The clover/ calendula planting sounds pretty good. Those will promote a good microbiome that will help the sour cherry tree along.
You might look for some other plants that will pull up other nutrients for planting out around the drip line area so you are improving soil health all around the feeding roots of the tree as well.
If you have it available in your area, plantain, daisy, Echinacea, things like those will benefit the tree root system as well.
Keep in mind water needs of the plants you utilize as tree helpers, you don't want the tree's water needs to suffer any losses.
some mushroom spawn via slurry inoculation would be good as an addition too.