It is essential to plant sufficient numbers of trees of a pollinating variety within an orchard, to provide adequate quantities of viable pollen.
- There is no single ideal ratio of pollinating to main variety trees and no strong scientific evidence on which to make objective assessments.
- For the average situation ratios of 1:9 were traditionally recommended in the UK.
- Lower ratios of pollinator to main variety are recommended (e.g. 1 pollinating variety to 10 or more main variety trees) where:
- Pollinating varieties with high flower abundance and high pollen production (e.g. Golden Delicious) are chosen.
- The pollinating varieties are fully compatible with the main variety (see ‘Pollen compatibility’ section).
- The pollinating varieties flower at the same time as the main variety in most years.
- Orchard environmental conditions are favourable (shelter, aspect) for bee activity, pollen germination and rapid growth down the style.
- The type of tree grown and/or the site lead to the production of well-controlled growth.
- Where several of these criteria are not met the ratios should increase to 1:4 in the worst situations.
Bees tend to work down rows of trees rather than across them.
- Wherever possible the pollinating varieties should be positioned in every tree row rather than in one in two or one in three rows.
- This is less important in bed systems where trees in 2, 3 or more rows are in close proximity.
Another consideration is the maximum distance between the pollinating variety and the main variety. There is evidence to suggest that distances above 15 to 20 m are likely to result in reduced pollination efficiency (Mišić, 1994; Free and Spencer-Botth, 1964).
- More recent trials in the former Yugoslavia indicate that, whilst distance from the pollinating variety was important for Golden Delicious (fruit set and yield better at 5m than at >20m), for Jonathan there was no similar effect (Milutinović, et al., 1996).
- Trials undertaken in the Czech Republic showed that efficient pollination of the variety Golden Delicious was achieved with pollinators planted as far as 40 m away (Blažek, 1996).
- It is suggested that this is explained by honey bees making extended foraging trips on some occasions (Free and Durrant, 1966).
- The Czech author also suggests that better pollen mixing occurs when bee hives are located outside the orchard blocks rather than deeply within them.
- Trials in Hungary suggest that for high density systems trained to slender spindles on M.9 rootstock 10-15 metres is the maximum distance between trees of the main and pollinating varieties (Soltész, 1997).
Take advice from your local advisor before choosing a ratio of pollinator to main variety for planting in a new orchard. This ratio will be influenced by:
- How favourable the orchard location is, in terms of temperatures and shelter from winds.
- The populations of bees, either wild or introduced in the orchard.
- The pollen producing abilities of the pollinating varieties chosen.
- The propensity of the main commercial scion variety to set abundantly or lightly.
- The compatibility (full or partial) of the chosen pollinating varieties with the main variety.