You’ll often see references made to garden zones and micro-climates in gardening articles. Zones refer to arbitrary divisions (based loosely on research and garden reports) of North America into 10 areas. The lower the number, the colder the “zone” and the higher – the warmer the zone. The difference between zones is 10 F. warmer (or colder) winter temperature.
I debated about putting a rough zone map here as a graphic, but decided that you would get more “real” information from the original USDA map.
The link below is “hypertexted” and this allows you to go to this site – and click on your own area bringing you right to your own neighborhood.
The click zooms you into a closer view and you can see the individual micro-climate zones in your area.
Click here for the USDA zone map
Gardening zones are interesting guidelines for plants but generally speaking – they are only guidelines.
Plant breeders suggest this plant or that plant is rated for zone XX. Well, sometimes that’s true and sometimes it isn’t. The nursery wants to sell more plants so it “broadens” the zone a little. Nursery X will say zone 4 and nursery Y will say zone 5.
Zones are guidelines.
My rule of thumb is that I’ll grow plants that are rated colder than my zone with no problem and I’ll usually succeed with plants that are one zone warmer than my garden zone.
- So if I live in a zone 4 – I’ll usually succeed with zone 5 rated plants.
- I’ll sometimes succeed with zone 6 plants and I’ll maybe once in a dream succeed with zone 7 plants.
- But those zone 3 plants are rock solid in my garden.
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.
Get The Sunlight Right
Make sure the sunlight requirements are met.
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.
Micro-climates.
- 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.
Bottom Line
Take nursery tags and advice on the gardening zone map with a grain of salt and consider them broad guidelines for gardening success.