Growing degree-days are like a scorecard that helps farmers and scientists keep track of how warm it is outside. They use this scorecard to figure out when plants will start growing and when they will be ready to pick.
Here's how it works: every plant needs a certain amount of warmth to grow. One day that's not too hot or too cold doesn't make much of a difference, but if you add up all the days that are warm enough (above a certain temperature), you get a growing degree-day.
For example, let's say one apple tree needs 1,000 growing degree-days to start making apples. It's been warm enough for four days, and each of those days were worth 10 growing degree-days. So, the apple tree has accumulated 40 growing degree-days so far.
Farmers and scientists can use this information to predict when fruits and vegetables will be ripe for picking. They can also plan when to plant different crops based on how many growing degree-days they need to grow successfully.
So, growing degree-days are like a special thermometer that helps us keep track of how warm it is for plants.