Fruit Trees and Pollination
Many fruit trees require a pollinator, but what does that mean exactly? Although there are fruit trees out there that are self fruitful (like some cherry tree varieties for example), others will require a recommended pollinator to produce fruit (like apple trees).
Basically, the pollen is created from the flowers that bloom on the fruit trees. The pollen is carried from one type of tree to the next by insects, wind, etc. The cross-pollination that occurs is what allows non-self fruitful trees produce fruit.
The trees have to be the same species. So you will need an apple tree to pollinate another apple tree, or a cherry tree to pollinate another cherry tree (a cherry tree will not pollinate an apple tree). In order for pollination to take place, you will want two trees that have similar bloom times. If the trees bloom at different times, the pollen from one tree might not be produced at the correct time for the other tree to receive it.
If you are interested in growing fruit trees, you will want to find out if a pollinator is needed. If one is required for the type of tree that you are interested in, you will want to find another variety that is compatible.
If you are having trouble finding out which trees are compatible, try checking with an arborist or your local county extension agency. If you have a local university with a horticulture department, that is another good place to check. You may even try doing an internet search. There are several universities that post their pollination charts on the web.