Drastic changes in temperatures challenge plants’ ability to adapt

If there is a common thread that runs through Maine weather — winter, spring, summer and fall — it must be changeability bordering on the perverse. Witness the growing season of 1993, which began with near-record cool temperatures in May and early June (hardly anyone could get a cucumber to grow during the period), followed almost immediately by a spectacular heat wave and mini-drought.

Humans find these sorts of changes stressful as our bodies can adapt only so quickly to major fluxuations in temperature, and the same holds true for garden plants. Although most crops can grown over a range of 30 degrees or so, sudden changes in average temperature really put the average plant’s adaptive ability to the test.

As I write this column, the weather has taken yet another precipitious turn, from summer heat to crisp, fall-like coolness. (At least it stayed warm long enough to get a good crop of melon vines going and set a few pepper fruits.) Who knows what the temperatures will be by the time you read these words, eight days hence? Maine weather makes garden writing almost as challenging as garden growing!

Annuals in window boxes or growing in the garden may have bloomed themselves silly during the heat wave, and if your schedule didn’t allow for frequent dead-heading (removal of spent blossoms), now is the time to make amends. Cut or snap off anything that looks like a seed pod or fruit as well as any withered flowers, leaves and stems. Next, take a step back and look at the plant to assess its overall condition. If there is new growth coming around the base of the plant, it might be wise to interrupt its blooming period by shearing back to the best-looking new shoots. Usually this results in only a week or two of flowerlessness, followed by a glorious second season of color. This technique applies more to fast-growing plants such as pansies and petunias than to slower developing crops like geraniums and New Guinea impatiens which require only dead-heading.

Of course, water is the key to any plant’s success or failure. Container plants, with their limited root run, require faithful daily or even twice-daily attention during hot weather. Once-a-week applications of diluted fertilizer solution (Miracle Grow or equivalent, 1-2 teaspoons per gallon) are far better for your plants than less frequent applications of full-strength or super-strength (if a little is good, a lot must be better, right? Wrong!) fertilizer. If you’re handy with kitchen chemistry, you can mix up a stock solution of fertilizer in a jug (kept labeled and out of children’s reach) containing one cup of dry soluble fertilizer in a gallon of water. Mix 1/3 to 2/3 cup of the stock solution with a gallon of water in your watering can and you have a finished strength of 1-2 teaspoons per gallon.

When watering the lawn or garden, please remember that a good soaking once a week is much more efficient than frequent light waterings. Use a bucket or two placed strategically in the sprinkler’s spray pattern to determine when you have applied the equivalent of one inch of rain. To conserve water, run the sprinkler early or late in the date, during the night or on cloudy days. There’s no sense in losing 10-20 percent to evaporation.

If you’re trying to grow cool-weather crops like lettuce and radishes during the hot months, consider a partial shade over the row. Snow fence, cheese cloth or any other holey substance that passes 50 percent or more sunlight will go a long way towards curing the bitters in lettuce and the hots in radishes.

Michael Zuck of Bangor is a horticulturist and the NEWS garden columnist. Send inquiries to him at 2106 Essex St., Bangor, Maine 04401.