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. These Underwood plum trees come in several different rootstock/sizes for Spring 2027. They are either on Native plum, which is likely slightly hardier, and tends to produce a semi-dwarf tree in our dry, alkaline soils and harsh climate. However, key word there is 'tends'. We have found that there is some natural variation in the size of Native Plum as a rootstock (and in general as a stand along tree) as these plants are grown from seed. However, the other rootstock we have grafted Underwood onto is Prairie Red, which is far more uniform according to Dan Sheild, produces a semi-dwarf tree (roughly 15 ft. at maturity or slightly larger in deeper soils), and is hardy to around -50F.

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.