Fruit Tree Pollination Groups: Why You Need Two Trees

Buy one apple or pear tree expecting fruit and you may get blossom and nothing else. Most apples and pears need a compatible partner flowering at the same time, while most plums and acid cherries crop on their own, so the rules differ by fruit. For a single tree, choose a self-fertileA plant that can set fruit using its own pollen, without needing a second, different variety nearby to cross-pollinate it. Full definition → plum such as Victoria or Czar, an acid cherry such as Morello, or a self-fertile sweet cherry such as Stella. Conference is the one pear that sets fruit without pollination.

Apples have their own numbered flowering-group system, set out in the apple growing guide. Where a numbered group applies at all, it is a rough bloom-timing band: varieties in the same or a neighbouring group flower closely enough together for insects to move pollen between them, and a variety three or more groups away is likely to have finished or not yet started flowering. Even self-fertile varieties tend to crop better with another variety planted nearby. Bees can fly 3 to 4km, but for cross-pollinationPollen moving from one plant to a different, compatible variety, needed for fruit to set on any variety that isn't self-fertile. Full definition → the usual rule is to keep trees within 18m (55ft) of each other. A neighbour's tree can count, and crab apples are particularly useful pollinators for apples because they flower abundantly over a long period.

Pears: apples' numbering, with more exceptions

Pears use the same numbered flowering-group system as apples. Most need a different pear variety flowering at the same time nearby to set fruit, so check whether a neighbouring garden already has a compatible pear before assuming you need a second tree. Conference, in Group 3, can set fruit without being pollinated, though it still fruits more heavily with a partner nearby. Beyond that, plan on a second variety from the same or an adjacent group:

A triploid produces mostly sterile pollen, so it can't pollinate another tree, and it needs two other compatible trees flowering at the same time to be pollinated itself. The pear examples are Merton Pride and the culinary pear Catillac.

Pears flower significantly earlier than apples, so their blossom is at greater risk from late frost, and they crop best in a warm, sunny, sheltered position protected from late frosts. In colder regions, which include much of Scotland, choose a variety that ripens early. Pears train well against a wall or fence as cordonsA fruit tree or bush trained as a single main stem with short fruiting side-spurs, usually grown at an angle against a wall, fence or wire. Full definition →, espaliers or fans, and a wall gives the warmth they want.

Plums: self-fertility is the default

Plums flip the pattern. Victoria, Czar, Opal, Blue Tit, Marjorie's Seedling, Belle de Louvain, Pershore, Warwickshire Drooper, Imperial Gage and Oullins Gage are all self-fertile, so one tree is normal, though it is worth checking the specific variety before buying. Cambridge Gage is only partly self-fertile, but that can still give a decent crop. Jefferson gage is self-incompatible and needs a partner. Among damsons, Farleigh and Prune Damson are both self-fertile.

For varieties that do need a partner, gages and damsons cross freely with plums as one broad family rather than sitting in a separately numbered system, so any nearby plum in flower at the right time will generally do. With plums the first question is whether the variety is self-fertile, not which group it belongs to. A second variety flowering at a similar time can still help a self-fertile plum crop more heavily, as an improvement rather than a requirement.

Plum blossom opens early, in March or April, and frost is a bigger practical risk than finding a partner. An early cold snap can wipe out a season's flowers however well two trees are paired. For colder areas such as Scotland, the late-flowering Blue Tit is recommended to reduce the risk of frost damage, and Pershore and Czar are named as more frost-tolerant, so choose one of these three on a site prone to a late cold snap. Train the tree against a south-, south-west or west-facing wall or fence for warmth and shelter, avoid frost pocketsA low-lying spot where cold air drains and pools on still nights, making it noticeably more frost-prone than the surrounding area. Full definition →, and avoid sites prone to heavy frosts or strong winds, which can damage blossom and deter pollinators.

Cherries: split by type, not by number

Cherries split into sweet cherries (Prunus avium) and acid cherries (Prunus cerasus), and pollination advice follows that split rather than numbered flowering groups. Acid cherries are self-fertile, so one tree is enough: Morello, the traditional acid cherry, needs no partner and tolerates partial shade, useful where the only free spot isn't in full sun. Sweet cherries need a sunny spot, and the variety matters more than anything else. Stella, Lapins and Sweetheart are self-fertile. Kordia and Summer Sun are not: they need a partner flowering at the same time, and pairing either with a self-fertile variety such as Stella, chosen so its bloom overlaps, is the practical fix. If you only have room for one sweet cherry, buy a self-fertile variety. Cherry blossom is vulnerable to frost too, so choose a sheltered site and cover small trees with fleeceA lightweight, breathable fabric laid or draped over plants to trap a little warmth and keep off frost, wind and some flying pests. Full definition → when frost is forecast.

Where Scotland's climate matters

The self-fertility lists and group numbers don't change north of the border. What changes is how forgiving the system is. Cross-pollination depends on insects flying between two compatible trees while both are in flower, and a colder, wetter spell gives them fewer good flying hours than a milder spring further south. That is a reasonable extra argument for a self-fertile variety where there's room for only one tree: it still needs pollen moved within its own flowers, but it isn't relying on a second tree flowering in step with it.

Late frost at blossom time is a separate risk that a pollination partnerA second, different variety of the same fruit planted nearby so the two can cross-pollinate each other, needed by any variety that isn't self-fertile. Full definition → does nothing to solve. Choosing a frost-tolerant or late-flowering variety, siting the tree on a sheltered wall away from a frost pocket, keeping the grass short around it in flower (long grass stops heat radiating from the soil) and covering blossom with fleece or hessian on frosty nights are the real defences. On a wall-trained tree, use two or three layers of horticultural fleece, hessian or shade netting, rolled up in daylight so insects can reach the flowers, and kept ready for up to two weeks after flowering if hard frosts threaten.

What to do

One tree, no compromise on cropping: a self-fertile plum (Victoria, Czar, or Blue Tit for a cold site), or a self-fertile cherry, sweet (Stella, Lapins) or acid (Morello). One pear: Conference is the exception that fruits without a partner, though a second tree still helps. One apple: only specific self-fertile varieties crop reliably alone; the apple growing guide covers which, and the triploid trap.

Two trees needed, no way round it: most apples, most pears (bar Conference), Jefferson gage, and sweet cherries such as Kordia or Summer Sun. Match flowering group or timing, and for a triploid remember it needs two other compatible trees, not one. Room for only one hole: a family tree, with two or three compatible varieties graftedJoining a chosen fruiting variety onto a separate rootstock, so the tree grows the fruit of one plant on the roots of another. Full definition → onto one rootstockThe root system and lower stem a fruit tree is grafted onto, chosen to control the tree's eventual size rather than for its own fruit. Full definition →, solves it directly, and a dwarfing rootstock keeps two trees small enough to fit; see the fruit tree rootstocks article. A neighbour's tree nearby: worth checking, for pears especially, before planting a second.

For growing detail beyond pollination, see the pear, plum and cherry growing guides.

Common questions

Sources