Leo in N E Illinois
The Professor
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I thought I would just post this list as a new thread, just so people can find it when they are looking for it. I am a fan of using elms that are fully winter hardy in your local climate. There has been much talk about the southern USA native elms, like Ulmus alata, winged elm, and Ulmus crassifolia - the southern cedar elm, but both these elms do not fare well in colder climates. So I hit my favorite friend, Wikipedia, and combined with some information I gathered other places, I compiled this list.
Elms for USDA zone 5 and zone 4 - these species should be able to be wintered, outdoors, without temperature protection, pot set on ground, protected from wind & maybe sun, mulching in optional.
Ulmus americana - American elm, in the landscape susceptible to Dutch elm disease, in a pot treatment is relatively easy. Leaves will reduce dramatically, almost as much as Chinese elm. Native to most of North America. Really good for bonsai
Ulmus thomasii - rock elm, also known as northern cedar elm, but it is not the same species called cedar elm in the southern USA. Native to northern Midwest America, into Canada.
Ulmus parvifolia var coreana - the Korean ecotype of the Chinese elm. Chinese elm from southern China may, or may not be winter hardy in zone 5, the Korean ecotype has survived through -29 F (-34 C) in trials at the Morton Arboretum in the west suburbs of Chicago. The Chinese elms I have tried, of unknown origin did not do particularly well. Worth experimenting with different sources. Note, in my experience, the named varieties of Chinese elm, like 'Corticosa', 'Hokkaido', 'Sejiu' and 'Yatsubusa' all seem to require at least some winter protection. Your best bet to find truly winter hardy U. parvifolia is to try one of the un-named seedlings. If you can find seed sourced from Korea, this is your best bet.
Ulmus pumila - the Siberian elm - superior winter hardiness, an invasive species, to keep lower branches from weakening and dropping off, absolutely must have full sun pretty much from sunrise to sunset. If given enough sun, it works well for bonsai. Probably good into USDA zone 3, it is extremely cold tolerant. Nice rough bark even on fairly young trees.
Ulmus glabra - the wych elm - this is the most northern, cold tolerant of the European elms - there is a tree or two surviving in Greenland. If you can find it, it can work in zone 4.
Ulmus rubra - native to the northern midwest NA into Canada, the Slippery elm, or red elm - looks like an American elm except "chiefly distinguished from American elm by its downy twigs, chestnut brown or reddish hairy buds, and slimy red inner bark" - flowers in spring before leaves appear, and flowers are reddish. This elm is a little bit more shade tolerant than some other elms. Still, full sun is usually best for cultivation.
Ulmus minor - the Field Elm - a widespread European elm that is very cold hardy. Possibly invasive in some areas of USA.
So the above are either native to the USA or somewhat available in commerce. The few below you are very unlikely to encounter, they might be hardy.
Rare in North America elms that might work - Ulmus davidiana, Ulmus glaucescens, Ulmus macrocarpa, Ulmus bergmanniana, Ulmus lamellosa,
This list is only a complete as the information from Wikipedia. There might be some trees I omitted. Apparently someone from the elm evaluation and breeding program at Morton Arboretum, in the western suburbs of Chicago had edited in some good information into Wikipedia.
Virtually all elms, or at least every elm species I have seen bonsai attempted with, has performed nicely. I believe pretty much all elms can make good bonsai. All will develop reasonably fine twig patterns. All the leaves will reduce to relatively small size. True that Chinese elm and Siberian elms have leaves that can be kept at 1/4 inch or 0.6 cm, but all the other elm species have leaves than can eventually with ramification be kept at or under 1 inch or 2.5 cm.
So where ever you live, if you have elms growing in your landscape, dig one up and give it a try. If, like the west of the Rocky Mountains, USA, you don't have elms everywhere, this list is for the norther group of you. Hopefully all of those in the high plains that wanted to try elms can get a hold of some of the elms from this list.
Elms for USDA zone 5 and zone 4 - these species should be able to be wintered, outdoors, without temperature protection, pot set on ground, protected from wind & maybe sun, mulching in optional.
Ulmus americana - American elm, in the landscape susceptible to Dutch elm disease, in a pot treatment is relatively easy. Leaves will reduce dramatically, almost as much as Chinese elm. Native to most of North America. Really good for bonsai
Ulmus thomasii - rock elm, also known as northern cedar elm, but it is not the same species called cedar elm in the southern USA. Native to northern Midwest America, into Canada.
Ulmus parvifolia var coreana - the Korean ecotype of the Chinese elm. Chinese elm from southern China may, or may not be winter hardy in zone 5, the Korean ecotype has survived through -29 F (-34 C) in trials at the Morton Arboretum in the west suburbs of Chicago. The Chinese elms I have tried, of unknown origin did not do particularly well. Worth experimenting with different sources. Note, in my experience, the named varieties of Chinese elm, like 'Corticosa', 'Hokkaido', 'Sejiu' and 'Yatsubusa' all seem to require at least some winter protection. Your best bet to find truly winter hardy U. parvifolia is to try one of the un-named seedlings. If you can find seed sourced from Korea, this is your best bet.
Ulmus pumila - the Siberian elm - superior winter hardiness, an invasive species, to keep lower branches from weakening and dropping off, absolutely must have full sun pretty much from sunrise to sunset. If given enough sun, it works well for bonsai. Probably good into USDA zone 3, it is extremely cold tolerant. Nice rough bark even on fairly young trees.
Ulmus glabra - the wych elm - this is the most northern, cold tolerant of the European elms - there is a tree or two surviving in Greenland. If you can find it, it can work in zone 4.
Ulmus rubra - native to the northern midwest NA into Canada, the Slippery elm, or red elm - looks like an American elm except "chiefly distinguished from American elm by its downy twigs, chestnut brown or reddish hairy buds, and slimy red inner bark" - flowers in spring before leaves appear, and flowers are reddish. This elm is a little bit more shade tolerant than some other elms. Still, full sun is usually best for cultivation.
Ulmus minor - the Field Elm - a widespread European elm that is very cold hardy. Possibly invasive in some areas of USA.
So the above are either native to the USA or somewhat available in commerce. The few below you are very unlikely to encounter, they might be hardy.
Rare in North America elms that might work - Ulmus davidiana, Ulmus glaucescens, Ulmus macrocarpa, Ulmus bergmanniana, Ulmus lamellosa,
This list is only a complete as the information from Wikipedia. There might be some trees I omitted. Apparently someone from the elm evaluation and breeding program at Morton Arboretum, in the western suburbs of Chicago had edited in some good information into Wikipedia.
Virtually all elms, or at least every elm species I have seen bonsai attempted with, has performed nicely. I believe pretty much all elms can make good bonsai. All will develop reasonably fine twig patterns. All the leaves will reduce to relatively small size. True that Chinese elm and Siberian elms have leaves that can be kept at 1/4 inch or 0.6 cm, but all the other elm species have leaves than can eventually with ramification be kept at or under 1 inch or 2.5 cm.
So where ever you live, if you have elms growing in your landscape, dig one up and give it a try. If, like the west of the Rocky Mountains, USA, you don't have elms everywhere, this list is for the norther group of you. Hopefully all of those in the high plains that wanted to try elms can get a hold of some of the elms from this list.
