Underwood Plum

Overview

Underwood is a classic cold-climate hybrid plum known for dependable survival in relatively harsh winters and for producing attractive, flavorful fruit that works well for both fresh eating and processing.

Origin and History

Underwood is a University of Minnesota introduction from the early 1920s. According to the bilingual plum reference hosted at Cyberfruit, it was introduced in 1921 by the University of Minnesota Fruit Breeding Farm (Excelsior, Minnesota) and is described as a hybrid-type plum derived from Shiro × Wyant. (cyberfruit.info)

Underwood sits in the “Japanese–American hybrid” category that many northern-region plum programs leaned on to combine improved fruit quality with the ruggedness of native North American plum species. (Utah State University Extension)

Fruit & Uses

Underwood fruit is large for a hardy hybrid plum, with dark red skin and yellow flesh. The fruit is juicy, melting, and tender, ripening around mid-August in Missoula, and it also holds well in cold storage.
In practice, Underwood can be enjoyed fresh when fully ripe, but it also (apparently) works well in sauce, jam, fruit leather, baking, and fermentation, although we have only ever eaten it fresh.

Growth Habit & Spacing

Underwood grows as a medium-sized plum tree rather than a true dwarf. That said, it will grow with slightly more vigor on Krymsk 86 rootstock than on Native American plum, although the latter may be ever so slightly hardy for growers that can potentially see -40F or colder. We'd put Krymsk 86s hardiness at -40F until we have more data, whereas Native American plum is probably closer to -50F. Space Underwood on Krymsk 85 at least 15 ft. apart. Native American Plum can be 12 ft apart. For either of these rootstock, you could also plant closer under a more extensive pruning regiment.

As with many hardy hybrid plums, good air drainage matters because hybrid plums bloom early (right after peaches) and can be more “spring-frost limited” than “midwinter-cold limited” on marginal sites.

Pollination

Underwood is not a “plant-one-tree-and-forget-it” plum in most climates. It needs a compatible hybrid plum nearby for consistent fruit set. Pollenizers for Underwood include Alderman, Pipestone, Hanska, and Gracious, Toka, Kuban Delight, Ptitsin #5, La Crescent, Superior, and other Asian–American hybrids. Native American plum and Prairie Red can work as pollenizers for these hybrid types as well.

Cold Hardiness

We have observed Underwood surviving -38F in Stevensville, MT from a 1/13/24 polar front without showing any signs of winter injury. St. Lawrence lists Underwood as hardy to -50F with occasional winter injury. Because we cannot verify this claim in our experience, we are conservatively saying Underwood is hardy to -40F. Hardy to zone 3a.