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THE GJERDE METHOD FOR TRAINING RASPBERRIES. EFFECTS OF INCREASING CANE NUMBER AND CANE HEIGHT
The method uses a 80–100 cm crossarm trellis with two adjustable wires, on to which the fruiting canes are trained each spring.
The two rows of canes are kept 30 cm apart until flowering, whereafter they are moved apart 80–90 cm.
This allows the fruit to ripen on the outside of the rows, whilst the new canes grow up within the V-formed hedge.
This system gives higher yield than the previously used 30 cm crossarm trellis.
Ten fruiting canes per metre tipped at a height of 1.80 m, has given the highest yield in trials.
However, most pickers find a tipping height of 1.60 m more convenient, and fewer than ten canes per metre are usually retained in commercial plantings.
In larger fields a row spacing of 3.25 – 3.50 m is now common.
The Gjerde method is based on a crossarm trellis with two adjustable wires, on which canes are whipped by means of plastic garden tape, or, more recently, "Gjeldstad’s patent plant holder". A crossarm length of 80–100 cm is used instead of the more usual 30 cm.
The wires are no longer stapled to the crossarm, but attached loosely on nails or notches, so that the distance between them can easily be adjusted from 30 cm to 80–90 cm (Fig. 1).
The canes are held 30 cm apart from spring until flowering.
This encourages most of the laterals to grow towards the outsides of the hedge.
Once flowering is well advanced, the wires are moved 80–90 cm apart, and any new canes that remain on the outside are bent inwards.
The benefit of this system is to separate fruiting canes from new canes, hence facilitating picking.
In a trial using cv. ‘Veten’ with 34 000 fruiting canes per hectare (row width 2.5 m, 8.5 canes per metre) and a tipping height of 1.70 m, this method gave 20.95 tons per hectare, outyielding the older method of training by 1.25 tons, as an average over two years.
Furthermore, fruit ripening was brought forward by the separation of the old and new canes.
The Gjerde method also led to higher picking rates, despite a reduction in fruit size with this method in the second year.
Average picking rates were 5.73 and 5.49 kg per hour, for the new and old training methods respectively (16 pickings in first year, 14 in second year).
In the third year of this trial, the number of fruiting canes retained in spring was raised to 10 per metre, and the tipping height raised to 1.80 m.
The crossarm was lengthened to 90 cm and its height