Aesop told about a shepherd boy who got so bored and lonely, spending all day on the hill with his sheep, that he decided to stir up some excitement.
“Wolf! Wolf!” he yelled to the townsfolk below. “A wolf is trying to attack the sheep!”
People came running with rakes and pitchforks to chase away the wolf. But there was no wolf – not even a paw print. “You must have made a mistake,” they said, and went back to their work.
But a few days later, bored and lonely again, the boy yelled “Wolf! Wolf!” and they all came running again.
What fun! Maybe fun for the boy, but not for the townsfolk. They were angry at being called from their work.
He tried it a couple more times before the townsfolk decided to just ignore him.
And that's when the wolf DID come.
The shepherd boy called for help, but nobody came.
He lost two sheep – and his job.
Every since then, when people think someone is sounding a false alarm, they say “He is just crying 'wolf.'” And they ignore him.
Though they always worry that some day he might be right.
We have unpredictable winters here on the plains, balmy spring weather one day and arctic cold the next. How do the trees and bushes know when it is really safe to bud out? When a sunny winter day seems to call “Spring! Spring!” how do they keep from dropping their winter protection too early, when a late hard frost might kill the new growth?
Plants have two strategies to help them wait until spring really comes.
As autumn days get shorter and cooler, active growth slows down and buds form for the next year. A certain number of cool days will induce an inactive (dormant/sleeping) state from which even a mild spell can't wake the plant! This is called “endodormancy.” An endodormant plant can survive very low temperatures and drought. It will sleep in this state until it has experienced the proper number of “chill hours” indicating that winter has probably passed.
Only then does it go into the second state, “ectodormancy,” where activity is again possible on mild days but slows to nothing on cold days. Once it has gone into ectodormancy, it risks damage from a late spring freeze. Gradually it will bud out, and resume active growth.
Different plants have different light/cool requirements for going into endodormancy, and require different numbers of chill hours before they can come out. What could possibly go wrong?
If you plant temperate zone trees like peach or hickory in the tropics, they will grow just fine... and keep on growing... never going dormant.. and never flowering. They did not receive the signals (shortening day, cooler temperatures) that induce endodormancy.
If you made sure your fruit trees went into endodormancy before you shipped them to the tropics, they would not get the chill hours they need to shift into ectodormancy where they can respond to the tropical breezes. They may sleep their lives away.
Different varieties of the same fruit even have different chill hour requirements! Farther north, where winters are long, a variety with a low requirement could soon pass into ectodormancy but the chilly weather would keep it safely asleep until spring truly comes. Around here, though, it's good to choose one that needs many chill hours: while waiting to collect them, it will stay safely dormant despite the temptations of early warm spells. You won't lose your peach crop to a late freeze.
Some state departments of agriculture have researched the chill hour requirements of different varieties of economically important fruit and nut trees. This information is very useful to orchardists and home gardeners.
Of course native trees and bushes use these strategies too! This spring, notice that after imported trees have already budded out, many native trees (oak, persimmon, etc) are still asleep. They don't want to be fooled when spring-like warm spells call “Wolf!”