Q.We Had A Hard Freeze In Colorado As Buds Were Starting To Form On My Nectarine Trees. Now, There Are No Leaves Coming Out, And Mos
t of the smaller branches are brittle. Are the trees dead? Any chance they will come back next year? The trees are about ten feet tall. I planted them in 2018, and they produced fruit last year. The only growth is a small branch about 5 inches long that has five leaf buds coming out.

Certified GKH Gardening Expert
There is a way to tell if a tree has died; here's an article about scratch testing: https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm
Citrus is not generally hardy in zone 5, but you say yours fruited last year? Do you take it inside over winter? Here are some hardy citrus that might fare better:
https://www.gardeningknowhow.com/edible/fruits/citrus/cold-hardy-citrus-trees.htm
https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-4/zone-4-nectarine-trees.htm