In order to produce fruit all fruit trees must be pollinated.
When choosing a fruit tree one of the most important characteristics is therefore whether the variety is self-fertile, partially self-fertile, or self-sterile.
Such varieties are classified as Although the rootstock is the main influence on the mature height of a variety, the variety itself may be more or less vigorous relative to others.
Weak varieties are not necessarily less desirable than vigorous ones - all have their uses.
The groups are always relative to the fruit species - plums for example bloom much earlier than apples, but within plums some will be early and some will be late bloomers.
Flowering groups are a useful guide to pollination compatibility but there are many exceptions - these are covered in our individual variety pages.
Unlike spur-bearers, which need maintenance pruning as the tree gets older, tip-bearers generally should not be pruned, as doing so would prevent them fruiting.
In the case of plums, many important varieties are self-fertile, but many are not.
Don't let this put you off triploids though - their extra chromosome often makes them bigger, more productive, and more disease-resistant.
Some varieties naturally produce larger than usual quantities of pollen, and/or produce pollen over a longer period than usual, and/or are genetically compatible with many other varieties.
With cherries, most (but not all) modern sweet cherries are self-fertile.
Most of the traditional varieties are self-sterile.