Sour cherry trees can pollinate sweet cherry trees. I'm not sure if they make the best pollinator, but they are certainly capable of doing so. If you take a cherry that resulted from a blossom that was cross-pollinated here and take out the seed, that seed can grow into a hybrid tree, which can eventually produce fruit of its own (I know that in the case of the hybrid cultivar 'Mesabi' it's even self-fertile). However, the seeds inside this fruit are sterile and cannot grow. Like breeding a horse and donkey together to create a mule, there is no third generation. The reason is a chromosomal difference, sweet cherries are diploid (2n=16) while sour cherries are tetraploid (2n=32). A hybrid between the two results in a triploid cherry, which is why it cannot further sexually reproduce. However, flowering cherry species just happen to have the same chromosome count as Prunus Avium (i.e. sweet cherries), so that means they are capable of freely interbreeding. But it should be noted the two are still not in the same species. The question then is what does this really mean? Even when it comes to the different wild varieties of Japanese flowering cherry, oftentimes crossbreeding them together results in a hybrid that grows less vigorously than its parents, or is not very well adapted to its environment. Sometimes this may become more evident several generations down the line (you might read up more on how Outbreeding Depression works). Cultivated varieties of flowering cherry, almost all of which resulted from hybridization over hundreds of years) are much less hardy than their original wild pure-species relatives. We can even see some level of graft incompatibility combining different varieties of cherries within the same species, the tree does not grow quite as vigorously or as big as if it were grafted onto its own rootstock.

The "looseness" of the roots suggests that perhaps roots were not sufficiently loosened at planting so that they remained in the planting mix rather than penetrating the surrounding soil. If the effected branches are last year's growth, that would usually mean winter kill - a combination of cold, wind and wood that is not fully ripened. The crisping leaves on a main branch suggest a problem at the roots - no moisture is getting to the branch. (If most of the roots are still in a peat based planting mix, root rot could have set in because of excessive moisture.) Cherries are prone to many maladies and conditions this year have been perfect for many diseases. Is it worth trying to save the tree? Sure. Prune back to live wood. If possible, dig up, prune off any rotted roots and replant, making sure that the planting hole is not a "bathtub" that retains excessive water.

A Bing cherry tree growing in southern California will do reasonably well the first several years, just enough to get your hopes up. After that, it will start dwindling away, more & more each year. And will eventually look so sad you'll remove it. If you want a tree that will grow and produce cherries, ask at your nearest independent garden center which cherry will do well where you live. Several will. But only if you obtain the correct kind. Ask when it/they will be available. (In SoCal, bareroot tree fruits are generally available during Jan. & Feb; sometimes in Dec.) As for the flowering cherries and other trees that require substantial amounts of chill -- total hours between 32 and 45 during Dec, Jan & Feb, but subtracting all hours above 65F -- will grow but will bloom erratically & will leaf out erratically. So save yourself a lot of grief and grow "low-chill" fruit tree(s) suited to your region. The large garden centers know which ones they are. But you need to ask. One big problem: Just because a garden center in your region sells a specific fruit tree doesn't mean it will thrive there. Jean, who gardened in Long Beach, CA, for 30-some years.

two thoughts ... first.. if you have had prior trouble.. in your area.. why beat your head on a wall ... try something else .. second.. if there are 4 across the street.. within view... why do you need 5 .. let the neighbor deal with them .. diversify ... there are plenty of other flowering .. care free trees.. to plant ... e.g. redbud ... etc ... got to tell us where you are.. to hear about alternatives ... YCs are a rather short lived tree .. a decade or so .. is about all you get .. and then they start to go down hill ... plant something else ... ken