Hydraulically-operated flail trimmers have superseded earlier cutter-bar machines, and are the standard method of cutting hedges and banks. Cutting heads of 4’ (1.2m) and 3’ (910mm) are available in various weights for cutting grass, woody growth up to 2” (50mm) diameter and woody growth up to 4” (100mm). Provided the correct head is used for the job, and the flail is properly maintained and the tractor is operated at a slow speed, a clean and tidy trim can be achieved. Hedge-cutting machines should only be used by suitably trained operators.
The hedge should be trimmed from the top downwards, so that fallen cut material is further cut and mulched as the flail head moves down the hedge. Within the limits of the space available and the size of the flail head, the hedge should be cut a little further out at each annual or biennial trim, with the result that it gradually expands in height and width. This will ensure that each trim produces plenty of vigorous, leafy growth. If it is cut to the same point at each trim, ‘bird’s nest’ growth (p84) will result. After about five successive trims the hedge should be cut back hard to its original dimensions.
Where the hedge is overgrown, with more than about 18” (450mm) to be removed, the growth should be cut back in stages, each of no more than 18” (450mm), with the flail head changed as necessary as growth becomes thicker in diameter. This gives a cleaner finish to the hedge, avoids overloading the cutting head, and produces short trimmings which rapidly decompose.
Shapesaw or sawhead cutters with a circular blade, mounted on a tractor arm, are used for heavy cutting work, including coppicing. The hedge should be cut in the opposite order to the procedure when using a flail, by starting with the outer and bottom growth, to allow the cuttings to fall clear of the hedge. The cut material must be gathered up for burning or chipping.
Common faults resulting from poor mechanical cutting are:
- ‘Buck-headed’ hedges. These occur where frequent light trimmings, each further out from the centre of the hedge than the last, result in a tall ‘leggy’ hedge which is thin and gappy at the base. The hedge should be cut hard back to encourage new growth from the base and from the cut stems.
- Undercut hedges. These result where verges and banks are cut too close to the centre of the hedge, removing growth at the most important part, which is the bottom 2’ (600mm).
- Very small hedges. Over enthusiastic tidying can reduce a hedge until it is so small as to be virtually useless.
The A-shaped or topped A-shaped hedge described above has several advantages for mechanical cutting operations.
- Cuttings fall off, and not into the hedge.
- Fewer passes of the machine are required than for a flat-topped hedge.
- There is less danger to the tractor driver as debris is directed downwards, and not towards the tractor cab.
- Saplings can easily be left at the apex of the A-shape, to grow into hedgerow trees.
- Growth is encouraged at the base of the hedge, where it is most needed.
