Growing fruit trees in the northernmost areas of the United States can be challenging. The key is to choose varieties which are reliably hardy in the USDA hardiness zone in which you live. "Reliably hardy" means that the variety will not only survive the extreme winter temperatures, but will also reliably produce a crop year after year. More varieties of plums can be grown in the warmer southern and coastal areas of Maine than in colder inland and northern areas.
All varieties of European plums (Prunus domestica L.) will survive in USDA hardiness zones 5 and 6 in the southern and coastal areas of Maine. The variety Seneca is an excellent cold-hardy plum which will grow well in zones 5 and 6 in Maine. In the colder areas of USDA hardiness zone 4, two hardy varieties that will grow well are Stanley and Mount Royal.
Asian plums (Puruns salicina), also called Japanese plums, are slightly less hardy than their European counterparts. All varieties of Asian plums will grow in USDA hardiness zone 6 in Maine. For colder zone 5 areas, the varieties Shiro and Methly have shown reliable hardiness. The coldest areas of Maine, in zone 4, are too cold for Asian plums to survive or reliably produce a crop.
Asian-American Hybrid Plums
The cultivated Asian plum was crossed with the smaller, hardier and wild American plum to form a series of hybrid Asian-American plums (Prunus salicina x americana) which show more hardiness than either European or Asian varieties. All Asian-American plum hybrids are reliably winter hardy through USDA hardiness zone 4 and can be successfully grown throughout Maine. Some varieties are LaCresent, Redglow and Toka.