It has been a typical October day, crystal clear and sunny, but the warmth of the sun has been noticeably tempered by the chill wind. There have been a few slight frosts which have nipped the more tender plants of our gardens, but tonight’s weather forecast seems to spell the end for the still living plants and flowers. The forecast warns that a killing frost will take place.
The weather map shows that we are under the influence of an intense high-pressure area which has originated far to the north and has brought with it clear skies and cool temperatures — an ideal condition for a killing frost. We hurry in the last of the vegetables and hopefully place newspapers over some of the remaining flowers.
What are the processes that go on during the dark hours of the night that causes the morning to dawn on whitened lawns and gardens? Suppose we spend the night out of doors—in fancy of course—and see how the Creator of heat and cold suspends again for a season the growth and development of all grass, herbs and trees. It is still early in the evening as we glance at the thermometer which is already down to thirty-eight degrees. This shows that the radiation of the stored sun heat has already begun in earnest. If our eyes could see them, we would perceive tiny heat waves, travelling out from every object around us, including ourselves. As we look up at the blazing stars we know that there is nothing to stop these heat waves. If there were a cloud layer, radiation would be greatly slowed for much of it would bounce back toward the earth.
Let us now look closely at the topmost leaf on this maple tree. It is about 35 feet above the ground. Suppose now that the air surrounding this leaf, upon which our attention is fixed, goes no lower than thirty-three degrees during the night. The leaf contains moisture and as the evaporation of moisture tends to cool, we find that our leaf’s temperature drops a trifle lower than the air surrounding it. This slightly cooler air, being more dense than the surrounding air, begins to settle. This goes on about every leaf, so that by the time all these tiny trickles of cooler air converge there is a decided drift ground ward. When it reaches the ground surface it begins to spread out like a pool.
Our maple is located on sloping ground so that if again we could see this cold air we would notice another flow coming from higher ground and joining our pool. Where at first it was but a film, it has now thickened and caused a more rapid radiation of objects covered by it, which in turn increased the coldness of this frosty layer. At the bottom of this slope on which we stand is a level field. It is the lowest point in our vicinity. The dense cold air now begins to move toward this low spot, much as a stream would fill a hollow space to form a lake, only now we have a lake of freezing air and if this low spot be a muck farm, as is often the case, we find our heaviest frost damage there. To plant an orchard, for instance, in a valley would subject the blossoms to a much greater degree to frost damage than if the orchard were on a hill.
The U. S. Weather Bureau has prepared tables of average first and last killing frosts and they are well to consult when we plant our more tender flowers and vegetables. In perusing these vegetables we were amazed at the difference of the growing season between last and first killing frosts. For example, Aroostook, Maine, has its last frost June 7 and its first September 22, while Los Angeles, California, has its last January 3 and its first December 28! The former has one hundred seven growing days while the latter has three hundred fifty-nine!
As we awaken and see this white hand of death covering all the plants we are saddened for we know that the beauty of yesterday will be dead and black today as the sun reaches the whitened plants and flowers. But we are Christians and all of God’s works in nature have lessons for us. These plants are not dead! They live in seeds and spores and roots. Neither are we dead when death strikes us down as the frost the tender plant. Next spring the plants will rise again and in the eternal Spring of the new creation we also shall rise to die no more.