What Planting Zones Information Tells You and Doesn’t Tell You
Blue has been described as being one of the warmest of colors, but as far as planting zones are concerned nearly the opposite is true. Color maps illustrating these zones usually indicate the colder areas in blue. The only areas colder than blue are those that are sometimes shown in white, like the color of Arctic snow, although very cold areas are also shown in red, which does not seem to make sense since we normally associated red with heat.
Hardiness Zones – More to the Point
These zones are sometimes referred to as hardiness zones. This is because the key factor in defining each zone is the minimum temperature a plant is expected to be exposed to. Zones are usually defined based on the average minimum temperature that is likely to be experienced in that location. Consequently, zones don’t always apply to annuals, which will grow even in cooler zones as long as the growing season is long enough for them to produce flowers or fruit.
Since these zones are defined in terms of hardiness or average minimum low temperatures, additional information is sometimes needed to determine how well a plant will grow in a given zone, or if it will grow there at all. Some zones, particularly those located inland, can experience extremes in temperatures. These extremes are less likely to be felt in coastal areas. There are many plants that can tolerate fairly cold temperatures but will wilt when exposed to high temperatures for a long duration.
One also needs to be aware of the times of first and last frost. Some flowers and vegetables that will do extremely well in either warmer or cool climates cannot tolerate the slightest bit of frost. Others can, but they will die back with the coming of the first hard frost. Planting zones do not given an indication of humidity, a condition that is just as critical as temperature to some plants.
Where the Different Planting Zones Are Located
Look for tables or maps titled USDA Hardiness Zones. USDA stands for the United States Department of Agriculture, the governmental department responsible for defining the zones and determining their locations and coverage. Zones tend to be pictured as bands going from west to east across the United States, with the higher numbered zones located in the southern states and the lower numbered or cooler zones appearing across the northern tear of states. The coldest zones, USDA Zones 3 and 4 are located in the northern tier of states stretching from Montana into upper New England. These two zones also extend southward as along the Rocky Mountains, reaching as far south as the Colorado-New Mexico border.
USDA Zones 5 and 6 run right through the midsection of the country, going from the interiors sections of Washington and Oregon, into Idaho and Nevada, and extending from eastern Colorado to the Atlantic coast. Zones 7 and 8 are located in western Washington, western Oregon, and through the southern tier of states all the way to the Atlantic. Much of southern California, Arizona, a strip along the Gulf Coast, and most of Florida is in Zone 9. Zone 10 which is for all practical purposes a tropical zone, is reserved for the southern tip of Florida. Some states, like Idaho and Colorado, host several different zones.
Zip Codes Are Useful
Over the years, planting zones have become more and more precisely defined. Still, a large field suitable for planting a number of different crops can contain hollows or frost pockets where some of those crops will not grow well if at all. Elevation can also be a factor. You may live in Zone 8, which essentially covers your entire state, but if mountains run through the state, those living in those mountains could find themselves in Zone 5, or even in Zone 4. With the advent of the zip code it has become easier for retailers to tell their customers which plants are suitable for their location and which may not be. It’s now possible to determine to a fair degree of accuracy which zone a particular zip code lies in.
Additional Information Is Sometimes Needed
Those who plant crops or grow vegetable every year sometimes need additional information besides the number of the zone they live if they’re going to get the best results. Knowing when to prune your plants or when to prune roses is also very important to keep plants and crops healthy. The length of the growing season is one factor. Your summer temperatures may be fine for growing watermelon, but if you live in an area where summer is short and spring and fall are longer and cooler, watermelon or any other melon may not do well. Along with the knowing the average duration of the growing season, one also needs to know either the times of the first and last frosts, or the approximate date when the soil will warm up to a certain temperature. Planting zone information does not always provide all the information one needs. Sometimes, planting conditions can vary considerably from locality to locality, even within the same zip code. Your county Extension Service, which is normally affiliated with either the Department of Agriculture or a nearby college or university, can usually provide you with the detailed information you might need.