If you felt a sudden change in atmospheric pressure around Jan. 25, it was Central Oregon’s long-time gardeners gasping at the news release of the newly revised U.S. Department of Agriculture Cold-Hardiness Zones.

The USDA Cold-Hardiness map is the Holy Grail of gardeners. Most of us have moved here from other areas and as true gardeners, we checked which zone Bend was in accordance with the USDA map. That was what helped guide our plant decisions until we learned lessons the hard way and really understood Central Oregon weather.

As defined by Oregon State University’s “Central Oregon Climate and how it relates to gardening,” revised July 2009 and authored by Amy Jo Detweiler, a Horticulture faculty member, “the term hardiness refers to the ability of a plant to withstand an average minimum temperature.”

Prior to the revised map, Central Oregon was classified in Zone 5; minus 20 degrees Fahrenheit to minus 10 degrees. The new map puts Bend in Zone 6b; minus 5 degrees Fahrenheit to 0 degrees. Included in the 6b zone are Madras, Prineville and Redmond. As a point of reference, this puts these communities in the same zone (6-7) that Portland was in on the previous map.

La Pine, Sisters and Sunriver have been upgraded to Zone 6a, which is minus 10 degrees Fahrenheit to minus 5 degrees.

The Sunset Western Garden Book is a popular reference book that also features a series of climate zone maps. Its information is climate driven, not hardiness driven. Its zone numbers would not be used on plant tags or in horticultural information other than publications from Sunset Publishing.

This is the first revision to the USDA map since 1990. The new map uses weather data collected from 1976 to 2005. You can view and download the map at http://planthardiness.ars.usda.gov/PHZMWeb. The site is searchable by ZIP code. Expert meteorologists seem to agree that the new version shows warmer zones migrating northeast.

Catherine Woteki, an undersecretary of the Department of Agriculture, cautioned against reading too much into the changes. “We do not think the plant hardiness zone methodology is appropriate for making comments on climate change,” she said.

I can understand how gardeners and professionals living in more stable climates than ours could be excited about the changes.

Woodrow Nelson, director of marketing communications for the Arbor Day Foundation, relates that members have been noticing climate changes for years and have been successfully growing new kinds of trees in places they wouldn’t grow before.

My mind boggles at the print changes that need to be made for next year. Think of all the catalogs, seed packets, manuals, books, fact sheets and the informative handouts that are so freely given at gardening events. Maybe all the reissuing of materials will be the economic turnaround we are all looking for.

Local changes?

Now it’s time to get practical and realistic. In other words, how is all this going to apply to Central Oregon gardeners?

According to the OSU “Central Oregon Climate” publication, “Hardiness ratings or zones are intended to be used only as a guide, not as absolute for plant selection and survivability. Especially being the case, here in Central Oregon where we have several microclimates.”

Our new rating, which pushed us into a warmer zone, does not mean we have to change what we’re growing or that we can successfully grow the plants that do well on the west side of the state.

Many environmental factors contribute to the success of plant material. Wind, soil type, soil moisture, humidity, pollution, snow and winter sunshine can make or break success or failure of plant material. Add to all of those factors the untimely frosts that can sweep over the High Desert area.

All of these factors are different on the east side and the west side of the state and changing a zone number doesn’t necessarily mean we will have success.

Lack of snow (soil moisture) and strong desiccating winter winds are our worst enemies as may be evident when spring arrives and we can access any winter damage. Many gardeners this winter have carried buckets of water to protect fall planted perennials and other landscape materials. Our soil, unless it has been amended, does not hold moisture; so even in a normal winter with snow cover, the winds can dehydrate plant material.

When we moved to Central Oregon in 1978, my husband headed back to Alaska for a three-week work stint with the Stark Bro’s Nurseries catalog and a blank check tucked in his briefcase.

He chose a plethora of dwarf fruit trees, all precisely chosen for the Hardiness Zone 5, which we had researched. By the time the saplings arrived, the underground watering system was in place; all the bells and whistles were done according to the book. We dreamed of an orchard filled with peaches, pears, apples and pie cherries.

Marvin Young, the extension agent, somehow heard about the crazy Alaskans and drove up the long drive of our Tumalo farm for a look and a chat.

We received kudos for spacing, and planting but a mild warning that the sage rats would probably take an experimental bite out of the flexible underground watering system. Then Young really burst our bubble.

Young explained that Central Oregon weather, with its damaging unexpected frosts hitting the trees at critical bud and blossom stages, would likely kill off any fruit production. He was right on. Three years later — out of $500 worth of trees — we ended up with one pie cherry. Not one tree, but one cherry and, to add insult to injury, the birds had attacked that. The blooming orchard was enjoyed each year for probably three or four days before the frost hit and blackened the blossoms. We always hoped that the sage rats got a good bellyache from nibbling.

I am sure there are hundreds of similar stories in the area of forging ahead thinking we know what we are doing. We need to totally understand Central Oregon weather, and a change in a number doesn’t give me and many others I have talked to a great deal of confidence. You still need to know how gardening works here.

I’m happy for the gardeners in Boston who can start growing fig trees as reported and that camellias will now be moving north from New Orleans for plantings in North Carolina.

Experiment to your heart’s content; that is the joy of gardening. But don’t feel like a failure if the big-leafed semi-tropical plants grown in Portland end up being a disaster here.