I was out on the south hillside of our small property today where the wild plums grow, and I snapped this photo of the buds. Unfortunately, these plums always bloom early and are almost always caught in a late frost. The warm days on the south-facing bank trick them.
We have another small plum thicket where the ground slopes slightly to the north, and even though they have full sun, they don't bloom until after the last frost and they usually bear fruit.
I started all of our wild plums from seeds. I was given some local wild plums, a sour yellow variety, and I saved some seeds and planted them. The next year, I happened to be in Kansas when the wild plums were fruiting, and I brought back a mess of plums and planted some of their seeds with my local plum seedlings. This was a sweet yellow plum. I can't tell any difference in the appearance of the trees or the fruit, but I can certainly tell which is which by the flavor.
Wild plums send up a lot of suckers, and their natural tendency is to form a thicket. We put them on a sharp bank in our yard that we don't want to mow, and they are doing a good job of taking over. The trick is that you must stop mowing the area where you want the thicket to develop.
I read tonight in a U.S. Dept. of Agriculture publication that three cultivars have been developed from the American wild plum: 'Blackhawk', 'Hawkeye', and 'De Soto.' I would guess that they are sweeter and larger than most wild plums.
I have written more about my personal history with the wild plum in an article on my other blog, Prairie Bluestem. Please see "Wild Fruits of the Nebraska Sandhills"