Gadenin日本語Get the appWhy one pear tree on its own usually fails
Most pears are self-incompatible: their own pollen lands on their own stigma, starts to grow, and is then shut down by the tree before it reaches the ovule. A lone tree can therefore flower magnificently every spring and set nothing, or set a handful of small misshapen fruit with no seed inside. A few varieties are described as partly self-fertile, which means they will set a light crop alone and a proper one with a partner.
The cure is another pear of a different variety, flowering at the same time, within about sixty feet (18 m). A second tree of the same variety is no help at all: clones share the same incompatibility, so two trees propagated from the same parent are, genetically, one tree. Neither will a quince or an apple do the job; they are different species and their pollen is rejected.
If you have no room for a second tree, graft a branch of a compatible variety into the framework of the one you have, or stand a potted flowering pear beside it during bloom. A single branch of a partner high in the canopy will pollinate the whole tree.
Flowering groups: overlap is the whole point
Pears are sorted into flowering groups, usually numbered one to four or five, where group one is earliest and each step is roughly five to seven days later. A tree pollinates any tree in its own group and, in most seasons, anything in the group immediately either side, because bloom periods are ten to fourteen days long and adjacent groups overlap by several days.
Two groups apart is a gamble that fails in a fast spring. When warm weather arrives suddenly, everything blooms closer together and you get away with it; in a cool, drawn-out spring the early tree has dropped its petals before the late one opens. Plan for the bad spring, not the good one.
A separate problem catches people out: a small number of pear varieties are triploid, carrying three sets of chromosomes instead of two. Their pollen is sterile. A triploid needs a partner to fruit but cannot pollinate anything in return, so if you own one you need two other varieties in the planting, not one.
| Flowering group | Relative bloom time | Pollinated by | Notes |
|---|---|---|---|
| Group 1 | Earliest, highest frost risk | Groups 1 and 2 | Only worth planting on a warm wall or a frost-free slope |
| Group 2 | Early | Groups 1, 2 and 3 | Widest choice of partners in most collections |
| Group 3 | Mid-season, most varieties sit here | Groups 2, 3 and 4 | The safest group for a first tree |
| Group 4 | Late | Groups 3 and 4 | Useful where late frosts are the normal pattern |
| Triploid, any group | As per its group | Two other varieties in overlapping groups | Sterile pollen, gives nothing back |
Cold, wind and the shortage of insects
Pear blossom opens when the weather is still poor for flying insects. Honeybees do very little below 55F (13C), and in wind above about twelve miles per hour they stay in the hive. Bumblebees and solitary bees work in colder, duller conditions, which is why a garden with rough grass, a bee hotel and early flowers nearby sets pears more reliably than one with a mown lawn.
Pear nectar is also thin and low in sugar compared with the dandelions and flowering currants blooming at the same time, so bees will leave the tree for something better. You cannot change the nectar, but you can shelter the tree from wind, which both keeps insects working and stops the stigmas drying out before pollen germinates.
Pollen stays viable on an open flower for two to four days at cool temperatures. If your whole bloom period is cold, wet and windy, that window closes without a single visit and the petals fall on an empty tree. That is the usual answer to why a healthy, well-partnered pear gave nothing in a particular year.
Hand pollination and frost protection
When bloom coincides with a cold week, hand pollination pays. It takes ten minutes and it is the difference between a crop and none on a small tree.
Frost is the other half of the problem. Open pear blossom is killed at about 28F (-2C), and a young fruitlet already set is killed at 29F (-1.5C), slightly more tender than the flower it came from. Cut a suspect flower in half after a cold night: a black center means the ovary is dead and that flower will drop, whatever the petals look like.
- Collect pollen from the partner On a dry afternoon, pick two or three fully open flowers from the pollinating variety, or brush the anthers with a soft artist's brush until yellow dust shows on the bristles. Pollen from a flower that opened today is the most viable.
- Work the receiving flowers Touch the brush, or the picked flower's anthers, to the sticky central stigma of each flower on the tree you want to set. Move flower to flower and re-charge the brush every ten or so. Work the flowers that opened in the last day or two, not the tired ones.
- Repeat over the bloom period Flowers open in waves over ten to fourteen days, so one pass catches only part of the crop. Go over the tree every second or third dry day until petals start to fall.
- Cover on frost nights Throw row cover or an old sheet over a small or trained tree before dusk on any night forecast to reach 32F (0C), and take it off in the morning so insects can work. The cover holds ground heat under it and buys three or four degrees.
Record which trees were in full bloom on which days, and note every night that hit freezing during that window. After two seasons those notes tell you whether your problem is a missing partner, a mismatch in flowering groups, or simply frost, and each has a different fix.