The 411 on Plant Hardiness Zones
It would be grand if garden centers only sold plants that are perfectly suited for their part of the country but that would happen only in an ideal world! However, as new gardeners get some dirt under their fingernails they learn that there are ways to push the boundaries and grow plants that were once considered off limits for their geographic region. But, in order to break or bend the rules, you first have to know and understand them.
The Rule of the Hardiness Zone: Plants have a zone, or a geographical area in which they can naturally survive. The hardiness zone of a plant indicates the average low winter temperature a plant can tolerate. As you move from zone to zone, the average cold temperate varies by 10 degrees. The lower the zone hardiness number of a plant, the colder winter temperatures it can withstand. By simply marrying the zone in which you garden with the hardiness zone assigned to a plant you will choose plants that will naturally survive your gardens’ coldest winter temperatures.
How to Figure Out Your Hardiness Zone: If you live in the United States, consult the USDA Hardiness Zone Map to determine your appropriate plant hardiness zone. You can even search by your zip code at http://planthardiness.ars.usda.gov/PHZMWeb/
If you reside in Canada, consult the Government of Canada, Natural Resources Canada website at http://www.planthardiness.gc.ca/
Bending the Rules: Just because a plant has a high hardiness zone number indicating it would not survive your garden’s winters doesn’t mean the plant is off limits. Lantana, for example, is a hardy perennial in the south but in the north, we treat it like an annual. Lantana cannot survive our winter temperatures, but it does just fine in our summers. So just like other annuals, you can enjoy Lantana all growing season long up until frost.
Breaking the Rules: Let’s say your garden is in zone 5, chances are you have micro-climates in your yard; areas that may stay a bit warmer or get colder depending on wind breaks, proximity to the house, sun exposure and natural topography. In some cases plants can be coaxed to survive in a zone that is one or maybe even two zones away from their natural setting. This is a fun and exciting way to challenge yourself as a gardener and expand your plant repertoire. However, if you are new to gardening and are unknowingly selecting plants that are not suited for your hardiness zone and they are no surviving from year to year, it can be frustrating and discouraging.
The best advice for new gardeners is to start with plants that love your hardiness zone. The selection that is available to you is impressive, no matter where you garden. Then, as you get a better feel for the nuances of your garden space, experiment and live a little. Just go in to it with your eyes wide open knowing that the percentage is not necessarily in your favor and that eventually you could lose plants not hardy to your zone. You must always remember in gardening that you are #1 dealing with a living thing and #2 we are at the mercy of Mother Nature who can change her mind on a whim.
Images courtesy of the USDA