Using USDA zone information

[evtubbergh]

Every time I look up a plant from anywhere else in the world but here, there is this USDA zone number so I have taken to checking the map to find out what minimum temperatures a plant can handle. So that is helpful but what I don't understand is why there should be more than one zone, or a range of zones.

Surely if there is a minimum temperature a plant can handle than that is it?

There is a post in here https://www.helpfulgardener.com/forum/vi ... p?p=275693 that really says what I was thinking about the usefulness of this information. I would prefer information on a website that give min and max temperatures, rainfall, general climate etc.

[webmaster]

You're right, there's more to a plant's ability to grow in an area than just the temperature. I was talking about this over the weekend with my brother in law, Scott. I referenced the concept of Terroir. Scott agreed, that certain plants simply do better under certain conditions that go beyond hardiness zone.

The soil type is important. The PH is important to certain plants. Elevation, rainfall the type of soil itself. In the concept of Terroir, wine grape growers noticed that certain kinds of soil and temperature variations impacted the taste and productivity of the grape vines. For example, a specific range of temperature variation was preferred. Which is why some of the best wines are grown in valleys, mountain sides, near a river or a miles from an ocean, where the cooling fog creeps in over mountains in the evening. The famed The Côtes du Rhône wine growing area is located among rivers in a valley, notably the Rhone River. I was told that the soil and temperature variations in Paso Robles were similar, which is why the Perrin family chose to purchase land there and grow vines in that area under the Tablas Creek label (good wine!).

[rainbowgardener]

Plants are usually listed with a range of zones where they will reliably grow, like hardy in zones 6 through 9. That means it can't tolerate minimum temperatures lower than what is found in zone 6. This plant needs some cold dormancy so won't do well in zones warmer than 9 where there wouldn't be enough cold winter for them. They should be OK in any of the zones in between.

There are certainly other factors influencing how well a given plant will do in a given region, but the USDA zone gives you no information about any of those. The reason a range of zones is given is because there is both a lower bound and an upper bound for how much winter plants need/ can tolerate.

[imafan26]

The zone maps are mostly concerned with cold tolerance, or in my case heat tolerance. But, you are right there are a lot more considerations like soil type, pH, elevation, water to consider.

The easiest way for me to tell if it is a plant I can grow is to look up its country of origin. If it is only grown in a very narrow range at specific elevations, I probably cannot grow it unless I can provide the microclimate.

If it is a cultivar that has be bred for a wider habit range, I might be able to.

For instance in Hawaii I can grow azaleas where I live but not rhodedendrons from North America. It isn't cold enough. I can grow tropical rhodies (Vireya) though.

[evtubbergh]

Ah, thanks. I wonder if so many plants really need cold temperatures or if they just live in places where they get cold temps? But I get the idea.

Yeah, I try to match the weather of where it is from to here but sometimes I can't find the climate information I need. Still, I mostly manage.

I was just wondering about a whole big map that only shows one end of the temperature range, never mind other information.