Cold Hardiest: Burr Oak (Zone 3a)

Least Cold Hardy: Live Oak (Zone 7a)

My generic Arbor Day Acer rubrum claims zone 3 if I recall.

My Crepe myrtles are zone 6ish barely, really 7 if you take hardiness to mean it never dies to the ground in winter.

Most hardy: Picea abies 'Gold Drift - zone 3

Least hardy: Eucryphia lucida 'Spring Glow' - zone 8/9

btw, both of them are grown in containers (as are all my trees) and are several years old (~5 or so)

"Only true trees count; so, palms don't count here."

A palm tree is every bit as much of a "true tree" as any of the others listed above! I've always been baffled by the claim that trees, like palm trees, are not "real trees". Maybe you are just wanting to exclude monocots (for whatever reason)?

I've seen others people (especially one frequent GardenWeb user) claim that conifers are not trees. Never really understood that either.

Without listing monocots (for Subtropix) or conifers (for you know who), here are some of mine:

Fagus grandifolia, Ginkgo biloba, Gymnocladus dioicus, Maackia amurensis, Prunus avium, Quercus alba, and Quercus macrocarpa are all typically rated down through at least zone 3.

edit: I didn't read the instructions well, so probably shouldn't have listed anything. I have a few plants that push my zone, but nothing exceptional in that category. I have a few with a minimum hardiness rating of 7, but nothing more than that, that comes to mind right now.

Where are the Californians? Surely they can win this contest hands down. Unfair advantage LOL. At Mendocino Coast Botanic Gardens I'm pretty sure I saw a Leucodendron argenteum (considered no more than 9b hardy...and some say 10a) and various zone 3 conifers. Or the 9a rated Rimu tree, or various 9a rated Asian BLEs. At the Huntington in LA, I'm sure there are various 10a trees (like the famous rainbow Eucs) and somewhere a zone 3 or even 2 conifer or two.

Brandon I think he meant the minimum hardiness rating for each group of species, not the maximum of the range.

Heh, Brandon, it's all about definitions. So, if a tree is a large-growing, woody, compartmentalizing organism, by that definition, palms are indeed not trees, as they lack the ability to compartmentalize wounds and don't lay up concentric rings of new growth each growing season as true trees do. But if one were to say that a tree is any sufficiently large-growing plant with a main stalk (trunk) and foliage diverging from this stalk, then yes, palms would be included.

They really are vastly different from trees, these palms and cycads...and some of them do not get tall. I think it reasonable to exclude them from being actual trees, although they are surely valuable and interesting plants in their own right. For me, few botanical sights in S. Florida top the viewing of such items as old-growth bald cypress in Corkscrew Swamp, but with the equally native and aesthetically amazing royal palms growing in close proximity to each other.

Conifers? Yeah, they're trees by golly, except for those that aren't, lol, like shrubby junipers, etc. But I digress, and in truth, there's a difficult dichotomy, that between trees and shrubs!

Cold Hardiest: Larix laricina (Zone 2..is anything ever actually rated zone 1?)

Yes, populus tremuloides, american aspen is zone 1. So are abies lasiocarpa and alnus tenuifolia. And larix gmelinii, the most cold hardy tree in the world. It can tolerate -95F, way outside the USDA zone system.

I don't grow any of those though, I'm between zone 2-6.

Probably 'Granny Smith' apple - zone 5

Quercus acuta - zone 8 or 9, depending on what site you look at (even though I live in zone 7!). Hey, it's still alive after one winter!

"as they lack the ability to compartmentalize wounds"

Hhhmmmm. But some palms can sucker which seems like a roundabout but effective way to "compartmentalize". Seems to me they serve the same ecologic niche as angiosperms and conifers in many cases, so have every right to be considered trees.

I agree with Tom - it's all about the definitions. The designation of a "tree" only describes a particular growth habit, not a specific type of plant. The most commonly accepted definition is this: 'a woody perennial plant, typically having a single stem or trunk
growing to a considerable height and bearing lateral branches at some
distance from the ground'. By that definition, palms should fit the classification although some may argue about the branching aspect.

