Gadenin日本語Get the appApples cannot pollinate themselves
Apple flowers carry both pollen and ovules, but the tree rejects its own pollen before it can fertilize the ovules. This is self-incompatibility, and it is built into the species. It means a single apple tree, no matter how well grown, will flower magnificently and drop every flower a fortnight later. The petals fall, the little green ovaries yellow at the base, and the whole lot is on the ground by early summer.
For fruit you need pollen from a genetically different apple tree, carried by bees. Another tree of the same variety is no help at all: every tree of a named variety is a graft off the same original plant, so a row of ten identical trees is, as far as pollination goes, one tree.
A crab apple counts as a partner and is often the best one, because crab apples flower over a long period and shed enormous quantities of pollen. So does a neighbor's apple tree, or a wild seedling in a hedge. Before you conclude you have a pollination problem, walk round the area at blossom time and look.
Flowering groups and the overlap you need
Varieties are sorted into flowering groups, usually numbered from earliest to latest. The group number does not say when the tree flowers in your garden; it says where it sits in the sequence relative to other apples. In a warm spring the whole sequence compresses, in a cold one it stretches out, but the order stays the same.
Two trees pollinate each other if their bloom periods overlap. That means the same group, or one group either side. Two groups apart is a gamble that fails in the years when spring comes quickly and the early tree is finishing as the late one starts.
Bloom on a single tree lasts about seven to ten days, longer in cool weather. The king bloom, the first and largest flower in the center of each cluster, opens a day or two ahead of the rest and produces the biggest fruit, so an overlap that only catches the tail end of one tree costs you the best apples.
| Your tree's group | Best partners | Workable | Will not overlap |
|---|---|---|---|
| Very early | Very early, early | Mid | Late, very late |
| Early | Early, very early, mid | Mid-late | Very late |
| Mid | Mid, early, mid-late | Very early, late | Very late |
| Mid-late | Mid-late, mid, late | Early | Very early |
| Late | Late, mid-late, very late | Mid | Very early, early |
If you do not know your tree's group, record the date the first flowers open and the date the last petals fall, for two years running. Two seasons of your own observations beat any published table for your own garden.
Triploids and other trees that give nothing back
Some apple varieties are triploid: they carry three sets of chromosomes instead of two, and their pollen is effectively sterile. A triploid tree will set fruit if it receives good pollen, but it gives nothing to its neighbors. Plant one alongside a single partner and you end up with a triploid that crops and a partner that does not.
The rule is that a triploid needs two other compatible trees in overlapping bloom, which then pollinate each other as well. If your one-partner arrangement produces a heavy crop on one tree and almost nothing on the other, a triploid is the first thing to suspect.
There is a second, rarer case: a few pairs of varieties share a common parent and are incompatible with each other despite flowering together. If two trees flower simultaneously, look healthy and both set poorly year after year, adding a third unrelated tree or a crab apple resolves it.
Getting the bees to actually do the work
Pollen does not travel far on the wind; apples depend almost entirely on insects. Bees fly when it is above about 55F (13C), dry and not blowing hard. A cold, wet or windy bloom period is enough on its own to wreck a crop even with perfect partners planted twenty feet apart.
You cannot control the weather, but you can control the rest. Do not spray insecticide on or near open blossom, at any time of day, for any reason. Leave dandelions and other early flowers in the grass under the tree, because they hold a bee population in the area before the apple opens. Site trees out of the worst of the wind, and keep the two partners in sight of each other rather than at opposite ends of the property.
Bees also work a tree far better when it is not crowded by taller trees. A tree in a sheltered sunny corner will be visited through more hours of the day than an identical tree on a cold, shaded side.
| Condition at bloom | Effect on set | What you can do |
|---|---|---|
| Cold, below 55F (13C) | Bees barely fly; poor set | Hand pollinate the king blooms |
| Rain through most of bloom | Pollen washed off; poor set | Hand pollinate on any dry hour |
| Strong wind | Bees grounded | Shelter or windbreak for future years |
| Frost at 28F (-2C) or below | Flowers killed outright | Cover small trees overnight with row cover |
| Warm, dry, still | Full set; expect to thin heavily | Plan thinning within a month |
Hand pollinating when the weather is against you
Hand pollination is worth doing on a young or small tree, or in a spring where bees simply have not flown. You are not trying to do the whole tree; concentrate on the king blooms, which give the largest apples anyway.
- Collect pollen from the partner On a dry morning after the dew has gone, pick a few freshly opened flowers from the partner tree, or brush their anthers with a soft artist's brush. Pollen is only shed for a day or two after the flower opens, so use fresh ones.
- Work the flower directly Touch the brush, or the picked flower's anthers, onto the stigmas at the center of each king bloom. Aim to visit the same flower on two different days, because the stigmas stay receptive for several days and are not equally receptive on the first.
- Do it in the morning Mid morning, once any moisture has dried off, is when pollen is loose and stigmas are sticky. Wet pollen will not transfer, and pollen collected in the rain is wasted.
- Stand a flowering crab next to the tree A potted crab apple in flower, moved beside the tree for its bloom period, is the low-effort version of the same thing and covers the whole tree rather than the flowers you can reach.
Do not strip the partner tree of its blossom to collect pollen. A dozen flowers is plenty; the anthers on a single flower carry enough pollen for several apples.
Reading the drop, and what to record
After petal fall, a tree drops fruitlets twice. The first drop, within two or three weeks, is the unpollinated flowers going; this is normal and can be most of them. The second, several weeks later, is the tree shedding what it cannot carry, and it happens even on a well-pollinated tree. Do not judge your pollination until the second drop has finished.
Cut a dropped fruitlet in half across the middle and look at the seeds. Plump, dark seeds mean it was fertilized and the tree let it go for other reasons. Flat white unformed seeds mean it was never pollinated at all. A whole tree of flat seeds is a pollination problem; a mixture is normal.
Each season, note the date the first blossom opened, the date of full bloom, whether frost hit and at what temperature, the weather across the bloom week, and roughly what proportion held. After three years that record tells you whether your partner really overlaps, or whether you have been lucky in warm springs and blank in cold ones.