Apple Pollination
Most apple varieties require another variety for pollination. Generally, all you need to worry about is the overlapping of bloom times. If both apples are in bloom at about the same time, then the bees can do their job carrying pollen from each one to the other. Early bloomers and mid-season bloomers work fine with each other. And late season bloomers also work fine with mid-season bloomers. But don't count of early season bloomers and late season bloomers to pollinate each other – most years, they will not be in bloom at the same time. And, of course, planting three varieties - early, mid, and late - will cover all of the bases.
As mentioned above, there are some exceptions. First, a few apples are self-pollinating. These include Golden Delicious, Jonathan, Red Rome and Newtown Pippin. But bear in mind that even self-pollinating apples will produce a lot more fruit if it has another apple to provide pollen. All commercial orchards always plant pollinators with self-pollinating varieties to maximize their production.
A few apples are pollen sterile. Gravenstein, Stayman and Winesap fall into this category. This means that while they need to be pollinated by another variety, their pollen is sterile and will not return the favor. So you need to plant two other apples with a pollen sterile variety, so that all three will get pollinated.
