Some varieties set no fruit at all when self-pollinated, while others under favorable conditions set a fair crop.
Yields are better when there are enough varieties for cross-pollination.
It is important to have at least two diploid varieties in a collection, unless the pollinator chosen is sufficiently self-fertile alone. When choosing varieties select those which will flower about the same time or overlap by a few days with others. There is some variation in the flowering periods of varieties but on the whole the times are very consistent. Winter temperatures and district can affect flowering periods. In the following tables varieties are in seven flowering groups.