Your Walnut Tree
Selecting a good planting site
All walnuts species grow best on fertile soils that are deep (90cm or 3ft minimum) and well drained. The ideal pH is near neutral (5.5-7.5). Avoid frost pockets in valley bottoms and any area prone to water-logging. They will not grow well in compacted soils, or those with a gravel layer or iron pan close to the surface. Exposed sites and those with steep slopes should be avoided. Gentle slopes near the valley bottom are optimal because cold air is drained away from the trees and water availability is high.
Hybrid walnuts are more tolerant of drier conditions and poorer soils than either common or black walnuts. On marginal sites hybrid walnuts show very strong growth over the other walnuts but on optimal sites the differences are minimal.
Preparing the site and planting
Good site preparation is essential and ideally should involve the break-up of any compacted solids, removal of weeds and, if necessary, improvement of drainage. It is always a good idea to mix a mulch or compost to the soil when planting. Walnuts are best ‘pit’ planted. Make sure the pit is several inches wider and deeper than the root-ball. Place the tree centrally and ensure the roots are evenly distributed. Water in well and continue to water as necessary over the first growing season.
Spacing and growth
Trees grown for fruit production need a lot of space for crown development. Trees are usually spaced at a minimum of 7m x 7m (204 trees per hectare) and grown as a monoculture. For timber production, trees are normally spaced at a minimum of 5m x 5m (400 trees per hectare) and inter-planted with other trees and shrubs to create a habitat that will encourage the trees’ straight growth required for timber production.
All walnuts will grow into large trees given the right conditions and space. Trees can grow up to 25 metres (80 feet) or more, and can have very wide, spreading crowns (canopies). Growth rates vary considerably depending on species and site conditions, the most rapidly growing are the hybrids that can increase in growth by over a centimetre each year in diameter and by several feet in height.
Feeding and pruning
Walnuts like to be well fed and it is a good idea to provide them with a good quality mulch or nitrogen rich fertiliser early in the spring. Do not fertilise in late summer as this can encourage late vegetative growth that can be susceptible to frost damage. Pruning should be carried out only in mid winter or mid summer. Start by removing dead, damaged or badly forking branches. Do not remove more than 20 percent of the crown at any one time.