Jay

Hi, I have attached for your inspection a web site you may want to look at, excellent info. I have also given you his write up on this elm. As for minumum temps, I do not have this cultivar but my elms have no trouble with temps in the teens or slightly lower.
http://www.evergreengardenworks.com/
Ulmus parvifolia 'Hokkaido' (Princess Elm) There are hardly enough superlatives to adequately describe this plant. An extremely tiny elm with 1/8 inch leaves congested on small dark brown stems sometimes 20 to the inch. Thirty year old plants may reach about 3 ft. with 12 inch or greater very corky trunks. Despite its small stature this plant is not especially slow growing; 4 year old trees may be 10 inches tall with 1 inch or greater trunks. Corky bark begins developing almost immediately. Some people report that they have trouble growing this tree, and it almost always can be traced to over-protection. This tree thrives in full sun and even partial shade can bring its demise. Bonsai plants can tolerate afternoon shade in hottest driest areas. Needs good drainage and regular even water but not wet conditions which will cause root and crown rot. The wood is extremely brittle and even a casual brush by the plant may snap off 1 inch branches. Wiring is nearly impossible and any significant shaping must be achieved through pruning.

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A Bonsai student living with his trees at N 44.37 W 77.49...
Think before you act... then think again... no good comes from rushing