Importance of pollination
Most apple varieties are not self-fertile, and will not set a full crop of fruit without a compatible polliniser, particularly if flowering is sparse, or weather conditions are adverse. Even varieties that do have some self-compatibility will produce a much better crop with a different variety acting as a polliniser.
Successful pollination, and the formation of many healthy seeds within the fruit contribute to the eventual size and quality of that fruit. Poor pollination results in reduced yield and misshapen fruit. Consequently, when planning a new apple block it is important to include a suitable polliniser variety.
Commercial varieties can make suitable pollinisers if they have compatible pollen and good flowering overlap. Crab apples can also be considered as pollinisers, particularly where a second variety is not desired, or the use of another variety will make complicate orchard management.
Successful cross-pollination depends on several factors, all of which need to be considered when designing and managing an orchard.