Old gardening humor describes the best way to tell whether a newly emerging spring plant is a weed or a valuable perennial. Tug on it.

If it pulls out easily, it was a valuable perennial. If it remains stubbornly in place, it's a weed.

As important as recognizing weeds from perennials is separating adapted trees and shrubs from non-adapted.

Everyone wants their trees and shrubs to survive and flourish, especially those we've just bought and planted. Unfortunately, some plants sold in the Upper Midwest are not winter-hardy or adapted to our conditions.

Garden centers might contain three types of trees and shrubs: those fully winter-hardy and adapted to our growing conditions, borderline types that might do well in protected sites with special care, and lastly, varieties that are non-hardy, non-adapted, and probably shouldn't be sold because they usually end in failure.

When shopping for trees and shrubs, how do you know what's what? Non-hardy material is often displayed side-by-side with adapted types, with little to distinguish between the two.

Here are tips for separating well-adapted from non-adapted:

• Locally owned garden centers have built their businesses on selling trees and shrubs suited to our region. Most of their stock is winter-hardy, but they might also offer material that's less widely adapted but still successful in the proper spot with proper care. These garden centers can be shopped with confidence and offer the widest selection of suitable plants.

• Garden centers of national chain stores have difficulty supplying only adapted material. Store purchasing agents are probably ordering for large chunks of the country, and what's adapted for Omaha doesn't always play well in Fargo. When shopping for trees and shrubs at national chains, it's important to investigate types closely before buying. Adapted material is often intermixed with non-hardy types.

• Examine tags closely, because they contain valuable information if you know what to look for.

• Check tags for the USDA hardiness zone. The northern third of North Dakota and Minnesota are in zone 3, meaning plants must survive winter temperatures as low as minus 30 to minus 40 degree. The lower two-thirds of the region are in zone 4a, with winter temperatures dropping to minus 25 to minus 30 degrees. Unfortunately, many plant tags just indicate zone 4 without differentiating between the hardy zone 4a and the borderline hardy zone 4b. In summary, much of the region can rely on plants designated zones 3,2 and 1. Plants termed zone 4 should be further investigated, because some are borderline hardy and some are fine.

• Instead of listing hardiness zones, some tags indicate temperatures like "hardy to minus 20 F." To be reliable, trees and shrubs must survive to minus 25 to minus 30 degrees F. Minus 20 is borderline in hardiness.

• Look for the botanical name genus and species in the tag's fine print. The name unlocks a world of information. For example, Hydrangea macrophylla varieties like Endless Summer require very special care for survival. Instead, check for varieties of Hydrangea arborescens and Hydrangea paniculata because they're well-adapted and recommended for widespread planting.

• Be especially cautious of the following commonly sold items: Dwarf Alberta Spruce, rhododendrons and azaleas other than PJM Rhododendron and the Lights series of azalea, blueberries except in Minnesota acid soil, and the Knockout, Easy Elegance and Flower Carpet series of roses, which are better adapted to zone 5. Instead choose Canadian hardy varieties of roses.

Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler's Greenhouse in Fargo. Readers can reach him at forumgrowingtogether@hotmail.com.

He also blogs at " target="_blank">growingtogether.areavoices.com.