I bought two bare root pear trees six years ago, a Comice and a Bartlett. I bought the Bartlett primarily to serve as a pollinator for the Comice. I grew them in containers for the first year (I knew I would be moving), then put them in the ground a year later. Both trees began flowering at the beginning of the third year. However, the Bartlett flowered right as the Comice flowers were falling, so I got no cross pollination. I thought perhaps the flowering cycles were permanently out of synch, so a few years ago I grafted several scions from the Bartlett onto the Comice, in the hope that the parent Comice would control the flowering of the Bartlett scions. Instead, the Comice stopped flowering altogether. This is the third year of virtually no flowers on it. Even the Bartlett scions, now well established, produced very few flowers (but a couple of them did set fruit.) Both trees are planted in a lawn, and I never fertilize the lawn or the trees, so I don't think the issue is excessive nitrogen. Both trees get the same amount of sunlight: ample in the morning, then starting to get a little late afternoon shade. The last two years, the Bartlett has set a spectacular amount of fruit, so I think the basic conditions for pears are good here (Sacramento).