I think a lot of people have so-called micro-climates and take advantage without even realizing. For me, I usually head over to Mobot's site (Missouri Botanical Gardens) and see what they say - they're colder than me, but they do a lot of trials and have good info. Also, some of the nursery sites have good info (lazy's is very reliable). Dave's garden is also useful if it's a popular cultivar because people list their zip code of where they're growing the plant. If everyone who' successful is in Tennessee and you're in Idaho, it probably won't work out.

I find marginal plants, agastache for example, need exceptional drainage if I want them to live.

A loaded question, but as hinted at in the previous post, there's more to winter hardiness than the average low of a winter.

There's winter moisture on the crown of a plant, for instance. If you have poor drainage, that can kill an otherwise hardy plant. If you have good drainage, but the ground below that is a solid soil/ice layer, and it rains on top of that then *that* freezes, again, some plants die.
As a result, just covering certain plants over the winter with a piece of plastic allows them to survive.

Then there are heat zones. A plant that is "hardy" to a certain zone in the winter may not perform well in the summer heat that a zone creates. This weakens the plant, then it dies when trying to regenerate the next spring.

Or humidity levels. Alpine plants can be very hardy, for example, but treat them to the summer humidity of the midwest and they rot.

Or, plants that are hardy, but their flower buds die off at the edge of their hardiness.

I guess the answer is to ask local gardeners what works, and be prepared to lose a few plants in the inevitable "I want that" process!

I'm in agreement with much of the above. And will add that many responders on the forums state what works for them as universal truth for all gardeners. Micro-climates and soil conditions are just two of the many variables.

To my mind, I've found buying plant material recommended for my zone 4 (and I'm finding more and more plants that have been bred and grown in my zone and not trucked in from California and Florida, etc. which also attests to their probability of surviving my gardens and all their micro-climates) has proven much more successful than trying to get a zone 5 plant to thrive even with much special attention.

To be honest, trial and error in your own garden is a better guage then even asking other local gardeners. And it's simply because their conditions aren't exactly the same as yours. Having someone say "If I can grow it, anybody can" couldn't be farther from the truth... which is why I've totally given up on coreopsis, Monarda, Becky shasta daisies, Dutch Iris, and the new and improved heuchera varieties. I've had the old heucheras since they were simply called Coral Bells and they perform like troopers, but the new varieties just won't survive for me.

I could zone push and put in a much lusted after Japanese Maple - but my gardening sense tells me not to set myself up for disappointment. Yes, the zone hardiness maps are only guidelines, and they don't tell you the whole story. I've been gardening for many years and trial and error (even for what is rated as zone appropriate) is still a real good teaching tool.

duluthinbloomz4, I loved reading

"which is why I've totally given up on coreopsis, Monarda, Becky shasta daisies, Dutch Iris, and the new and improved heuchera varieties. I've had the old heucheras since they were simply called Coral Bells and they perform like troopers, but the new varieties just won't survive for me."

for a couple of reasons.

On the one hand, I feel better knowing that there's someone else who can't keep Becky going from year to year, and who strikes out with coreopsis. Becky, especially, should be easy... but not in my yard.

On the other hand, there's a part of me saying to myself "Monarda? You can't grow MONARDA? Of any variety? And Dutch iris is a problem? How can this BE?!?" ;-)

My zone rant: I've found it really frustrating the last couple of years that so many nurseries here are stocking z5 and even z6 perennials as though that's an accurate evaluation of my part of Minnesota. No, we're clearly north of the zone 4 line, on any map you see. We might've had several mild winters lately, but unless you have a special micro-climate that I don't, you can't count on keeping zone 5s going here.

Side note: The only time I've lost heuchera is when I've missed one in the fall mulching and then didn't notice that it had heaved completely out of the ground until it was too late. But that's only happened twice, and one of those was the old standby, all-green coral bells that's been around for years.

I don't really mind pushing the zone if I KNOW I am doing just that. I dislike finding plants at a local nursery that say they are perennial but aren't, such as tropical hibiscus or cannas. Cannas can be overwintered here, but you have to be careful of placement. On the other hand, I have purchased salvia Black & Blue here as an annual & it has overwintered at least 4 years now. That was a pleasant surprise.

