Sorry for the topic wander but I wanted to followup to ensure my comment info was correct.
Back to topic, I don't notice any seedlings around either cherry, but do get tons of suckers on the sweet cherry, both from the base of the tree and off the roots. I think most sweet cherries are on grafted rootstock, not sure how that may affect your seedling (it may have a weaker root system). Good luck with the seed experiment and let us know how it turns out.
