Kansas City gardeners can breathe a sigh of relief that we did not reach the forecasted lows last of week of -20. For many years, we have been lulled into thinking that we may have shifted into zone 6. However, it only takes one very cold night to ensure that we are truly a zone 5 area. The plant hardiness zones are based on the average lowest temperatures for a 10 year period. We are about to reset those zone maps if we approach -20 degrees. Plants are rated to their zones based on laboratory tests as well as the experiences of growers in the fields. Plants rated as hardy to Zone 5 generally survive low temperatures of -10 to -20 degrees. Zone 6 plants are only expected to survive to -10 degrees.
Of course, zones are only part of the answer to how your plants will during this cold snap. Zones define large areas, but not small microclimates that exist around your home. If your plants lie in a low lying area or out on a windswept plain, they are going to have considerably more exposure to cold temperatures than if they are nestled in a protected courtyard, along a south facing wall or on the wayward side of a hill.
That being said, many plants in Kansas City are going to suffer from this cold. Dan Simmons of Show-Me Horticulture and I were talking about what effect this could have on plants. We both agreed that a few of the standouts are plants that have started being popular at retail nurseries lately despite being unproven (or proven poorly) to thrive with very cold winters such as this years. A few plants that are going to be strongly affected are southern Magnolias such as Bracken Brown Beautys, crape myrtles, azaleas, rhododendrons and other broadleaf evergreens. These are all plants better suited to Zone 6. They may have done quite well in Kansas City the last several years, but will be well-tested this winter to see if they have enough protection to survive the extremes.
Even a few proven plants will still be stressed. Boxwoods, yews, and many broadleaf evergreens will likely show some damage come next spring from the prolonged cold weather combined with dry winds that we have experienced over the last several weeks. Another group of plants that will very likely show some signs of stress will be some of the ornamental grasses such as the ornamental fescues, the Japanese Silver grasses and the fountain grasses. Some of the larger trees such as Zelkova, Golden Rain Tree, dogwoods and redbuds could suffer some superficial damage to outermost branches as well.
Unfortunately, there is not much you can do to protect your plants now. If your plants went into the winter relatively healthy and unstressed they will have a much better chance of survival than if they were stressed already. Newly planted plants will have a harder time than older, more established plants. The snow that is insulating the ground is the biggest protection we have right now and this can be bolstered if you are inclined to pile snow around the crowns of your most valuable plants. Another option that can be helpful is to build a windscreen around broadleaf evergreens to help protect them. Lastly, to help plants bounce back as much as possible, give them a good slow soaking of water as soon as the ground thaws and repeat at least monthly throughout the winter. This will help immensely as your plants begin to heal their wounds.
This spring will be quite revealing as we learn a lesson of what plants truly are able to survive Kansas City’s coldest temperatures. We will be better gardeners if we observe and learn from what nature teaches this week and choose plants that will thrive in Kansas City even during when it is at its coldest.
If you have any questions, please feel free to visit me at www.HamonsLandscaping.com or posting questions as a comment to this blog post. I enjoy talking to other plant lovers and answering any questions you might have.
|Published on January 12th, 2010||No Comments||Posted by Jeff Hamons|