Using Hardiness Zones to Aid in Gardening

Every year at the height of winter, seed companies cannily send out catalogs illustrated with magnificent photos of the gorgeous fruits and vegetables you could potentially grow in your garden. Fired up with enthusiasm through the cold dark months of snow, many novice gardeners become convinced they can grow anything, such as peanuts in Alaska or olives in Idaho.

But the reality is different plants have different needs when it comes to how long they take to grow to maturity. We found this out the hard way when we moved from southwest Oregon (with its long growing season) to the North Idaho panhandle, a couple hours from the Canadian border.

For the first time, we learned how a short growing season can impact what plants we could grow in our garden. After getting caught numerous times with late-May frosts and early September snow, we realized we had to restrict our gardening ambitions to those plants with a growing season of 90 days or less. Once we understood this concept, we had far better success with our gardening efforts.

One critical factor when selecting what plants to grow is your particular plant hardiness zone. Broadly determined by zip code, these agricultural zones are based on the average annual minimum winter temperature, as well as length of growing season (usually determined by average date of first frost) for any particular area. The zones are divided into thirteen 10-degree (Fahrenheit) zones, and further subdivided into (a) and (b) zones. The lower the number, the colder the climate. Hardiness zones are a roughly useful way to determine which types of crops will succeed in your area. Most seed companies list hardiness zones with their products.

There are many hardiness zone maps and calculators available online. The U.S. Department of Agriculture has a searchable feature based on zip code, which divides most of North America into zones based strictly on winter lows. More detailed calculators will factor in latitude, elevation, ocean influence, continental air influence, and terrain (mountains and valleys). Additionally, it’s helpful to keep in mind any microclimates within these hardiness zones. North-facing slopes have a different microclimate than south-facing slopes.

For example, we live in an area in which temperatures can drop to -15F to -20F for brief periods in the winter. Nor is it unusual to get our first frost around Sept. 15. This puts us in Zone 5a. If we tried growing plants that require, say, Zone 7 or Zone 8 conditions, we would not succeed.

Fortunately, through the wonders of modern agriculture, there are endless varieties of fruits and vegetables (both hybrid and open-pollinated) suitable to every hardiness zone in America, from the warmest to the coldest. Once we learned what we could and could not do within the boundaries of our particular climate, we were able to establish a highly productive and successful garden.

Think of hardiness zones as a “cheat code” for your gardening ambitions. With one easy-peasy number, you’ll know at a glance whether the plants shown in your beautifully illustrated seed catalogs have a chance of succeeding in your own garden. If they do – well, happy gardening!