Unraveling The Mystery Of Climate Zones



Garden catalogs are full of pictures of wonderful plants that lure the gardener into visual fantasies of this year's growing season. Determining if a plant will be suitable for a Rim country garden depends on information the gardener needs to decipher before placing the order.

Unraveling the mysteries of climate zones and plant needs helps to eliminate frustration and disappointment, which results from choosing the wrong plant for the wrong spot.

Since 1953, growers have used the USDA "Cold Hardiness Zone" map to determine whether a plant will withstand the winters and growing season length of a given area. While serving as a useful tool, this map deals only with average low temperatures but many other considerations determine if a plant will flourish in a given area. Plant descriptions frequently mention a "zone" number, which indicates the plant will withstand the winter in that zone.

The American Horticultural Society has recently published a "Heat Zone" map, which shows the entire country in colorful bands of summer temperatures for various lengths of time. The AHS is encouraging growers to tag their plants with a heat zone number, which indicates the plant will grow in an area with a given number of days over 86 degrees.

Sunset Publishing Corporation, in tandem with the University of California, has divided the western U.S. into yet another set of climate and growing zone classifications. These take into account rainfall, coastal fog influence, summer temperature highs, length of growing season and humidity. And then, to add to the mix, as explained in previous articles, Xeriscape gardeners use their own set of numbers for where to grow each type of plant.

According to the USDA, we are located in Cold Hardiness Zones 6 to 7, which means our minimum low temperatures can be as low as 10 degrees Fahrenheit. The AHS tells us we are in Heat Tolerance zones 7 to 8, meaning we can have between 60-120 days above 86 degrees Fahrenheit.

The USDA and AHS maps are available in many garden publications and on almost any garden site on the Internet. Sunset zones and explanations are available in the Sunset Western Garden Book, and are detailed enough to be a better measure of the peculiarities of our complicated climate patterns.

The rim area is listed at Sunset Zone 2. Plant selection can be streamlined by: Noting the botanical name of the plant and variety if applicable; looking the plant up in the Sunset Western Garden Book; determining if the right location is available for planting; and last, but most important, the water requirements of the plant.

When choosing a plant from a catalog, or browsing a nursery, be sure to check the detail information regarding the growing conditions required by that plant. This part of Arizona is classified as the Piñon-juniper belt. This life zone receives no more than 25 inches of rainfall in a very wet year, soils tend to be rocky and sandy, and humidity is normally very low. Rainfall under normal conditions is about 18 to 20 inches, and comes in concentrated amounts during short periods of time. Cold winter nights and blistering summer days are the norm here, and the plants that thrive under these conditions are highly specialized to do so.

Considering the drought conditions during the past few years, and limited precipitation amounts forecast for this year, making sure to choose the right plant for the right spot is more important than ever before. Managing water supplies to provide adequate amounts for household use and hygiene, and eliminating waste out-of-doors is more important today than ever before. Gardeners who choose plants appropriate to this climate and limited water supply will encourage merchants and growers to stock and provide information on how these plants can best be used in the Rim country garden.

It is possible to grow many different plants here that have originated in other areas, but impractical if artificial conditions need be supplied to keep the plant healthy.

Plants that are well adapted to upland Arizona growing conditions are easy to grow, require a minimum in terms of maintenance, fertilizer, and water.

In-between cold spells, our garden maintenance chores this month include pruning of all dormant fruit and ornamentals. Use "Hi-Yield" dormant oil spray on deciduous fruits and ornamentals to kill over-wintering insect eggs and disease spores. Pull large weeds as the ground is soft, and the root system should be easily removed. Remove heavy snow with a rake or broom to prevent branches from breaking.

Supply water for birds who will also gobble up suet, fruit and seed. Attracting birds to home gardens helps keep insect populations in check, and the ecosystem in balance.

Barb Bourscheidt is a longtime resident of Payson, a member of the Rim Area Gardeners and a participant in the Gila County Master Gardener program. She serves on the board of directors of the High Country Xeriscape Council of Arizona, and she researches and writes articles on the subject of water conservation through creative landscaping and climate-appropriate gardening techniques.

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