Zone 6 – What Is It?
The term “zone” refers to the range of temperatures from 20°F (–7°C) to 60°F (15°C). The lower end of this temperature range is known as the “temperate zone”, which extends from 30°F (-1 °C) at sea level up through 40°F (4 °C), with some areas reaching 50°F (10 °C). The upper end of this range is known as the “tropical zone”. Areas in the tropics are hot and humid, while those in the arctic circle experience cold winters. The tropical zone covers most of the earth’s surface, but it does not extend far into space. Most of the world lies within its temperate or tropical zones.
In general, plants grown in these climates require little care other than regular watering and fertilizing. However, certain species thrive better in one climate over another; others have adapted to their particular environment so well that they do not need any special attention at all.
What Is Zone 6?
The USDA (United States Department of Agriculture) has divided the country into “plant zones.” Each zone is identified by the average annual minimum temperature in that area. The lower the zone number, the warmer the climate. There are eleven zones in all, ranging from Zone 1 (above 13°C or 55°F) to Zone 11 (below –50°C or –58°F). The greatest differences in plant types occur between Zones 1 and 2, and Zones 8 and 9. These zones represent differences of at least 9°C (16°F) in average temperature.
The best method of determining your plant zone is to look it up on the USDA Plant Hardiness Zone Map, which is updated every 10 years. It contains separate maps for the lower and upper continental U.S. and Alaska.
If you can’t find your city, you can search for it using the USDA’s database of American locations. Just type in the city name or ZIP code to get its Plant Hardiness Zone.
You can also narrow down your plant zone by looking up your average annual high and low temperatures. On the USDA Plant Hardiness Zone Map, high temperatures are listed on top of the map, while the low temperatures are listed on the bottom. For example, if your average high is 23°C (73°F), you would look at the 23°C column for the upper continental U.S.
The annual average high and low temperature numbers used to identify each zone are based on data from the years 1960 to 1990. Because the weather in recent years has tended to be “weird”, it is possible that your zone may have shifted somewhat since then.
Many plants require a specific USDA Hardiness Zone in which to grow successfully. The hardiness zone indicates what the lowest temperature the plant can endure is and still survive. While some plants can be grown in warmer zones than the one you live in, most should be grown in a zone lower than yours.
Before planting a zone warmer than yours, check to see if the plant is suited to your area by looking at its USDA information. The easiest way to find that is to go to the page for that plant and look for the letters “HD”. The number that follows (ex: 20) refers to the plant’s minimum winter hardiness zone.
Zones can be confusing because they are only numbered every five degrees. For example, Athens, Georgia (Zone 7b) can have winter temperatures ranging from -5°F to 60°F. But because the zone numbers jump from 6 to 8 at the 6.5° mark, it’s known as a Zone 7b, not a Zone 7.5.
The same concept applies for zones that are even numbers (4, 6, 8, etc).
When moving plants from a colder zone to a warmer zone, be aware that they may require special care until they’ve had a chance to acclimate.
What if I don’t see the letters “HD” anywhere on the plant page?
If you can’t find any reference to the plant’s growing zone, try looking up the genus (a fancy word for the “type” of plant) on Google. For example, if you’re looking up foxglove, search “Digitalis” instead.
What if I still can’t find it?
If you’ve looked up the genus and still can’t find any reference to a growing zone, that probably means the plant is native to your area or naturalized there (i.e. it lives there now even though it isn’t native). You can probably assume it will grow fine in your climate.
Cold Tolerant Plants
These plants are tolerant of cold temperatures.
Blood Root (Requires Nightshade)
Blazing Star/Lance Leaf Tuckeroo (Aren’t these the same thing?
Cactii (Most Cactii are cold tolerant. But you still shouldn’t let the temperature drop below freezing.)
Cast Iron Plant (As name implies, this one can stand a lot of abuse. Perfect for a pot on a porch.)
Cat’s Whiskers (Don’t use if you have diabetic pets. They might eat it and go into a coma. Seriously.)
Ceramic Plant (Another good potted plant for a porch.)
Chinese Evergreen (This is a common houseplant, so you may already have it.)
Cliffbrake (Another common one)
Corn Plant (aka MSM, the plant that’s not a plant)
Crab’s Eye (aka Stonecrop, very pretty if you can persuade them to bloom. Do NOT trim off the flowers!)
Dumb Cane (aka Dieffenbachia. Don’t let the kids suck on this one or it’ll make them choke.
Sources & references used in this article:
Wyman’s gardening encyclopedia by AM Armitage – 2011 – Timber Press
Gardening in the Lower Midwest: A Practical Guide for the New Zones 5 and 6 by D Wyman – 1986 – books.google.com
Herbaceous perennial plants: A treatise on their identification, culture, and garden attributes by D Heilenman – 1994 – books.google.com
Plant growth factors: temperature by AM Armitage – 2008 – books.google.com
Fitting models predicting dates of flowering of temperate‐zone trees using simulated annealing by D Whiting, M Roll, L Vickerman – Gardening series. Colorado …, 2003 – mountainscholar.org