HEDGEROW VS. STANDARD HIGH-DENSITY MANAGEMENT SYSTEMS FOR WALNUTS

Walnut orchards in California are commonly planted at 120 trees/ha with trees equally spaced in the row and between rows (9 x 9 m). The trees are trained to a modified central leader and attain full canopy and production within ten to twelve years. These orchards tend to become crowded, resulting in an elevated bearing area, and reduced nut size and quality as the trees become larger. Tree thinning is seldom practiced. Growers would prefer to maintain tree size and canopy light exposure by regular pruning, but many of them question the value of pruning walnut trees because of the amount of labor and equipment required. Biennial pruning has been shown to be one method to reduce labor requirements and yet control tree size, sustain crop production, and improve nut quality.

An attractive alternative to hand pruning to maintain productivity of closely planted orchards is mechanized tree hedging. Experimental results have shown that once walnut orchards become crowded, hedging to allow light between trees does not effectively alleviate the condition. Mechanical hedging, however, may be valuable in maintaining tree size and production of precocious lateral-bearing varieties where trees have not yet become crowded.

Hedgerow planting of lateral-bearing walnut cultivars is another method to increase early returns on investments and develop a more efficient high-density management system for walnuts. The trees are trained to produce a continual wall of foliage and nut-producing shoots in response to mechanical side hedging. The wall not the single tree becomes the management unit in the orchard. Higher early yields and the use of mechanized hedging machines for pruning are the major advantages. High initial cost is the primary disadvantage due to the increased number of trees/ha.