It has been known for many decades that partially girdling (or ringing) the trunks of apple trees can increase the numbers of flowers produced in the subsequent season.
- The girdling treatments may comprise a single narrow diameter knife cut, made through the bark into the cambium of the tree for the whole circumference of the trunk.
- Alternatively, it may comprise two slightly wider cuts, usually made one slightly above the other on each side of the tree each for half of the trunk circumference.
Trials at East Malling over the years have shown variable effects of partial girdling (bark ringing) on the subsequent vigour of extension shoot growth.
- Whilst growth is reduced in some trials, in others it is not.
- However, in most trials flowering abundance has been improved following girdling.
- Research in the USA showed that girdling six-year-old trees of the tip bearing variety Cortland 19 days after full bloom increased flowering in the subsequent season but had no effect in the season after that (Greene and Lord, 1983).
- Where trees have become unbalanced, in terms of their excessive shoot growth and poor flowering, girdling (bark ringing) of the trunk may provide a means of improving floral abundance and reducing excessive shoot growth.
- However, this is not a reliable technique and the use of growth regulators and/or root pruning should be used in preference.
- Care must be taken, however, when bark ringing varieties which are sensitive to diseases such as apple canker (Nectria galligena).