U. S. planting zones are based on the weather history of any given area. The question “what planting zone am I in?” is one of the most asked by beginning gardeners. Knowing your planting zone is the first place to start on your journey to becoming a successful gardener.
Hardiness zones remove some of the confusion experienced by gardeners when trying to determine whether a plant will endure the winter cold or summer heat in their area. There’s also the question of the number of days in your growing season, which influences what you can or can’t expect to produce in your garden. Knowing the answer to what planting zone am I in can even help save you time and money as you won’t purchase plants which won’t thrive in your zone.
When You See “Zones 3-7” on a Plant Label, What Does it Mean?
These numbers represent the hardiness zone developed by Harvard’s Arnold Arboretum, which put together guidelines to give us a notion of how plants would survive the temperatures in a particular region. The 1990 hardiness zone map was said to be created according to historical weather patterns. The U.S. has 13 zones in all and nearly all plants are assigned a hardiness zone.
To find your zone, visit the USDA’s website and click on your state or enter your zip code. You’ll notice each zone is broken up into “a” and “b.” The “a” portion of the zone typically has a winter which is five degrees colder than the “b” portion.
It’s interesting to me, being farther north doesn’t necessarily mean colder temperatures. For example Portland, OR; Tallahassee, FL; and London, England are considered to be Zone 8, even though they are at 30-, 45- and 51-degrees latitude. There’s a simple reason for this. The jet stream and coastal winds modulate the weather in London and Portland making them similar to Tallahassee. Since their “asphalt jungles” retain heat, big metropolitan areas may also be somewhat warmer.
This is much like the effect experienced by an off-grid homesteader I know who lives a few miles down the road. Their homestead is at 3200 feet above sea level up on a mountain. Although he has snow longer than the valley below, he can produce a nice crop of corn because he has a longer growing season. My friends in the valley have to use cold frame gardening to help prolong their season. I was shocked too! The reason is the rising heat from the valley floor late in the fall and early winter which creates a longer season for him. Who knew?
When You See “Zones 3-7 / 4-6” on a Plant Label, What Does it Mean?
We now understand what the first set of numbers on a plant label means, but what about the second set? These cover heat zones which can be endured by the plant based on how hot it gets in summer in each zone. The heat zone map is broken up into 12 zones and is founded on high temperatures. The lower the number, the cooler it is in summer. For example, Portland, OR, is in Heat Zone 4. They experience between 30 to 15 days each year with temperatures above 86 degrees. Most of Texas, however, is in Heat Zone 9 where they experience between 121 to 150 days of temperatures 86+ degrees. The American Horticultural Society developed the heat zone map.
Beyond Planting and Heat Zones
Even though hardiness and heat zones are incredibly helpful, they don’t tell the complete story. You’ll find many other weather factors play a role in how well a plant will grow for you, including wind, rain and humidity. These maps were compiled on average temperatures, so they can’t account for unusual weather patterns. We’ve had an increase in what I would call unusual weather especially this year (2016).
Also, zone maps don’t tell us about micro-climates, which are little regions within an area where weather is distinctly different from the rest of the zone. An excellent example of a micro-climate is a mountain. It’s not uncommon for those of us who live in the mountains, especially 3000 feet or more, to experience snowfall even up until July when others below 2500 feet don’t. Even though we’re in the same zones, elevated micro-climates have to have their own considerations.
Wind-sheltered pockets on the south side of a mountain beside a mountain stream create a dramatic difference in climate. Banana trees can sometimes be planted outside farther north than the traditional zone, if they are planted close to the south-facing side of a structure. Several micro-climates can exist in one location.
You may be like me and are wondering if a micro-climate is affecting your plants and homestead? To know this, you should take your own temperature readings around your homestead. I would document them over a whole growing season to determine a pattern. If you keep losing crops or the yields are not up to snuff with some of your plants, you may have a tiny micro-climate affecting their ability to produce.
What About Sunset Zones?
Sunset magazine created its weather zone maps years before the USDA. Sunset zones are regarded as being more exact than USDA hardiness zones. These zones take into consideration many more factors which affect crop production than the USDA. They’re expounded and recorded on in the Sunset Western Garden Book.
Considering Frost Dates
Understanding what planting zone am I in according to your zone’s frost dates is crucial. The last frost date lets you know when it should be safe to put certain varieties in the ground. The first frost date allows you to know when you may need to bring any non-hardy plants inside for the cold winter months or harvest the crop.
These dates can help you plan (and I love my garden journal for this) your gardening tasks like when to add chicken manure compost. They’re only guidelines, remember there are micro-climates and weather patterns not predictable when establishing guidelines. The other factors we’ve discussed also affect the best time for everything gardening. So keep these dates in mind as guidelines, especially when buying new plants in the spring, planning your garden strategy, implementing gardening tips, or putting your garden to bed for the winter.
You may want to bookmark these resources until you know what zones and other basic factors affect you and your garden. It won’t take you long to remember. The next time someone says, “If you are in Zone 8 I wouldn’t try to plant that,” you’ll sound like an expert when you reply, “Intriguing information. I am in Zone 8, but my valley micro-climate enables me to grow it and you should see the nice produce I get.”
Knowing what planting zone you’re in is important information. Do you know the answer? Let us know in the comments below.
Safe and Happy Journey,
Rhonda and The Pack