Tempted by the idea of growing your own fruits? It can be very rewarding and is not all that difficult, but… you first have to have some inkling of the curious sex habits of fruit trees and small fruits.
It Takes Two to Tango
Cross-pollination is mandatory for the vast majority of temperate-climate fruits including apples and blueberries, as well as most plum, cherry and pear trees. These plants are “self-sterile”, that is to say, their pollen won’t fertilize their own flowers and they therefore need another compatible variety for cross-pollination in order to produce fruit. For example, the pollen from a ‘Liberty’ apple tree can’t fertilize the flowers of the same tree or of any other ‘Liberty’. However, if you plant a different cultivar nearby, in fact, pretty much any apple cultivar (‘Novamac’, ‘Priscilla’, ‘Macfree’, etc.), it will pollinate a ‘Liberty’ apple, allowing it to produce abundant fruit. So for easy fruit production, the simple solution is to always plant two or more cultivars of any fruit tree. Of course, the pollen must come from a closely related plant. All cultivated apples (Malus domestica) are very close relatives and can cross-pollinate. Note too that crabapples are also apples, just small-fruited ones, and they too can pollinate apple trees. That’s why, in many suburbs where crabapples are commonly planted, it is not always necessary to plant a second apple tree for an abundant harvest: bees will simply carry the needed pollen from a neighboring crabapple.
But the trees have to be really close relatives to cross-pollinate. Although pears (Pyrus spp.) are related to apples, their pollen will not fertilize the flowers of an apple tree, or vice versa. However, as with apples, most pears (Pyrus communis) are self-sterile and must be pollinated by another pear.
In the case of plum and cherry trees (both are in the genus Prunus), the situation is more complex: again, most are self-sterile, but in general they need plants of the same species for pollination to occur, not just the same genus.
Take plums, for example. There are three main types used in home gardens. European plums (Prunus domestica) can pollinate other European plums, Japanese plums (P. salicina) can pollinate other Japanese plums and American plums (P. nigra and P. americana) can pollinate other American plums. But just to complicate things even more, some American plums can pollinate certain European and Japanese plums! I suggest just ignoring that fact: just plant plums of the same species and you’ll always get good pollination.
Things are simpler with cherries: sweet cherries (Prunus avium) pollinate sweet cherries, sour cherries (P. cerasus) pollinate sour cherries, and just about any other cherry (and there are dozens of species!) will pollinate cherries of its own species, but not others.
As for blueberries (Vaccinium angustifolium, V. corymbosum and others), they are mostly self-sterile so you need at least two varieties of the same species for good fruit production. (Different species can sometimes cross-pollinate, at least in theory, but rarely flower at the same time, soooo…) In fact, most growers recommend you plant at least three varieties of the same species of blueberry to ensure a good crop each year.
Cross-pollination is Not Always Necessary
For some fruits, cross-pollination is not required: sour cherries (Prunus cerasus) and European plums (P. domestica) are self-fertile (their own pollen will fertilize their flowers) and you therefore don’t need two different trees for a good harvest.
This is also true of most peaches (P. persica) and nectarines, the latter simply being peaches without the fuzz, although there are a few self-sterile varieties of peaches and nectarines, that is varieties that will require a pollinator. Apricots (P. armeniaca) are a mixed bag: some are self-fertile, some are self-sterile.
Most small fruits, too, are self-fertile and therefore even an isolated plant will bear fruit. The main exceptions here are blueberries (Vaccinium spp., already mentioned), haskaps, also called honeyberries (Lonicera caerulea) and some blackberries (Rubus spp.): they all require the presence of another cultivar for good fruit production.
Partially Self-Fertile: Just to Make Things Complicated!
In most categories of fruits that are generally self-sterile, there are exceptions. You’ll see the mention “partially self-fertile” in the descriptions of these plants. It means they can self-pollinate… under the right conditions. This is notably the case of most Asian pear cultivars (Pyrus pyrifolia), some European pears (‘Flemish Beauty’, ‘Bartlett’, ‘Anjou’ and a few others) and some apples (‘Golden Delicious’, ‘Braeburn’, ‘Granny Smith’, etc.).
Before declaring victory, however, be forewarned that partially self-fertile varieties often produce fewer fruits when they are on their own. Yes, there will generally be some successful fertilization and even a few really good years, but most of these varieties still produce more faithfully if there is another variety nearby for cross-pollination. Thus, it is better to give these partially self-fertile varieties a partner if you want a good harvest every year.
If Space is at a Premium
If your favorite fruit requires a pollinator and you don’t have space for a second tree, here are two possible solutions:
1. While your tree is in bloom, cut a branch from a compatible variety (you’ll need a friend who cultivates one) and place it in a vase of water at the foot of your tree. Bees will ensure the pollen gets transferred.
2. Or better yet, graft a branch of a different variety (of the same species, of course, like apple on apple, pear on pear) onto your tree. That way your tree will have a pollinator on hand every spring!