MANHATTAN, Kan. – The past year’s weather was clear proof plants have to be tough to thrive in Kansas.

Gardeners would do well to remember that, as they replace or add to home plantings this spring. Forecasters are calling for a long-time return to extreme weather.

Winter’s cold and April’s sudden freeze showed why Kansas is the midpoint of USDA’s cold hardiness zones for the 48 contiguous states, said Ward Upham, horticulturist at Kansas State University.

USDA’s map indicates Kansas landscapes must be able to survive:

* 0 to -5 F in small pockets of southwest and south central counties (zone 6b).

* Minus-15 to -20 F in spots across the northern tier (zone 5a).

"USDA revised its map in 1990 because we were losing types of landscape plants that survived well from the 1940s through the 1960s. Unfortunately, Kansas’ weather changed even more over the past decade," said Upham, who is K-State Research and Extension’s specialist in fast-changing plant problems.

The U.S. National Arboretum – which maintains and distributes USDA’s map – reports that all of North America’s temperature and moisture ranges were wider over the last decade than in 1940-70.

"Weather watchers say this represents the beginning of a return to more ‘normal’ patterns," Upham said. "Given Kansas’ weather history, that suggests we can look for all kinds of extremes.

"Besides, USDA’s zone numbers are no more than averages – averages of wintertime temperatures that were much milder and colder. That’s why people who don’t have time to worry about protecting landscape plants should consider ones that are rated for even colder living conditions – zones 3 or 4."

Of course, surviving cold isn’t all Kansas plants have to do. Homeowners got clear evidence of that last summer, watching lawns turn wheat-hued and fragile ornamentals lose leaves, look burned and/or die.

The American Horticulture Society recognized this challenge nationwide several years ago by releasing a weather history-based U.S. heat zone map. The AHS is encouraging wholesalers and retailers to use its divisions alongside USDA’s zone numbers, in describing plants for sale. The map shows 12 zones, determined by the average number of days each year that a location’s temperatures are 85 F or higher.

"That temperature is the point at which proteins in plants start to come apart," Upham said. "As a result, photosynthesis slows down and the plant makes less food every day. Plus, plant respiration speeds up, burning up that food and then the plant’s food reserves.

"Worst case is when daytime temperatures are above 95 degrees and nighttime temperatures are hot, as well. Having its proteins denatured by heat sends a plant into a slow, lingering decline. If and when all its food supplies are gone, the plant dies."

Most of the industry has yet to adopt the AHS map, so selecting plants that withstand Kansas’ summertime heat can require homework.

"I’d certainly ask nursery personnel about plants’ heat tolerance. I’d talk about landscape possibilities with neighbors and my county Extension agent," Upham said. "I’d also look for plants’ ability to withstand heat stress when reading catalog descriptions or looking in gardening books – although what they call tolerant may apply in Massachusetts or Oregon, but not Kansas ... at least not without afternoon shade.

"A useful guide for both cold and heat tolerance, however, is simply to drive around where you live. Notice the large trees and shrubs – the ones that have withstood the test of time. Then walk through neighborhoods with landscapes you admire and take a closer look at which perennials seem to be standards, doing well in yard after yard."

One reason the industry is being slow to adopt the AHS heat map is that it doesn’t reflect average moisture -- which can play a big part in how well plants perform in different areas within the same zone.

In Kansas alone, warm days that are moist tend to foster plant diseases. They may support unusually heavy insect infestations, Upham said.

In summer and winter alike, however, "normal" weather can rapidly take Kansas’ natural moisture supplies from sopping wet to near-desert levels.

"I tend to recommend ornamentals that have some drought hardiness," the horticulturist said. "Water isn’t one of the state’s most abundant resources, in spite of the occasional flood. Rules for limiting water use are already business-as-usual for some towns in summer. Those kinds of limits will probably spread, as our population grows and we have more cars to wash, pools to fill and lawns to water.

"Besides, having to irrigate frequently can be a big investment of time and money. Even then, it may not be enough to save a water-loving plant, facing extreme summertime temperatures."

A newer, but growing concern in many suburban areas is finding plants deer and rabbits don’t like.

"Fortunately, those kinds of plant-eating wildlife are grazers. They don’t tend to stay in one spot and eat things down to the ground in one night," he said. "Unfortunately, they also are creatures of habit. Once they find a good grazing spot, they tend to come back again and again until winter.

"Barring wildlife from a landscape is a bigger challenge than most people want to tackle. So, their sensible course is to choose plantings that are pretty, but aren’t particularly attractive to wildlife."

Some nurseries and catalogs are providing wildlife-related information, Upham said. But, it’s mostly the result of folklore experience and still needs more research to back it up.

"Wildlife can take you into the area of trial and error," he said. "If they eat something, then you buy something different. If they don’t eat something, you buy more of it.

"To a degree, however, all of landscaping is just that – trial and error. Each property – each combination of house shape, trees, angle of light, wind direction, sun exposure, shade, soil and moisture – has microclimates within it. Things that will grow well in one part of the yard may fail in another. Things that your neighbor produces like weeds may refuse to grow where you live."

Upham added that in general, however, the following can help in planning for those mini-climates:

* Plant frost-vulnerable ornamentals on the north of the house, where they’ll be the last to warm up in spring. The longer they take to break winter dormancy, the less likely they’ll be to get caught by a late freeze.

* Assume that any plant you don’t see thriving all over town in all kinds of sites may very well need afternoon shade in the summer.

* Plant fragile-limbed plants on the side of the house that’s away from prevailing winds. Or group them with thick evergreen shrubs or next to a fence that can act as a windbreak.

* Mulch, to preserve water and even out temperature extremes in summer and winter.