Monday, March 26, 2012

This Bud's For You

So the big question is, how far did our Boston plants break dormancy last week? We had an extended spate of very warm days, bright sunshine, and all the ingredients necessary to bring out the flowers, and to an extent, the leaves. Our magnolia, our forsythias, and all the cherry trees in the neighborhood were out in full bloom. Now the weather has gone back to March. The next couple of nights we should see below freezing weather. What happens to the plants?

Lilac Buds

The short answer is, it depends what plant it is. The flowering plants like magnolias don't depend on their flowers to survive. Reproduction, normally the role of flowers, is obviously not essential in our urban garden environments.


But the leaves are another story. Have you ever noticed that on most of the trees, it's the flowers that come first and later the leaves? Plants in the temperate and cool zone have evolved so that the leaves come out of dormancy last. And there's a reason for this. A late frost will kill off young leaves, depriving the tree of nutrients and potentially killing it.

Sycamore tree disease

So let's look at the question a little closer. Excluding the flowers, which we've already callously determined as unnecessary, what about the leaves? Again, it depends on the species. Most of the shrubs and trees I've looked at still have their leaves tightly packed in buds. They may not have even begun the process of breaking dormancy. But in case they have, two things might still protect them.


First, structural anatomy. If you look carefully at most angiosperms (flowering plants) you will see that in addition to the main bud, which breaks dormancy first, there is at least one other bud held back in reserve. The beech leaf below is a perfect example.

Beech leaf

...or this birch.

Birch leaf

Many layers of vegetative covering also protect the young buds. They are slow to lose these layers.

Lenticels and Gas Exchange

Juglans regia

A more complicated and perhaps less well understood protective phenomenon is the suite of metabolic and chemical conditions each plant has evolved into. Buds sheathed in a waxy coating are one example. They are full of anti-freeze and surrounded by anti-freeze. And they are well protected until the cascade of dormancy-breaking reactions starts.

Woven willows

So even though the weather has unpredictably swung back from July to March, I am pretty certain that thanks to millions of years of experience with this sort of thing, the plants have it in the bag.

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