The dramatic changes in our planting zones
Early blooms and cold snaps turn gardeners’ lives on end.
This is the time of year to think about planting trees. It’s a powerful, important and often a genuinely fruitful thing to do. Planting a tree is also a long-term commitment. It requires a deep look into the future, and given the way the climate is shifting around us, it’s like aiming at a moving target you can't even see.
The U.S. Department of Agriculture’s plant-hardiness zone boundaries are marching steadily northward, as can be seen on a map loop. In the 15 years since my friend Tom McCamant planted his peach orchard in northwest Montana, his land has been reclassified from Zone 5b to 6a.
It wasn’t long ago that if you wanted to grow peppers here in Montana, you had to plant them in a greenhouse. Now we get outdoor peppers every year. Ranchers who used to get two cuttings of alfalfa are now getting three. Pasta makers are already looking northward, in search of the next hotspot for the best durum wheat. Some wine grape growers are preparing to move north as well.
The plant hardiness zones are based on overnight lows, which determine both the growing season for annuals and which trees can hang through the depths of winter. These constraints can be increasingly finagled with the help of a growing arsenal of clever tricks that farmers are coming up with to control the climate around their crops.
Such measures can help extend the season for greens deep into winter, or set up an early start for next year, or allow risk-tolerant growers to take a chance on some exotic thing that shouldn’t have any business growing here. At the farmers market in Missoula, Montana, you can now get fresh ginger along with okra, artichokes and freshly roasted green chile (not necessarily a serving suggestion).
“Most of the country has moved up a zone from where they were in 1980,” McCamant says. “The best opportunities in agriculture right now are in marginal spaces.”
McCamant would know. When he was planting his Forbidden Fruit orchard, extension agents and agriculture academics told him that peaches were at best a marginal crop in Montana. Now, his many varieties, some of which are grapefruit-sized, have become a prized delicacy in the region. The lengthening summers and shrinking winters have generally been good to his orchard, in terms of quantity as well as quality. Bumper crops have become the new normal at Forbidden Fruit.
“But it’s a double-edged sword when you bloom early, because you still get those cold snaps. You increase the chance of frost damage,” McCamant says. “Weather in spring and fall is a lot more unstable these days.”
McCamant has a frost protection system that consists of a series of fans called “cold air drains,” and the occasional sprinkler to form a brief line of defense against frost. Last year, he spent more time running frost protection than sleeping. He operated it for 14 nights between April 1, when the peaches bloomed, and April 20, when they used to.
But a March bloom would be tougher to manage for his system, which can only buy a few degrees. And a February bloom would mean he could take the summer off, unpaid.
“Februarys have been warming faster than just about any other month,” McCamant noted. “Having an early bloom once in awhile is to be expected,” McCamant says. “But having two early blooms in a row, that’s a first.”
While there’s no doubt that warmer days are coming, it’s less clear what to do about it. My yard is home to a Chicago fig that is rated for zone 5, my current hardiness zone, and a Russian pomegranate that supposedly needs a zone 6, the edge of which is a few miles to the west and approaching. At the rate we’re going, we might already be there.
Messing around with hobby plantings like this isn’t a substitute for getting out there and doing something about saving the planet. But if there was any lingering doubt that things are changing, watching the trees might set that aside. Though some new plants will grow, we can also expect others to die. Sugar maples, for example, are more vulnerable to disease during warm winters, which give many pests the upper hand as well. Pollination patterns are also changing.
With all of that in mind, it’s time to order trees. No more pomegranates and figs for me — at least until the first ones prove themselves. Some peach trees are in order, and McCamant recommends a variety called “Reliance.” I’m going to order a plum tree, too, albeit with some trepidation: It’s a cold-weather tree.