I have great success with tall bearded iris and Siberian Iris, but the zone 5 Dutch Iris bulbs that show up in the stores in the Fall don't even sprout. Tried Monarda and it just disappeared - was then I decided I didn't like it well enough to try again. Would have liked the Beckys though - tried several times, each time buying three plants and putting them out in different spots...nada.

The first year I had Beckys we went down to -15°F. I lost half of them, and decided when the catalogs described them as 5b, they weren't kidding. So I'm not replacing the Alaskas by the road any time soon.

What has started showing up here are quite pricey zone 6 conifers. There is a theory that a certain number of them will be heading south, but if they aren't.... Is a zone 6 plant really a zone 6 plant if it can handle multiple -15 winters?

Interesting thread. I have, for a few years now, suspected that some of the wholesale growers try very hard to word their little plant "tags" (you know the little plastic information tags they stick down in the pot with the plant) to make the plant sound like 'one size fits all'. Sort of trying to make the plant sound like it will thrive just about anywhere in the U.S. in the hope that more unsuspecting gardeners will buy them. AND as long as I am griping, another thing that frustrates me... I know it is crucial to know how cold hardy a plant is, but I have bought lots of plants in the past that, although they survived the winter, they melted and withered away in the intense heat and humidity of a Ga. summer. Now, if I buy any plant that I have not tried before, I research it thoroughly on the internet..

Some times zone pushing works. I was just admiring the silver bells (ornithagalum nutans) whch are supposed to be zone 6 and I've had them for at least five years now. OTOH, artemisia Powis Castle bit the dust this past winter though it survived the previous one.
And after numerous tries with salvia argentea, I've finally had success by planting it on a bank that is almost pure sand. It loves the sharp drainage and has gone through several winters now.
Interestingly, hydrangea Endless Summer survives our winters but is a shy bloomer for me. My sister in Maine (also zone 5) has a gorgeous plant of it which does flower all summmr long. Maybe because it's in a more protected spot?

mad_gallica, you said about Beckys

"when the catalogs described them as 5b, they weren't kidding".

Problem is, when I see them at the nurseries up here, they're labeled as hardy to z4. Clearly, they're not.

Meanwhile, I have these big holes in the garden right now that are all fenced against rabbits and labeled "Becky" that have nothing green emerging.

It's frustrating; I wouldn't have even bothered if they'd been labeled 5b, because I know I don't have a microclimate that would support them. Grrrr....

We had some landscaping replaced last year - the 40 year old yews that were here when we moved in in '06 just had to go! I picked plants that I wanted, buying some myself, and others were supplied by the landscaper at my request.

I had seen a gardenia that was supposed to hardy to zone 6 and wanted to give it a try. It was planted next to a red brick house, and since the brick can hold heat, I had hoped that I would be able to grow and keep my hardy-to-zone-6 gardenia. Well, it was alive just until the middle of January, when our cold, winter weather really started. I'm upset that I lost it, but I was prepared for it. Would I try something else that was supposed to be hardy to zone 6? Maybe. It would depend on how bad I wanted a particular plant. I usually try to find things for my perennial beds that the tag says are hardy to Zone 5 and that makes me feel safer.

Linda

PS Shasta Becky does grow well here, but I killed a piece of Crazy Daisy that a friend gave me last summer. I just bought it again, and am giving it another try.

I just guess. I've got spots with good drainage where I'll try anything that is supposed to not be wet in the winter, but it's an exposed site. I've got spots by the house for things that need more protection, but those get wetter. I lost Agastache cana (I think) last winter, but Sinning and Black Adder which are also supposed to be marginal came through fine. Agastache Sinning was even in a fairly lousy spot by the mailbox. I'm trying Agastache Purple Haze this year. It was pretty, fairly cheap, and I think it's worth a shot. My coreopsis came through fine and my Heucheras made it through the winter in a spot where I've killed everything else I've tried there. So if I like a plant well enough, and it isn't too expensive, then I'll try it and ignore the zones. I haven't had the courage to try a Japanese Maple yet, but I've found a cheaper source and I think I'll try one next year.