Grapevines, like many other plants and most people, love heat — to a point.
In the early summer, when daily temperatures top out in the upper 80s and low 90s, their rapid progress is palpable. One might even swear it is actually possible to see their bright-green shoots lengthening in the vineyard during what is known as the “grand” period of vine growth.
This love affair with the heat extends only so far, however. When afternoon readings climb into the scorching upper 90s and low 100s, as has been the case recently in the Walla Walla Valley and elsewhere in Washington, grapevines — much like the humans who tend them — begin to adopt avoidance strategies to help conserve water.
Leaf angles relative to sunlight become more acute as the plant attempts to lessen the heating effects of incoming solar radiation. Stomata — the tiny pore-like openings in the underside of leaves through which carbon dioxide enters to be converted, with water, into carbohydrates and oxygen during photosynthesis — close to conserve moisture and maintain the process by which vines maintain a steady flow of life-sustaining water and minerals from the roots to the leaves.
In short, when stomata close, growth stops. And if grapevines were mobile, at this point that they would seek shady shelter — as do humans — from the stifling heat.
During long, dark and frequently very cold Walla Walla winters, I have often found myself dreaming longingly (as do perhaps our vines!) for such days of sun and warmth.
But as I have become older, when those summer days arrive as they now have it quickly becomes obvious that my former tolerance for even a moderate amount of heat has evaporated like a sidewalk puddle after a July thunderstorm.
Growing up in Baltimore, summer heat and humidity were a given, and before Mom convinced my very frugal Dad after years of pleading to invest in air conditioning, that seasonal combination became woven into the very fabric of life. Its annual arrival was expected — almost welcome even — as it became synonymous with lazy, carefree days as did the regular and bitter complaining about it.
Sometimes, during the frozen months of the year, my thoughts turn to the cactus-studded Sonoran Desert of Tucson, where nine years as a nearly-perpetual student at the University of Arizona instilled in me a deep appreciation for the cosmetically enhancing qualities of the relentless high-desert sun. It got to the point where my class schedule was arranged around peak tanning hours of mid-day, even when the mercury had risen well past the century mark.
I’ve come to regret that practice, with an annually increasing pile of dermatology debt from the damage incurred in what now seems as foreign and unappealing as a leisurely walk over a bed of hot coals.
More recently, my wintertime heat-related musings are centered around the sweet, intoxicating, earthily fecund smell of a South Carolina July. Bathed in the heady aromas of unbridled vegetation supported by a breathtaking combination of heat and humidity, it’s a combo that only the Deep South can cook up.
It was in that greenhouse-like environment — where even the slightest movement induces a flood of perspiration that causes one to obsess about the glories of a cool shower — that I had the great good fortune to meet the love of my life, with whom I am now as entwined as side-by-side vines whose tendrils grasp tightly in mutual support.
For those who take a less magical view of the recent heat, some relief is on the way. A low pressure system is forecast to take up residence near the mouth of the Columbia River and induce a modest cooling trend as marine air slowly filters eastward over the Cascades into our area. Daytime highs should recede to more normal levels — mostly in the upper 80s — with only a slight chance of an isolated thundershower or two to disturb your summertime idyll.