The following is paraphrased from an excellent, witty book on fruit growing (I think long out of print) by Raymond Bush: Tree Fruit growing, volume 2, 1949, published by Penguin.
If you have a preference for a particular variety and wish to plant your orchard to that variety, the minimum number of trees of another suitable type to ensure adequate pollination must not be less than eight to one. Thus you may have eight Cox's Orange Pippins to one James Grieve or Egremont Russet, or other suitable variety. The planting layout should be as follows (C=Cox, P=Pollinator):
C C C C C C C C C
You can see from this diagram that every main variety faces the pollinator:
C C C
Pollination is a curious business. The act of depositing pollen from another variety onto the receptive stigma of the blossom is purely incidental to the bee's work. The pollen usually adheres to the furry abdomen of the forager and is brushed off on to the stigma. Once there, fertile pollen grains send down germ tubes like tenuous roots via the styles into the pip pockets, where the embryo pip is energised into action, this in turn causing the pulp around the pip to swell and grow. Honey bees tend to stick to a single species of flower# when collecting nectar or pollen, so fertilising self-sterile fruits would be a very chancy business were it not for the fact that bumble bees are less particular. As it is, only one bloom in twenty is needed to set a full crop if the blossom is good.
In choosing a variety or varieties to
plant as pollinators you need the flowering periods to
coincide. Usually there is some overlap in the
flowering period, but since suitable pollinating
weather in a bad season may only last a few hours
(one might even say minutes in a really bad year)
the variation in bloom period should not be pronounced.
In such seasons, hand pollination may be very useful.
Nigel Deacon / Diversity website
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