AS WE NOW complete our first full week of autumn and evening temperatures have dropped significantly, let us re-familiarize ourselves with our infamous friend, Jack Frost.
The first frost or two always taunts me because, for most people, it kills large parts of their garden and then the weather turns nice, and doesn’t freeze again for several weeks.
Understanding frost, along with some tricks on how to protect your plants, should greatly aid all of us in meeting that plant survival goal of Nov. 10 or beyond.
How frost is formed
Whenever two adjacent objects have unequal temperatures, the colder one always gains heat at the expense of the warmer. At night, the Earth receives no radiant heat from the sun and thus loses heat to the air.
If enough heat is lost, the surface temperature (soil line) drops below freezing. When the humidity is high and the night temperatures are below the dew point (the temperature at which the relative humidity equals 100 percent), but above freezing, moisture condenses and dew forms.
If the air temperature drops below freezing, and below the dew point, a “white” frost forms.
If the air temperature is above the dew point, but below freezing, a “black” frost occurs.
Black frost is more damaging because of internal freezing and the leaf suffers. Black frost can be lessened by keeping soil moisture (humidity) high.
You will know a black frost because the foliage will appear very darkened in the dawn light.
When to expect frost
Frost or freezes can follow almost any type of local weather. Since they are a function of heat, they become more likely as fall progresses and soil temperatures drop.
Although I hate predicting weather, and those sources that try to predict months in advance, I do strongly believe our frost will come earlier and harder.
This is solely because of the unseasonably cool summer we have had here on the Peninsula. Our warm days are significantly off this summer and so it will take less of a cold front to cause a freeze.
How to protect plants
Moisture in the ground tends to prevent warming of the ground during the day. It also tends to prevent a large fall in temperatures during the night.
When the dew point is reached, the latent heat given up by saturated soils checks the rate of cooling.
If a hard frost is moving in when the abundant surface moisture freezes, the liberated heat from the water checks the falling air temperatures.
It is complicated physics, but to the gardener, it means a strong possibility of only a light frost and cool-tolerant plants could care less.
So trick No. 1 to remember, when you believe it is going to freeze, water your garden to saturation. Make sure you see some puddles.
The next method of frost protection is the most common, covering your plants. Be it colored plastic, cloth, tarp or sheet, throw that baby over the tender plants that need protection.
Now the purpose of all coverings is to keep the cold air off the leaves as much as possible.
Fortunately, the first few frosts are accompanied by several weeks of nice weather and one only has to cover for a couple of days.
Now is the time to prepare your areas where you are to cover.
Drive any kind of stake next to your plants, since coverings that lay directly on the plants crush them. I have seen numerous times for the plant to be saved from frost, but the weight of the dew-soaked sheet ruined the plant. Also, having an air gap around the plant helps trap the heat of the ground and is a superb insulation.
So trick No. 2 — make a collection of materials you will use as a cover, drive in the ground whatever will hold that material just off the plant, and toss that cover on and off as the frost comes and goes.
Trick No. 3, and really just a version of cover, is to put your plants indoors. It is so simple and so overlooked. The few baskets and individual plants, along with container planters, can easily be moved in and out of a garage, porch, entryway, even the wall of a carport (but only if it has a heated wall).
This will easily give you a few more weeks of enjoyment and the time spent handling the plants can be spent pinching or fertilizing.
And now, I have saved my best trick for last, watering before and at dawn.
It is just so ironic that, as I planned and wrote this column, there is emerging a light frost.
As a gardener, from a family of gardeners for generations, I am prone to wake up before dawn.
Walking out to the shop where I write these columns, I could feel the preparations for the arrival of Jack Frost.
In fact, I just returned from a break in writing, during which I drove up to the top of Black Diamond road and viewed several examples of isolated black and white frost.
Trick No. 4: If, and only if, you go out to your plants before dawn and soak every plant to dripping wet, you can protect your plants from light frost (28 to 32 degrees). In light frost, the chloroplasts and other cells are in a state of limbo so to say.
When the sun shines on them, the crystallizing damage of the frost causes the cells to degenerate. If, before dawn, water is applied, that un-thaws the cells before the light phase of photosynthesis begins.
Please remember that you need to run the sprinkler or water the area until after sunrise. Watering must be done until after the temperature is above 32 degrees.
This has probably been more than anyone cares to know about frost, but be warned, this Frost 101 course will be revisited in the spring when frost is used as a valuable gardening tool.
Until then, protect your prize container plants, showing flowers and tender vegetable plants. They can all easily make it well into November.
Until then … stay well all.
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Andrew May is a freelance writer and ornamental horticulturist who dreams of having Clallam and Jefferson counties nationally recognized as “Flower Peninsula USA.” Send him questions c/o Peninsula Daily News, P.O. Box 1330, Port Angeles, WA 98362, or email news@peninsuladailynews.com (subject line: Andrew May).
