At the upper side of the branch is a slightly raised ridge of bark – the branch bark ridge. This marks the end of branch tissue and the beginning of trunk tissue.
As a branch begins to wane the tree forms a protective layer in the wood at the base of the branch – the branch collar.
Pruning cuts should always be just to the branch side of the branch bark ridge and branch collar (when one exists), downwards and slightly outwards. If the branch bark ridge or branch collar are damaged or removed, for instance by cutting flush to the trunk, not only is the main stem damaged, but the tree’s internal chemical protective layer is also removed. This allows disease and decay organisms to enter the wood.
Flush cuts may also result in cracking of the timber.
Long stubs should not be left as decay infecting them will easily find its way into the heartwood.
The best time to prune is at the end of the dormant period (late winter/early spring) so that a callus will start to form almost immediately, leaving less time for infection. Avoid pruning when the leaves are expanding.
Exceptions are:
- Hornbeam, birch, maple – prune October/November
- Walnut – prune in summer
- Cherry – prune June/July
Painting the wound will have little beneficial effect and may even encourage the spread of infection. If painting is desirable for cosmetic reasons a thin coat of commercial material is best. Household paints should not be used.
All these points apply to broadleaves and conifers, to live, dying or dead branches. The same procedures should be used for removing small branches from larger ones.
In brief:
- Never damage the branch bark ridge or branch collar
- Don’t cut flush to the trunk
- Don’t leave stubs
- Prune at the end of the dormant season
- Avoid painting the wound
