How many trees do I need for pollination?
Do I need two trees for pollination?
That depends on the species! Almost every apple and pear, for example, requires two different varieties to be planted near each other in order for them to cross-pollinate and produce fruit. These trees generally need to be the same species, so an apple will not pollinate a pear and vice versa.
If you check the description of each fruit, it will say whether it needs a pollinator, is partially self-pollinating, or is self-pollinating. Partially self-pollinating trees will produce some fruit by themselves but likely not very much and self-pollinating fruits will produce a decent crop on their own.
Generally, even self-pollinating trees produce more and better fruit if planted with a tree of a different variety that blooms around the same time.
Why do I need two different varieties for pollination?
For apples and pears especially, different trees of the same variety are unable to pollinate each other because they are genetically identical as grafting is like a cloning process. The blooms will simply not accept the pollen from another tree of the same variety for this reason, so two varieties must be planted to introduce new genetic material.
What does triploid mean and why does it need more pollinators?
Some of our apple trees are triploid which means they have sterile pollen. This means that they can be pollinated by another variety but they cannot pollinate other trees. In order for the non-triploid tree to be pollinated, a third non-triploid variety will need to be planted.