And I assume Brandon's little dig about conifers not being trees is directed at me - he never misses a chance be demeaning with regards to any of my comments. And if he was accurate - which has never been his strong suit in this regard - my comments were only to clarify another GW member's insistence that ALL conifers are trees, which they are not. Many DO fit the accepted definition of a tree but just as many fit the description of a shrub or even a groundcover, in that they do not produce a single trunk "growing to a considerable height' or bearing branches at some "distance from the ground". It takes a pretty good stretch of the imagination to consider a Blue Rug juniper a "tree"!!

burr oak -- zone 4 & maybe 3 -- depends on source.

pond pine -- zone 8 (some references), zone 7b others. This one shows no adverse cold effects here so far.

coconut palm -- just kidding.

Yes, I must confess, I am driven by deep monocot hatred. Dam/ those wannabe palm "trees". No, they may not be classified as true trees by the plant experts (i.e., botanists)..., but, just so happens, I grow more species of those fake, wannabe trees (i.e., PALMS) than any thing else. LOL, virulent palm hatred here is my MO. Yes, Brandon you are right. Whateve'.

"No, they may not be classified as true trees by the plant experts (i.e., botanists)"

But I'd actually like a citation from google books or something, of a currently active botanist so classifying them. I somewhat doubt that is the prevailing definition.

Ok, not that wikipedia should be the final word on anything, but it says this...so we might have to agree to disagree haha:

Although "tree" is a term of common parlance, there is no universally
recognised precise definition of what a tree is, either botanically or
in common language.

Davidrt28, you are absolutely correct about the minimum hardiness rating thing. I was distracted and didn't read carefully. I grow a few things that "push my zone limit", but nothing exceptional in that regard. Most all of my trees are hardy to at least zone 7, so I won't even bother listing anything in that category.

Gardengal, you surely owe me a BIG APOLOGY! I was in NO WAY talking about you. You hadn't even entered my mind about this subject. I am unfamiliar with the conversation you seem to be so sensitive about. Again, your assumption that I was talking about you in ANY WAY, is COMPLETELY WRONG! In fact, after re-reading your post, your assumption doesn't even make any sense to me.

Subtropix, I am unfamiliar with any botanists that believe monocots can't be trees. I think you may have misjudged the typical botanist's opinion on the subject. But hey, it's your thread, so if you want to exclude monocots (for whatever reason), that's fine. I just hate to see "re-definitions"; it's not the limitation on the results that concerns me.

All this reminds me of another limitation I sometimes see on trees. I have actually seen more than one person on here claim that trees with more than a single trunk aren't trees. I never understood that one either.

Brandon, if you were not referring to me then you do have my sincere apologies. We have had our contretemps from time to time and I made a very erroneous assumption that this was another in the series. I am indeed sorry.

And if you have any ongoing curiosity as to how that reference came to be, just visit the Conifer forum sometime.....it will become readily apparent

No longer my garden, but growing up, we had apples and plums. Both of which are zone 4-ish (but I don't know specific cultivars, so I may be wrong). We also had a trident maple and another maple that I've yet to figure out what type it was. Also, a box of some sort, an English oak, a pussy willow, another evergreen oak that I haven't yet figured what type, and a mulberry that gave us delicious dark purple mulberries each year. None of which were native to the highveld region we lived in.

Warm climate plants included silky oaks, wild olive, black wattle, white stinkwood (celtis africana), tipuana, loquat, jade plant (gigantic - it makes me sad when I see the teeny little ones sold as house plants here in the US), a beautiful bauhinia, avocado, deodar cedars, and probably others I've probably forgotten.

For what its worth, the unidentified maple and the box both turned up their toes and died during a severe drought with punitive watering restrictions. (And if anyone could hazard a guess as to what kind of maple is wider than tall, with a lovely upsidedown bowl shape to it, and yellowish autumn leaves - although that might be climate related, although the trident had glorious reds in autumn - and would be okay growing in a dry, summer rainfall, warm climate up until the drought that killed it, I'd be grateful if they could share. LOL)

Not trees, but we also had a yesterday-today-and-tomorrow (brunfelsia) growing right next to a flowering quince.

