Most people are not aware that some apple trees produce bad pollen. Unless you're careful, this means reduced yields of fruit.
Some apples set no fruit at all with their own pollen. Others set a small crop, but even those which set a good crop with their own pollen will set a better one if cross-pollinated. So if you plant a few trees, you need at least two sorts.
Some apple varieties have 34 chromosomes and are known as DIPLOID. These are self-fertile, have good pollen, and can often set good crops on their own. Some have 51 chromosomes (TRIPLOID) and because it's an odd number it affects fertility ... so the pollen is virtually useless, though it will sometimes pollinate itself to some extent.
Sometimes, you'll need TWO pollinators - to pollinate the triploid and each other so that the pollinators have good crops of their own.
I've noticed that most triploid apples are large, and I guess this might be linked to the high chromosome number. But from a practical point of view, all we need is a list of varieties, so here we go:
Belle de Boskoop
-so if you plant a single apple tree, and your neighbour has no trees, don't plant any of the above.
Note that some triploids will give a crop on their own, though it will usually be smaller than if cross-pollinated. There's another page on this site concerning the experiments of Crane and Lawrence, where they looked at the number of fruit per 100 blooms...it's worth reading.
Good pollinators which you might plant nearby (or which you might graft onto your triploid tree, if you only have room for one) are...well, virtually every apple variety not on the above list, plus crab apples. Crabs are very good pollinators and are often planted in commercial orchards for this purpose. When I went to see the thousands of spectacular trained apple trees in Versailles a couple of years ago there were crab apples at the end of each row.
There are a few apple trees with 68 chromosomes which are known as TETRAPLOID. Their pollen is good, but they are not often grown . A biologist friend tells me that the high chromosome number helps the fruit reach a good size in adverse conditions, so these might be the choice in a more northerly climate. I found one reference on the internet saying that they are often watery and misshapen, but I have no personal experience of them.
Nigel Deacon / Diversity website
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