Cold-Climate

Winter hardiness depends on a number of elements beyond low temperatures, although a record-breaking cold spell can damage even the hardiest plants. In addition, rainfall is often unpredictable in cold climates, and summers may be either prone to drought or wet and humid, depending on where you live. The frost-free growing season is often unreasonably short in these climates — lasting only three to four months — and temperatures jump all over the thermometer.

Winter sun and thaw also pose a significant threat to plants. Many plants that don’t survive winter die because they warmed slightly on a sunny day and then couldn’t readjust quickly enough when frigid temperatures returned. From a plant’s point of view, once frozen, better to stay frozen. Snow serves as the down comforter of mulches. A thick layer of snow keeps the ground solidly frozen and unaffected by constantly fluctuating air temperatures. Flowers tucked cozily under this insulating blanket aren’t tempted to break dormancy prematurely. If a winter warm spell lasts long enough to melt the snow cover, vulnerable new growth gets zapped by the next passing storm. In regions where snow cover is reliable and durable, such weather fluctuations aren’t as harmful.

Perennials that are only marginally hardy in your region may survive winter if you plant them on the north side of a building. In this normally shady location, plants are least likely to thaw on sunny winter days. Gardens in cold-winter climates tend to be high summer gardens. Because the gardening season is short, plants rush to bloom, with most peaking at about the same time. Instead of bemoaning the short season, plan a garden party for mid-to-late summer and amaze your friends from more temperate climes.

Dressing Up The Drylands

In cold-winter/dry-summer climates, summers are devilishly hot, except at higher elevations. Low winter temperatures average –20° F (–29° C) and erratic temperature fluctuations can wreak havoc on the garden and affect plant hardiness. Some common challenges of this climate include the following:

• Generally poor soils: The dirt in this climate is usually stony, sandy, or highly alkaline clay. Humus content is very low. (See Chapter 3 in Book I for more information about soils.)
• Notoriously low humidity: The entire region is exceedingly dry.
• Unreliable snow cover: Because of the low humidity, snow usually evaporates before it has a chance to soak in.
• Very little rain: Lack of rain makes watering necessary, but water conservation usually limits the amount of watering allowed.

Xeriscape To Xanadu

Water is scarce and precious in arid regions. Coping with inevitable shortages has given rise to the xeriscape movement — combining good horticulture with water conservation to create flower gardens every bit as lush, full, and vibrant as those in more temperate climates. “Xeriscape” combines xeric (a dry habitat or a plant from such a place) with landscape to create xeriscape — literally, a dry landscape. Xeriscape is a system, not a style. A xeriscape can be as formal as Versailles or as casual as a cottage garden. You can’t drive up and down the street and pick out the xeriscapes; only the water bill tells the story.  ....read more