Get in the Zone
Hardiness zones in the US are determined by the USDA, based on data from 12-year cycles to determine the average low temperatures as well as extremes of cold. For many years, Cambridge, just north of the Twin Cities, was the dividing line between Zone 4 and Zone 3. In late 2002, the USDA published a draft revision that puts the divide further north, at about Detroit Lakes.
This means that the Twin Cities is in the middle of Zone 4, and we should feel comfortable planting all Zone 4 plants. Western Massachusetts is also Zone 4. We know, however, that Minnesota can have far lower temperatures than the average, even though the extreme lows are becoming fewer. We also do not have the reliable snow cover of Massachusetts, so Winter protection is a good idea for many plants that will not tolerate the occasional -30°.
So why does Bachman’s offer quite a few Zone 5 plants? Because many gardeners are successful with them. Usually this is because of several salient facts:
1. Protection from winter winds and sun
Winter wind and sun can dry out even tough plants. Out of wind and sun, many plants will survive and thrive. Away from the sun, thaw/freeze extremes are avoided.
2. Very good drainage coupled with humus-rich soil
The crown of many plants is easily damaged by ice or standing water, so good soil drainage is essential. Most plants cannot have their roots in water or ice for very long, if at all.
3. Plants are grown ‘lean’, with little artificial fertilizer
Too much fertilizer, especially if rich in nitrogen, develops soft growth that is easily damaged in cold weather. Plants that are kept stocky and tough are more reliable.
4. Microclimates are used well
As with many skills, good gardening is most of all paying attention to your space. Learn which areas are last to thaw and first to collect snow, which are first to melt, first to drain away after a storm. For many tender plants, reliable snow cover is the best insulation for surviving severe cold as well as the Spring freeze/thaw cycles. Even a warm spot will get below zero on a cold night. Early-blooming trees, such as Apricots, do best in the coolest area so they break bud later.
5. Appropriate pH
Altering soil pH is a long and slow process. Start with a good soil test. Almost always, adding compost is a good idea (up to 50% of volume); this makes for good drainage as well as lively, healthy soil. Use any organic material that is even slightly acid. It is very seldom the case that our soils are acid – usually they are very alkaline. Acid peat moss, pine needles or bark, uncomposted sorrel, cottonseed meal, cider press pulp, and other substances with a low pH will help. Do not try to speed the process with aluminum sulfate – you may kill your soil with heavy metals.
6. Light, fluffy winter mulch
Winter mulch must be light and not pack down in order to be effective. Excelsior, straw, Canary grass or long pine needle mulch will stay airy the longest. For very tender plants, a cylinder of chicken wire filled with loose mulch and wrapped with floating row cover, such as ReMay, may be needed to get them through hard weather.
Study the requirements given for the plant. If you cannot meet those needs, choose a different plant. Temperature stress is enough without adding to it the wrong soil or bad drainage or an exposed site. If your garden has just the right situations, you may be able to grow Zone 5 plants. Please understand that they will need more care than Zone 3 or 4 plants, and that you may be disappointed if you cannot provide the right situation for them to thrive.
For Additional Information on Zone 5
Protecting Trees & Shrubs in Winter
Mulches & Mulching
Soil Test Kits
© Bachman's Inc, 2004 Jackie Alfonso, Horticulturist