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FeedMeet Me in St. Louis
New rules guide almost-Zone 5 gardens
By bonnie blodgett
Photo by Judy White, www.GardenPhotos.com
Gardeners don’t need convincing that global warming is for real. We’ve seen what the new Zone 4 does to plants. What we’ve lost in a reliable, if tad constricting, plant palette, we’ve gained in uncertainty. Will a sudden cold snap after a long, warm fall catch my plants unawares? What about freeze-thaw cycles? Will shallow-rooted plants get pushed right out of the ground if there’s no snow cover?
Delusional gardeners like myself can’t help seeing a silver lining in climate change. Now I can grow Japanese maples. Garden centers are feeling the itch, too. Did you notice you couldn’t turn around in a nursery last summer without bumping into a potted Acer palmatum ‘Emperor’? I don’t know anyone who still holds to the idea that Zone 5 plants are off limits. OK, ‘Emperor’ is rated hardy to Zone 4, but is that the new or old version of Zone 4, and which ‘Emperor’? The cultivar is marketed as both ‘Red Emperor’ and ‘Emperor 1’. My advice is to buy a big plant, preferably in a five-gallon pot. Minnesota winters may be warmer but we still live perilously close to the North Pole. At any moment one of those bone-chilling (and Acer japonicum killing) Arctic fronts can move in and send you rushing to the hardware store for a roll of burlap. And while you’re there, can you pick up a space heater to thaw out the frozen pipes in my back bathroom?
More complicated is what happens to “old reliable” plants that struggle when winter doesn’t do its normal, ungodly-cold thing. Plants are creatures of habit. Their exquisitely sensitive biological clocks respond to seasonal cycles. Perennials, for instance, switch their priorities from survival of the species (summer seed production) to keeping themselves alive. Timely changes give them the heads up they need to close the leaf production factory and start storing energy in their roots. Woody plants likewise shouldn’t be encouraged to put on new growth toward the end of summer, when shorter and cooler days are telling them it’s time to sheathe leaf and flower buds that will open in the spring. Tender young shoots are likely to freeze when winter comes early, and an early thaw is the usual culprit if your magnolias fail to bloom in spring.
Because I can’t resist trying to grow marginally hardy plants, and because I’m naturally a worrywart, I try to play it safe. I find a sheltered location for my “experiments,” and I get the plants into the ground in spring. That way, their roots have all summer to settle in. In fall, I become a hovering mom; I bundle them up well. My dear little Japanese maple ‘Crimson Queen’ is smothered in leaves encircled by a wire mesh “cage.” A bit of straw goes on top. Mulch keeps the soil temperature relatively even, just as snow does (or doesn’t, as Mother Nature chooses). Given her capricious mood of late, I’m not counting on anything.
How do I decide a plant is worth all the fuss? Wish I could tell you there’s a science to it. If I hear about (or see in person) a truly unusual and captivating specimen, chances are I’ll give in to my inner child. I must have it. Now!
Here are a few varieties I’ve decided are worth the gamble:
» Wisteria.
Chinese wisteria won’t survive here, but Japanese wisteria (reputedly less invasive with longer flower racemes) just might. Here’s the confusing part: Wisteria floribunda goes by the common name Japanese wisteria and the hardiest is a Minnesota product named ‘Aunt Dee’, bred from a Kentucky native. The trouble is, its cute little lavender flowers almost-but-not-quite resemble the real thing. Instead of dangling like pendulous earrings through the overhead slats of your new pergola, they sort of pop out of the vine’s dense leaves in all directions. The native Wisteria macrostachya ‘Blue Moon’, on the other hand, is said to produce foot-long racemes from June through September. ‘Blue Moon’ also reputedly withstands both the old and new versions of Minnesota winters, but here’s the rub: It must have full sun in order to do that and produce all those flowers in the summer months. Seed production is the first thing to go when a plant is stressed, and that means flowers. With ‘Blue Moon’ you can expect either feast or famine. It’s a gamble I’m willing to take.» Rose.
