To be honest, Steve, this time I didn't covered them because the only trees that were in bloom were my Indian Free Peach tree, and my neighbor's peach trees were just starting to flower. I also didn't bothered to covered them because bee activity was very scarce this year, so the chances of pollen contamination was very low, that's what I think.
By the time that I created this thread, a week had already passed since I started hand pollinating the cherry flowers. So those fruits that appear in the pictures are from the first flowers that started to bloom. To help me remember which flowers I pollinated with peach pollen, I marked them with red yarn.
At first, I had no plans of creating a peach x cherry hybrid. I decided to cross pollinate them with peach pollen because there were no cherry trees blooming with Rainier so I didn't wanted this tree to go fruitless or with a few fruit this year. I also invested a lot of time and money on this cherry tree, so I didn't wanted my efforts that I put on this tree to go to waste.
I also pollinated the last blossoms with Tartarian, Bing, and Stella Cherry pollen. However, those flowers haven't developed into fruit, yet. All these three cherries started blooming this week.