What’s your “zone” – and does it really matter?

Published 9:43 am Wednesday, November 23, 2022

Every day I get emails from gardeners and field questions on the Mississippi Gardening Facebook page about growing various plants, in which the writers mentions their USDA plant hardiness zone. Which to me is has little to do with reality of gardening in the Magnolia State.

Here I go again, seemingly disputing the production-efficiency dogma preached by my hortiholic peers. But, as you and I know, and Aunt Mamie, who is a pretty darn good gardener in spite of never having taken Master Gardener classes, there are some things we horticulturists say that are technically correct but aren’t strict requirements for average home gardening success.

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It’s like me adding at the end of all my emails that I’m a Gemini; my birthday month doesn’t account for my upbringing, attitude, where I live, which way I vote, or whether I prefer wine or a stout ale. Those are conversational starting points, not insights into my overall character.

What these earnest gardeners are basically are telling me is simply whether it freezes in the winter. Yet, except for summer annuals and tropical plants that can’t tolerate cold weather for long, the actual low mark doesn’t matter all that much – a freeze is a freeze, whether it hits single digits, hovers in the teens for a few days, or just dips temporarily into the upper 20s along the coast.

I mean, England, which is on the same latitude as Nova Scotia, should be super cold most of the winter, but because it is surrounded by warm Gulf Stream water it is in the same USDA zone 8 as most of Mississippi. To repeat: Mississippi and England are in the same zone. Same with Seattle. All three places rarely get down into the teens, rarely has ice.

Actually, coastal England, Ireland, and even Scotland is the same zone 9 as our coastal counties, yet they grow stuff we can’t.

Regardless of how zone charts tell us that David Austin roses should grow in Mississippi, doesn’t make them so. They have a tough time dealing with our heavy rains and hot, humid summer nights.

Which is my point here. No matter what the charts say, old-hand gardeners know that plants are limited by more than cold weather. Some, like banana, amaryllis, and citrus can take a little freeze but not prolonged or really deep freezes, but for the vast majority of good garden plants in Mississippi it’s all about the same.

This is because there are other important factors that affect plant growth, including summer heat (especially at night), heavy rains, long sunny but dry spells even in the winter, sun or shade, soil type, nearby tree roots, and how everything is changed by how we plant, water, and fertilize, plus insects and diseases. Throw in microclimates that change the surroundings, like how a normally hardy yard plant may not survive in a mall parking lot.

What we need, in my opinion, is a Mid/Lower/Coastal South Map that overlays average cold winter temperatures with dramatic midweek ups and downs, plus our average first and frost dates, plus hot, muggy summer nights that are what actually do in a lot of plants, our too-wet winters and too-dry summers, miserable dirt, incredible pest pressures, and busy gardeners’ schedules.

No matter if your zone is 7, 8, or 9 (forget that worthless “a” and “b” thing), it only matters to a few plants along the coast. And anywhere gardeners protect borderline plants, it all becomes moot.

Where it freezes, zones, like zodiac, are not good indicators of success.