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 Pollination of apple trees and other fruit trees

Pollination is an important topic when growing fruit trees because many - but certainly not all - varieties require pollination from a compatible donor tree before they can set fruit.

Pollination appears (and probably is) a very complicated subject. However don't let this put you off - it is a natural process that almost always "just works". Some simple rules of thumb:

  • If you are in an urban environment you probably won't need to worry about a pollination partner for your apple tree - there will usually be compatible apple trees in neighbouring gardens and hedgerows. Pears, plums, and cherries are a bit less widely-planted though, and you can't assume there will be others nearby, but try asking around.

  • For varieties which are not self-fertile, and require a pollination partner, the partner has to be a different variety of the same fruit species. Two trees of the same variety will not pollinate each other.

  • If you are in an isolated area and only want to plant one tree, choose a self-fertile variety.

  • If in doubt, and you have space for more than one tree of the same species (e.g. 2 apple trees or 2 plum trees), plant two compatible varieties. (If doing so, it is a good idea to choose varieties that have different picking times so that you have a spread of fruit through the season).

So having reassured you that pollination is not such a big issue when choosing what fruit trees to grow, here are some of the factors that can affect pollination:

Species

In general terms each species can only pollinate others of its own kind - apples will only pollinate other apples, pears will only pollinate pears, and so on.

Amongst apples there is generally no distinction between crab apples, cider apples, and mainstream apples - they can all potentially cross-pollinate each other.

Things are less clear with plums. European plums (Prunus domestica) can inter-pollinate with closely-related species such as damsons, mirabelles and cherry plums. European plums cannot generally cross-pollinate with Japanese plums (Prunus salicina).

Sweet and Acid cherries are also different species but can potentially cross-pollinate each other.

Blossom time

For most fruit varieties, pollination is carried out by insects, often bees. Since pollination happens in early spring, good weather which will encourage bees is a factor. In the UK and other cool temperate climates a common problem with species such as apricots and peaches is that the blossom appears extremely early, before pollinating insects are about. (Even though apricots are self-fertile and do not need a separate pollination partner, the blossom still needs to be pollinated so lack of insect pollinators can be a problem).

Pollination also depends on having blossom to be pollinated - which is why the risk of late frosts which can damage blossom is sometimes a factor. Frosts just after pollination can also damage the first stages of fruit formation.

Flowering groups / Pollination groups

One of the easiest and simplest ways to see if two varieties could pollinate each other is to check their pollination or flowering groups. The flowering groups are not the only factor in determining compatibility between varieties, but they are the main starting point.

This works for apples, pears, and most plums and pollination is most likely to be successful with two varieties that are in the same group. These groups are somewhat arbitrary but the concept is simple - each group contains varieties that flower at around the same time. Groups may be given letters or numbers, but they typically run from the earliest-flowering to the latest-flowering varieties in each species.

Varieties in neighbouring groups will also work fairly well because the groups overlap in time. Our variety pages automatically show you compatible varieties based on these flowering groups.

Blossom day - best avoided

Some authorities record precise dates for the peak blossom day of each variety. This sounds more accurate than flowering groups but in practice this data is not much use and is potentially misleading.

The problem is that flowering dates are different from one region to another i.e. trees in more southerly or sheltered regions will usually start blossoming earlier than those in more northerly climates.

The seasons are also different from one year to the next, depending on the severity of the winter and the weather during spring. The unusually hard winter followed by an unusually mild spring of 2011 in the UK advanced blossom by as much as 4 weeks for some varieties.

A more subtle point is that in continental climates such as much of the USA, spring is often compressed - the transition from winter to summer happens very quickly. In contrast in temperate climates such as the UK - where much of the original blossom data was first recorded - the transition is much slower, with the result that the blossom season is relatively longer.

For all these reasons, knowing an exact day can be misleading. The flowering groups, by virtue of being less precise, are more helpful when comparing different varieties.

Rootstocks and flowering groups

Another complication is that the rootstock can affect the flowering times. For example, any apple variety grafted on the MM106 rootstock will tend to flower a few days ahead of the same variety on most other apple rootstocks, whilst the M9 and M25 rootstocks tend to delay flowering by a few days.

Good pollinators and poor pollinators

Some varieties naturally tend to produce a lot of blossom over a long period, and/or are genetically highly compatible with a lot of other varieties - this makes them good pollinators for other varieties. Most crab apples fall into this category and commercial apple orchards sometimes inter-plant them for this purpose.

Some varieties are very poor pollinators. Bramley's Seedling is a particular case in point, because it is a 'triploid' variety which means not only does it require 2 separate pollination partners, but its own pollen is ineffective at pollinating other varieties.

Self-fertility

Most apple varieties are self-infertile but there are a few exceptions such as Red Windsor / Alkmene which are self-fertile - they do not require a pollination partner. However, fruiting is usually improved with a suitable partner.

In other species such as apricots, peaches, nectarines, the rule is the opposite - they are invariably self-fertile so you can safely plant just one example. However even self-fertile varieties still need the pollen to be transferred from one flower to a neighbouring flower and if bad weather deters pollinating insects the pollination may be poor and you will get a reduced "fruit set".

Relationships

Even if all the other factors are taken care of, sometimes varieties are still not compatible. This is often because there is a family relationship. Thus Golden Delicious - which is an excellent pollinator for many apples because of the duration and quantity of blossom - will not pollinate Jonagold or Crispin and is a poor pollinator of Gala, mainly because these varieties are closely related to it (very closely related in the case of Jonagold and Crispin).

These relationship incompatibilities operate at a genetic level and are therefore difficult for the non-scientist to find out about. However a useful rule of thumb is that you can usually assume traditional varieties from the USA are unlikely to be related to traditional varieties from Europe and vice versa. Thus Golden Delicious is a good pollinator for many heirloom European varieties. This rule breaks down for varieties developed from the late 19th century onwards though, because by then transport and communication links had developed and new varieties were increasingly raised by research stations and knowledgeable amateurs using varieties from both continents.

This self-incompatibility is a particularly important issue with the pollination of sweet cherries, and very complicated to work out. For this reason it is often best to plant a self-fertile sweet cherry.

Fruit bud formation

In order to have pollination you have to have blossom ... and in order to have blossom some of the buds must be fruiting buds rather than leaf buds. Perhaps surprisingly, this year's fruit buds are formed the previous summer. Therefore if you have good spring weather but little blossom, the cause is often incorrect pruning the preceding summer.

Conversely, you can encourage a tree that is not producing much blossom to create more fruit buds by tying new branches to the horizontal in early summer - this fools the tree into thinking that it is fruiting, and in turn causes it to set new fruit buds (which will hopefully blossom next spring).

Check apple tree pollination compatibility online

This ON-LINE POLLINATION CHECKER takes into account all the above factors and can suggest pollination partners for a large number of different apple varieties.

Final word

As we said at the top of the page, in spite of all the apparent difficulties, pollination is rarely an issue in practice.