The Meidiland roses (‘Ferdy’, ‘Bonica’, ‘Royal Bonica’, and ‘Sevillana’) need winter protection, but deserve every bit of it. David Austin’s English roses are a bit dicier, but so beautiful and fragrant that I’m thinking of taking the plunge as soon I as find an available swatch of microclimate. Of all the great Griffith Buck roses bred in Iowa, the hardiest is ‘Carefree Beauty’. I’ve grown others in the Buck family, too, with great success. Nearly hardy here, hybrid tea roses are worth making a winter igloo for: ‘Chicago Peace’, ‘Fragrant Cloud’, ‘Olympiad’, ‘Mister Lincoln’, ‘Summer Dream’, and ‘Tropicana’.» Buddleia.
This is technically a subshrub, meaning that like Russian sage, it is part woody and part perennial. In Zone 4 the hardiest of the buddleias will die back to the ground in winter, like a perennial, and return (in its own sweet time) during the summer months. The key is to be patient. It will flower on schedule in late summer no matter how wretched it looks in June unless the winter killed it—always a possibility. As with all envelope pushers, the more winters a buddleia withstands, the tougher it gets. Try ‘Black Knight’ if you go for deep purple flowers and ‘White Profusion’ if you like white. Each is quite hardy—for a buddleia.» Maple.
I’m talking about the smaller ornamental varieties like the aforementioned ‘Emperor’, a Japanese maple. Sightings have been reported throughout the Twin Cities of the following borderline hardy maples: Acer shirasawanum ‘Autumn Moon’, Acer japonicum ‘Aconitifolium’ (its Japanese name, ‘Maiku Jaku’ means “dancing peacock”), Acer circinatum ‘Sunglow’, a vine maple cultivar, and Acer palmatum ‘Robinson’s Red’, a Japanese maple cultivar.» Sambucus.
If you happen to see a plant that looks amazingly like a Japanese maple—finely dissected leaves, delicate form, rich color—it might be ‘Black Lace’ sambucus. This eye-catching new shrub is an elderberry, rated Zone 4 (elderberries are natives). It’s also new to these parts, having grown up in England. I planted one last spring. It’s being sold as a Japanese maple with a bonus: pink flower clusters and purplish gray leaves and stems. A handsome combination, which I hope to see again this summer. A similar, but coarser-leaved and probably hardier, version of ‘Black Lace’ is ‘Black Beauty’. Both are lovely.» Hydrangea.
With lovely cultivars like ‘Annabelle’ and ‘PeeGee’ proven reliable, why go looking for trouble? I think you know. When I read that climbing hydrangeas are a Zone 5 plant and require root cover in winter, I almost shied away. My vine turned out to be the toughest (and probably the prettiest) plant in my garden. The much touted, Zone 4-rated ‘Endless Summer’ is a big leaf hydrangea, a species normally hardy only to Zone 6. It disappointed some northern gardeners because it tends to die back and thus can’t deliver on its promise to bloom on old as well as new wood (old wood means early flowers). I’d rather risk disappointment for the H. paniculatas ‘Limelight’ (from Holland) and ‘Tardiva’. If money were no object, I’d even try growing an oakleaf hydrangea, prized for its fall colors. It’s rated Zone 5, but is less hardy than climbing hydrangea. One cultivar that just might make it in a sheltered spot with root protection is ‘Snow Queen’.» Evergreen.
Taxodium distichum’s common name is baldcypress. It’s quite hardy. A bit less so is Cercidiphyllum japonicum ‘Perdula’ (weeping katsura). And then there’s Chamaecyparis nootkatensis ‘Jubilee’, and ‘Pendula’, both Alaska cedars. Yeah, right. It’s rated to –10 degrees to –20 degrees Fahrenheit.This one’s for the risk taker. I can’t wait.
Bonnie Blodgett publishes The Garden Letter, and is writing a book about smell.
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