In the temperature zone with plants

Most of us are familiar with our own comfort zones, and although it is popular to talk of “getting out of ones comfort zone,” it is not so popular to actually do so, nor does one necessarily excel in those less comfortable areas.

Plants also have comfort zones, and fare even less well than we do if taken out of theirs. Because of their will to live, they may survive, but will never flourish.

One of the primary factors affecting plant comfort is temperature.

I’d like to address the temperature minimum, as it is of primary importance and applicable to our gardening environment.

The United States Department of Agriculture (USDA), in cooperation with the American Horticultural Society, has developed a zoning method based on eleven temperature zones.

Starting with Zone One, at below -50 degrees Fahrenheit, Zone Two, at -50 degrees to -40 degrees Fahrenheit, and so on, with each one gaining 10 degrees Fahrenheit, until Zone 11 is reached, at above 40 degrees Fahrenheit.

There is a corresponding map of the United States and Canada available, making it easy to find the zone in which one’s area falls.

Any plant has the best chance of survival if planted in the appropriate USDA zone, and this information, based on plant trials, can be found on most plant descriptions, such as on plant labels, or in seed catalogues or plant identification books.

Having just advised selecting a plant from the recommended zone, let me say that one’s selection is not restricted to that zone, and although such a choice would certainly be the safer, many other plants may succeed in your garden.

A micro-climate of warmer temperature may exist next to the foundation of a house where heat escapes, or near a pond where the water collects heat, or on a slight rise surrounded by lower areas into which cooler air will settle.

Any of these, or other, micro-climates, may increase winter air temperatures as much as two zones.

Also worth noting is that the zone recommendation is not is not always accurate due to variables other than temperature.

An example would be Clematis tanjutica, which in most seed catalogues is rated no colder than Zone Five, -20 degrees Fahrenheit to -10 degrees Fahrenheit, but which is extremely hardy here in the Mat-Su Valley, and should be rated Zone Three, -40 to -30 degrees Fahrenheit.

Another thing to consider, concerning the zoning charts, is that they do not yet reflect the general tendency towards higher temperatures that are currently being experienced worldwide.

On the other hand, choosing a plant from within the appropriate temperature zone does not categorically guarantee its survival, as other factors also influence plant comfort.

A tender young seedling might not survive the winter while a more mature plant may be quite hardy. Northern kiwis, Actinidia arguta and A. kolomikta, for instance, do much better with winter protection until they are three-years old, after which they manage nicely without assistance.

In addition, soil pH and/or moisture, length and intensity of sunlight, length of growing season, rainfall, frost dates, and fill depth, among other things, can all affect plant comfort. A species adapted to bogs usually will not thrive in droughty soil, nor will a drought tolerant plant enjoy a bog. Neither can alkali or acid loving plants successfully change places.

Again, there may be naturally occurring exceptions, or one may be able to create an exception by altering the environment. A natural exception is the native iris, Iris setosa, which occurs in nature in wet open conditions, but will thrive, in the garden, even in dry shade with sharp drainage.

Accomplishing a favorable environment might be done by building a gravely mound to increase drainage, adding lime to change the pH, using a row cover to prevent frost damage, or watering often to counter lack of rain.

Ultimately, it is the individual gardener who best knows what conditions are, or can be created, in his or her own garden. Since the minimum temperature is the factor least likely to be manipulated, plant comfort begins with placing each plant correctly within its USDA zone. After that, proper care and correct conditions will assure that every plant remains contentedly in its own comfort zone.

Hally Truelove is a Master Gardener and Plants Woman who lives and gardens in Wasilla with her two daughters, a handful of cats, a bunch of bunnies, some guinea pigs, a dog and a frog. Contact her at 376-0909.