Since we are snowed in for the winter, it is a good time to catch up on some reading. I just finished reading "The Gardener's Gripe Book" by Abby Adams. The subtitle is 'Musings, advice and comfort for anyone who has ever suffered the loss of a petunia'. Abby is obviously an avid gardener (10 ½ acres in zone 5 New York), but she claims that she is not an expert, nor does she have a green thumb. She wrote the book for people who find gardening a fascinating, maddening, frustrating and an absorbing endeavor. This is a very funny book that covers all aspects of gardening, beginning with its history.
A person could spend hours on Internet gardening sites. I spent some time on Northscaping.com and read a few articles by Jim Kohut on winter hardiness. So far our 2009-2010 fall and winter season has been an up and down affair temperature wise. September was warmer than average, October colder, November warmer, December colder, but perhaps January is going to be average, if there is such a thing. It makes me wonder how our perennials, shrubs and trees are surviving. Were they able to harden off properly and was there enough snow cover before the frigid weather hit?
Overwintering trees and shrubs is probably the greatest challenge northern gardener's face, according to Jim Kohut. The majority of their growing parts are exposed and unprotected all winter. The living cells have to survive the cold without freezing. They have internal 'antifreeze' that prevents ice crystals from forming and rupturing their membranes. This is only effective down to a certain minimum temperature and it is a core indicator of hardiness. Select varieties are known to be hardy for our zone or colder.
Wind accelerates the evaporation process, and if the ground is frozen, plants are unable to replace lost moisture. They can die from dehydration or 'desiccation'. Evergreens are especially susceptible and they need shelter from wind by a forest, a building or a temporary burlap screen.
Sun can be a real problem, especially in early spring, when it is high in the sky, and the temperature is still frigid. The sun warms the tissues above the freezing point and then it rapidly disappears. The tissues are exposed to freezing before the 'antifreeze' mechanism can react. Ice forms, killing the cells in a condition called 'sunscald.' The reflection off white snow exacerbates the problem. The solution is tree wraps or white paint on the trunk to reflect the sunlight. Sunlight can also cause the desiccation of evergreens, showing up as brown needles in the spring. A burlap screen alleviates this problem.
Animals are a leading cause of winter injury and even death if they 'girdle' the trunk. Tree wraps and fencing can prevent most of the damage.
So far this year we have not had ice storms, but heavy snow may also cause some damage. Be careful in removing the snow from weighted down branches, as they are very brittle on freezing days.
Perennials are subjected to the same elements, but they usually get protection with snow cover or other mulch. The number one killer of perennials is exposure to the elements, so if your garden is windswept, pile mulch or snow over it. This will also prevent frost heave damage when the ground begins thawing and refreezing.
Some gardeners like to push the zone a little and there are things to consider in doing so. We know that weather is wildly varied from year to year and that the weather is warmer as we go south and on both coasts. Cold air sweeps down from the north and warm breezes flow up form the south. Mountain ranges affect the amount of rainfall. These are all elements of climate and we cannot do anything about them.
We are currently listed as USDA zone 4, although that is an average regional picture. In your own yard there could be areas or microclimates that are zone 5 and those that are zone 3. The south side of a building is warmer than the north, black soil emanates heat from the hot summer sun and green grass has a relative coolness. You may have other nooks and crannies that provide microclimates.
In between these types of climate is a third called the 'mesoclimate.' It is a modification of climate by large cities and towns. Gardeners know that a marginal plant is more likely to survive in the middle of a garden in a suburb in a city than in an open field outside of town. This is the 'urban island effect' or an observation that cities and towns are usually warmer than the outlying regions. Buildings modify wind, and there is greater absorption of sunlight by asphalt. Heated buildings, car exhaust and factory smokestacks are direct heating factors keeping the temperature warmer at night and raising the hardiness zone for plants.
On a less technical note, although equally informative, is the Web site renegadegardener.com. This is written by the very entertaining Don Engebretson, who is a popular lecturer from Minnesota. For the pure fun of it, I recommend that you read 'The 10 Tenets of Renegade Gardening' on the site.
Breitling is a longtime West Fargo resident and avid gardener always in search of new ideas.