I am curious as to how one can know what the 'most or least hardy' trees are. If it hasn't died how can one tell if it is at its limit?

Floral, practically, one would need to rely on reports of typical hardiness ratings for the type of plant. The typical hardiness rating of most common plants is generally available. Rare and unusual stuff may be harder to pin down.

The most cold hardy of mine will probably be White Oak or Bur Oak, both of which normally grow further north of here anyways.

Least hardy is likely to be my 'Giombo' kaki persimmon.

Ah, it is probably a tad unfair since Britain is famously temperate with a mild maritime climate...such that allows for the growing of loquats (next to a sheltering wall) and my fickle Meyer lemon...and yet we also grow cold hardy crabs, sorbus and poplar. My local botanics has a remarkable set of eucalypts and also a gorgeous specimen of the chilean myrtle, so here in dry East Anglia, it is possible to range from 2-9 with only a few seasonal protections

Exactly. A huge range is possible so I can't really come up with any examples. Maybe my avocado which grew from a pit in the compost heap and is staggering into its 4th summer now, albeit looking terribke and still only two feet tall .... But definitely alive.

"such that allows for the growing of loquats (next to a sheltering wall) and my fickle Meyer lemon."

Camp, you don't mean you have a Meyer Lemon outside? In years of following various www boards with many English posters, I always got the impression that outdoor citrus (other that P. trifoliata perhaps) didn't do much there because it was simply too cool in summer. Even in very mild places like the SW coast. Anyhow I would have expected that comment more from floral, given the milder climate in Cornwall. Even the Meyer Lemon is usually only rated 9a, though it's hardier than other lemons. OTOH, as I posted there was a report of a mango getting somewhat substantially sized, in a sheltered London courtyard, during some mild winters of the 1990s. Probably from a discarded seed. So maybe things like Meyer Lemons can subsist in mild areas there with the acceptance they are unlikely ever to bear.

I did know Loquats grew there as it's not an unusual plant to see in London gardens at all.

Most Cold Hardy: Juniperus scopulorum 'Tolleson's Weeping' (Zone 3)

Most Cold Hardy - Non-conifer Division: Tie between Prunus cerasifera - Purpleleaf Plum and Betula nigra 'Summer Cascade' (Zone 4)

Least Cold Hardy: Spathodea campanulata - African Tulip Tree (Zone 9b or 10-11 depending upon source)

ETA Forgot the Betula.

Picea engelmannii - Zone 2

Picea torano - zone 6 - grows great here with no hardiness issues. I think they got it wrong; Should be zone 5.

Dax

Edit: I can't grow engelmannii on its own roots. I've tried over and over again with seedlings and they perish during summer when spring planted. Grafted engelmann on other Picea species - it grows fine.

Cold Hardiest: Quaking Aspen (Zone 1)

Least cold hardy: Citrangequat (Zone 7b/8a)

Davidrt28 - just to be clear. I live in the SW but don't live in Cornwall.

Meyer Lemons do fine here outdoors in Summer. It isn't too cool. They do need to be brought inside in the Winter, normally. But Campanula appears to have managed to get hers through outside with protection. I had a Meyer in a pot for about 15 years and it usually came into the porch (unheated) from December to March. But a few years I just left it outside in a sheltered spot and it survived.

Thanks floral. Do you see any outdoor citrus there in collector's gardens, besides P. trifoliata? The various intermediates (hardy X non-hardy) are surprisingly hardy in the US SE, but again we have blistering hot summers to cook the wood so that might be a difference. And most of them are inedible novelties, you don't really get into the "edible zone" until you are down in coastal SC, and even then it's only the very hardiest satsumas or semi-edible hybrids. I have a seedling of "Dunstan citrumelo" which survived, barely, the 2 horrendous winters you probably heard about. I'm always hoping I'll have that one in a million mutation and it won't be bitter LOL. It's a few years from bearing, assuming it isn't cut to the ground again.

I've never seen any Citrus in the ground except in a walled garden on the Isle of Wight. Maybe Campanula has.