When it comes to a gardening zone map and using it, there are a lot of myths out there. Here’s the practical deal on them.
They’re guidelines not rules
A garden zone is a rough guideline (and I do mean rough) for what will or won’t grow in your general area. (Get the picture – lots of qualifications here)
Things to Consider
There’s no single source for which plants grow in which zones. So you’re going to find different nurseries rank plants differently
The growing conditions dramatically influence the growing zone in your garden. Some parts of my garden are an entire zone warmer than other parts.
Nobody wants to talk about it but there was a fair amount
of controversy about the USDA gardening zone map setting zones and then changing the timeline
they’re calculated on to reflect a different set of data. Some folks say this was politically motivated
to “prove” global warming doesn’t exist.
Me? I’m Canadian and don’t really care what the politicians do – I think
the folks on the committee do their best and because I use the maps as rough
guidelines and not hard and fast rules, it’s “all good” for me.
How to Grow Plants Out of Your Gardening Zone
The trick here is to give plants exactly the conditions they want. You see, if you stress a plant, it might live within a area that’s right for it but because it’s stressed a bit, it won’t survive in colder areas.
Make sure the drainage is right. This is the number one problem with overwintering plants out of their gardening zone. Most of the time, the soil is too wet for the plant when you’re trying to push a plant to survive in a colder area.
Make sure the sunlight requirements are met for broadleaf plants. As a simple example, broadleaf plants (shrubby plants that hold their leaves all winter) do not want to be in the bright winter noon sun. The heat from the sun on the leaf warms up the leaf – the sweat cells on the underside of the leaf (stomata) open up and the leaf loses water. It can’t replace it because the ground is frozen so the leaf “burns” or browns. This happens quite frequently in early spring. So siting is critical for plants to grow slightly out of their zone.
Plants that are in the direct wind are going to have more stress on them than plants out of the wind.
Plants that are tucked up against a large thermal mass such as a rock wall will receive a degree or two of frost protection.
Plants that are planted next to heated basements will get several degrees of frost protection from heat leaking from the basement.
Plants on south facing slopes will start growing faster in the spring than those on north-facing slopes. This can be an advantage with hardy plants but a disadvantage if you have a plant that is frost tender and can be wrecked by a late frost.
Take nursery tags and advice on the gardening zone map with a grain of salt and consider them broad guidelines for gardening success.