Most sites benefit from planting strategically positioned living windbreaks or the erection of artificial windbreaks. These reduce the speed of wind flows across the site in the spring, so reducing the desiccating and chilling influence on the delicate and vulnerable floral organs. Improved shelter and the associated reduced wind speed and higher temperature also encourage the activity of the essential pollinating insects.
Living windbreaks should ideally be established several years ahead of planting the orchard if the early yields on young trees, that are vital to orchard profitability, are to be secured. When planting living windbreaks, it is recommended that deciduous species, which compete strongly for water and nutrients, such as willow (Salix) and some types of poplar (Populus), are avoided.
- Alders are one of the best genera for use as windbreaks in apple orchards and Alnus cordata and Alnus incana are especially suited to the purpose.
- Windbreak trees are generally planted in single rows with plants spaced 1.0 to 1.75m apart.
- In particularly exposed locations, a double row of trees may be warranted, with the rows spaced 2m apart.
Evergreen species are occasionally included as a proportion of the trees in a windbreak.
- These may be of value where the main windbreak species is particularly slow to leaf out in the spring when the protection for flowers is most critical.
- However, windbreaks made up entirely of evergreen species (e.g. Chamaecyparis spp) are, like very dense deciduous windbreaks, not to be recommended.
- This is because they cause excessive air turbulence both up and down wind of the windbreak.
Artificial windbreaks, made from plastic netting on poles and wire, are only rarely used in UK orchards.
- They are relatively expensive and have a limited lifespan.
- However, in the absence of living windbreaks or where the latter are too young to provide adequate shelter to young trees, they can be of transient value.
It has always been recommended that windbreaks are planted/erected at approximately 100m intervals around and across level orchard sites so as to provide adequate shelter for pollination, but not impede the escape of cold air flows.
- They should be kept regularly trimmed and may be allowed to grow to approximately 7m in height.
- A well-managed windbreak will provide maximum shelter for a distance of approximately 5 times its height, but some reduced shelter will be achieved up to a distance of 20 times its height.
- On sloping sites, with windbreaks grown across the slope, the base of the windbreak must be kept free of vegetation for a height of 1.5 to 2.0m to allow the unimpeded escape of cold air down the slope in the spring and avoid the creation of mini frost pockets.
- Choose species such as alders or hornbeam, which are less competitive for water and nutrients than willows or poplars.
- Plant at spacings of 1.0 to1.75m apart in single or, if very good shelter is needed, in double rows. Irrigation and fertigation will improve establishment.
- Trim windbreaks regularly and cut to approximately 7m in height.
- Plant windbreaks in advance of planting the orchard trees to ensure adequate shelter when the young apple trees begin to flower.
Where living windbreaks are not available use artificial windbreaks.