Thank you for contacting the UVM Master Gardener Helpline with your question about your Nanking cherry bushes. Unfortunately, it’s hard to tell from your pictures what is happening with your bushes.

It would be helpful if you included pictures that show the soil/mulch level around the bush stem or trunk. This article entitled “Mulching Trees and Shrubs” published by the University of Maryland Extension provides guidance on proper mulching techniques.  https://extension.umd.edu/resource/mulching-trees-and-shrubs   In particular it is important that the soil level remain consistent with the original soil level before you planted it on your property. If you mulched, make sure you leave a donut hole space at least 3” between the mulch and the base of the shrubs. If the soil or mulch is too far up the stem it will kill the bush.

You don’t mention when you planted the bushes. Was it last fall, this spring or a previous year? Is it possible the roots on the failing plant dried out while you planted the other? In the “Planting” section of this Cornell University article entitled “Guide to Growing Fruit at Home” (https://ecommons.cornell.edu/server/api/core/bitstreams/60165302-b299-433a-952d-9ac82cc63849/content) you will find information about best practices for planting your shrubs.

Is it possible that the roots on the failing shrub were more compacted or not as healthy before you planted them on your property?

You can also look for any signs of insects or fungus on the underside of the leaves and around the branches/stem of the shrub.

Does one of the shrubs get more or less water than the other? Any exposure to problematic run off from a lawn or road?

You might want to consider doing a soil test to make sure that your soil is ideal for growing your shrubs. You can submit a soil sample to the UVM soil testing lab following the instructions found here: https://www.uvm.edu/extension/agricultural-and-environmental-testing-lab

Links to some other information you might find useful:

“How to Grow Nanking Cherries in Your Garden” published by the Utah State University Extension has specific information about Nanking cherries : https://extension.usu.edu/yardandgarden/research/nanking-cherry-in-the-garden

The International Society of Arboriculture ”Trees are Good” site has lots of information you will find useful: https://www.treesaregood.org/treeowner

I hope you find this information helpful. If you want to follow up with pictures of the shrub branches/soil, any signs of insect or fungal damage, or have any additional questions, please feel free to reach out.