Why Flowering Time Decides Your Crop

Every spring, fruit growers wait for blossom. But blossom alone guarantees nothing. Most apple, pear, plum and sweet cherry varieties cannot set a worthwhile crop with their own pollen. They need pollen from a different variety that flowers at the same time. Get that wrong and you can spend years wondering why a healthy, well-fed tree produces a handful of fruit and then drops it in June.

That is the whole point of pollination groups. They are simply a way of sorting varieties by when they flower, so you can pair trees that will be open at the same moment. Check compatibility before you order, not after the tree is planted.

How the Groups Work

Most UK fruit catalogues use letters or numbers. Apples and pears usually run from group 1 (earliest) to group 6 (latest); some nurseries use A to F instead. Cherries and plums are listed the same way, often with a smaller number of groups.

As a rough guide in a typical British season, group 1 apples open in early April, group 3 in late April to early May, and group 6 in late May. A fortnight of difference between the extremes is normal, though the gap shifts with region and weather.

The rule is straightforward: a variety pollinates another if they sit in the same group or in neighbouring groups. A group 3 tree will work with group 2, 3 or 4. It will not reliably work with group 1 or group 5, because the blossoms will barely overlap. Most growers aim for one group either side as a safety margin, since a cold spring can delay one tree and not another.

The Rules That Catch People Out

Compatible groups are only the start. Three details trip up even experienced gardeners.

• Triploids. Some of the best-known varieties, including Bramley's Seedling, Blenheim Orange and Ribston Pippin, carry three sets of chromosomes. They produce little or no viable pollen. They can be pollinated by a partner, but they cannot return the favour. If you plant a Bramley, you need two other varieties in compatible groups, not one.
• Self-fertile varieties. Some trees set fruit on their own pollen: most sour cherries such as Morello, many sweet cherries including Stella, and plums such as Czar and, to a degree, Victoria. Even these usually crop better with a partner nearby, so treat "self-fertile" as convenient rather than ideal.
• Same group, wrong partner. Two trees in group 3 are not automatically a match if one of them is triploid. Group numbers tell you about timing, not about pollen quality.

Matching Partners Before You Buy

Take five minutes with a nursery catalogue before you commit. Write down the variety you want, note its group and whether it is diploid, triploid or self-fertile, then choose a partner that overlaps.

As an example: Cox's Orange Pippin sits in group 3 and is self-sterile. Good partners include James Grieve, Katy or Egremont Russet, all of which flower at a similar time. Bramley's Seedling is also group 3, but because it is triploid it cannot serve as Cox's pollinator; plant a third variety if you want both.

For pears, Conference and Concorde are partially self-fertile and will often crop alone, but Comice benefits from a partner such as Williams' Bon Chrétien in an overlapping group. Sweet cherries are the least forgiving: assume you need two different varieties unless the label says self-fertile.

Small Gardens and Awkward Spaces

You do not need an orchard to get pollination right. A family tree, with two or three compatible varieties grafted onto one trunk, solves the problem in a single planting space. Choose varieties from the same or adjacent groups and check that any triploid on the tree is accompanied by two others.

Neighbours count too. A compatible tree within roughly 20 to 30 metres, ideally closer, will do the job — bees are happy to cross a hedge. Crab apples such as Golden Hornet flower over a long period and are excellent universal pollinators for apples, which makes them useful in a mixed garden. Ornamental cherries and plums are less reliable, as many are sterile or flower at the wrong time.

Helping the Bees Do Their Job

Compatible varieties still need insects to move the pollen. Honeybees generally fly only above about 10°C, and bumblebees a little cooler, so a cold, wet fortnight during blossom can cut your crop regardless of your planning.

• Plant in the sunniest, most sheltered spot you have; a warm wall can advance flowering slightly and speed up bee activity.
• Avoid spraying anything on open blossom, including organic controls, and let dandelions and other early flowers stand nearby.
• Watch for late frosts. If a hard frost is forecast when trees are in full flower, fleece what you can and accept that some early groups may lose their crop.
• Keep grass mown around trees during blossom so bees can find the flowers easily.

Get the group numbers right, plant for overlap, and the rest of orchard growing becomes far more forgiving. A little planning at the buying stage is the cheapest harvest insurance you will ever take out.