower petals. What a beautiful kaleidoscope design! This fat bud had air pockets between the many layers of embryonic flower tissue—a  layering system providing protective insulation. Skiers and winter hikers keep warm the same way by dressing in many layers to trap air.

I also noticed the big, fuzzy buds of the hardy star magnolia that look like pussy willow blossoms. Another winterizing strategy! The fuzz traps air that helps insulate the flower buds from the cold. Happily, the magnolia is loaded with flower buds I hope will erupt in a stunning display next April.

I studied a few unusual tree buds, including the sharp-pointed beech tree bud that resembles a needle. Birch trees also have similar, but smaller, pointed buds located on opposite sides of delicate, slender, zigzaggy twigs making a graceful line against the snow.

Depending on the type of plant, flower buds may be separate from leaf buds and open at a different time, or the flower and leaves may be combined in a single bud and open together. The distinctive “button” flower bud of my dogwood trees is quite different from the leaf buds. I see that I will have a beautiful display of dogwood blossoms in the spring.

It’s easy to identify buds in your own yard when you know the kind of plant you are looking at. But amazingly, experts can identify trees and shrubs in winter without the leaves. Clues from the buds, leaf scar, twigs and bark, as well as the overall form and structure of the plant help provide the answer.
 
Buds may grow directly opposite each other on the twigs, or they may alternate from one side to another. Many shrubs have opposite bud placement, but only a few trees do. You can easily remember them by the acronym MAD Horse: maple, ash, dogwood and horse chestnut. A tree’s branching pattern, easy to see in winter, is the same as that of the buds: opposite or alternate.

The buds themselves provide many more identification clues: they differ in shape, size, texture, color, and even the way the bud scales are wrapped around the bud. Some buds are so small they are hardly visible and are actually imbedded in the twig.

Next time you venture into the winter woods, take time to inspect one of nature’s subtle miracles, and the winter landscape will come alive.

By Anne Krantz, UNH Cooperative Extension Community Tree Steward and Master Gardene