Zone 4, the area around Minnesota and Montana, requires plants that can live in -30 to -20 degrees F. The best trees for clay soil in zone 4 can come from many of the evergreen varieties. Clay soil trees need to be able to be hardy and live in a harsh soil type. These zone 4 trees have proven to be good specimens for clay soils.
The littleleaf linden is from the Tiliaceae (linden) family under the botanical name of Tilia cordata. It is a fragrant tree that reaches a height of 90 feet with a 50 foot spread. Heart shaped leaves are 3 inches long and fragrant yellow flowers are less than an inch wide. Plant a littleleaf linden tree in full sun with moist well drained soil. Propagate via seeds, layering, sucker division, or by bud grafting.
The American hornbeam is from the Betulaceae (birch) family under the botanical name of Carpinus caroliniana. It can get to a height of 50 feet tall with a 40 foot spread but 15 to 20 feet is more normal for the height. Leaves are 2 to 4 inches and oval with nut fruits. Plant an American hornbeam in shade or sun with well drained soil. Propagate via seed.
The European larch is from the Pinaceae (pine) family under the botanical name of Larix decidua. It can get 70 to 100 feet tall. It will have light green needles and brown cones. Needles will yellow and shed in the fall. Plant a European larch in moist well drained soil in full sun or partial shade. Propagate via seed.
The Norway spruce is from the Pinaceae (pine) family under the botanical name of Picea abies. It is an evergreen that can get 80 to 150 feet tall and 20 feet wide but normally is 50 feet tall. Needles are blue green to gray green and cones are reddish brown and 4 to 6 inches. Plant a Norway spruce in well drained neutral or acidic soil with full sun. Propagate via seed in spring, grafting, or by summer tip cuttings.
The black willow is from the Salicaceae (willow) family under the botanical name of Salix nigra. It is a fast and easy growing tree that can get to 65 feet tall with green leaves that are lance shaped. Plant a black willow in full sun or partial shade. Propagate via cuttings.