November 21, 2010

The science of dormancy

It happened one day last week…I could feel the snow approaching. Anyone who lives or has lived in a northern climate knows what I’m talking about. It’s hard to describe without too much detail, but the feeling made me want to curl up in a warm blanket and hibernate for a few months.

The plants are doing the same thing. But some of them look ready to bloom:

The other day, my husband called my attention to bloated buds on a Star Magnolia tree that looked ready to burst. (I didn’t have a camera with me, and we were in a hurry so I didn’t take a shot with my camera phone. Note to self…)

Anyway, he was concerned that they would bloom before the winter. I must admit it made me pause, too, though I know that many plants carry fertile, dormant buds through the winter. I just couldn’t explain how or why they do it.

So I did a little research and found a very detailed explanation from the University of New Hampshire Cooperative Extension.

Here are few interesting facts:
  • Buds are dormant embryos packed into a protective outer scale. The period of winter dormancy lasts several months, and most native northern plants don’t break dormancy during a fleeting January thaw. Tricky!
  • 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.
  • 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.
  • Most dormant flower buds have air pockets between the many layers of embryonic flower tissue—a layering system that provides protective insulation. This is similar to what skiers and other winter sports enthusiasts do to keep warm—dressing in many layers to trap air.
  • 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.

Back to the Star Magnolia: This spectacular plant has an extra winterizing strategy. The fuzz on its ample buds traps air that helps insulate the flower buds from the cold.

The buds of all these plants look so vulnerable, especially when I think about the subzero weather that’s just around the corner. But they’ve survived for years after repeated blasts of extreme cold and terrible blizzards. They’re definitely hardier than I am.


  1. Dear Beth, What a most interesting posting, full of information that is new to me. I love the idea of the Magnolia buds wrapped in fur coats against the winter cold. Nature is so marvellous in these small details which are so easily overlooked.

    I am so pleased that I have come across your weblog and am thrilled that you have added mine to your 'Favourite' list. I look forward to our continued dialogue in this ever intriguing world of gardening!!

  2. Hello Beth

    That old saying that you learn something new everday, is certainly true for me and your excellent post. I supposed that i had never realyy considered how these buds survive winter and took it for granted that they just did. If we take the time too look carefully enough mother nature can teach us som many things.

  3. Thank you both. I'm learning so much from you and other bloggers, too!