How To Train Young Walnut Trees

How To Train Young Walnut Trees

Training young walnut trees occurs in the first 1 to 6 years in the life of an orchard. Traditionally it has been done using a modified central leader with a minimum pruning style; the basics are similar for standard spaced or hedgerow orchards. We believed for decades that if lateral bearing walnuts were not pruned, their growth would stall out from early cropping. Research conducted since 2004 investigating pruning versus non-pruning on young walnut tree growth and productivity however, has challenged that paradigm.

Results from trials on Howard and Chandler have shown that young walnuts do not need to be pruned in order to keep them growing or to produce adequate yields. In general, unpruned trees have produced higher early yields and equivalent yields in year 5 and beyond compared to minimally pruned trees.

With more knowledge comes more complexity. Growers now need to decide when trees are a year old (first dormant pruning), whether to stick with the modified central leader and train using minimum pruning or to not prune, which saves on labor and brush disposal. Growers interested in trying the unpruned method may want to start small and compare their results to the minimal pruning method to make sure it fits their management system.

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If you start with minimum pruning, we recommend that you continue with the same method until the trees are mature. Changing midstream from pruning to no pruning may lead to limb breakage, especially if trees were heavily pruned, and this leads to lower early yields and is not recommended.

An unpruned tree on left (note short shoot growth on primary branches) and a minimum pruned tree on right (note secondary scaffold extension growth  from heading cuts) at the end of the third growing season.  (Photo Credit: Bruce Lampinen)

An unpruned tree on left (note short shoot growth on primary branches) and a minimum pruned tree on right (note secondary scaffold extension growth from heading cuts) at the end of the third growing season.
(Photo Credit: Bruce Lampinen)

Below are the main steps comparing training walnuts for years 1 to 3 using the modified central leader with the minimum pruning method to the unpruned training method. The assumption is you are using a standard-spaced orchard and differences for hedgerow systems are noted. Always remove suckers from the rootstock.

Modified Central Leader With Minimum Pruning Method
Pruning 1-year-old walnut trees:
• The shoot (leader) selected to be the trunk should have reached a height of at least 7 to 8 feet. Ten feet or more of growth is better (7 to 8 feet is sufficient for hedgerow orchards).
• Heading the leader at 8 feet will give more area for the scaffolds. The leader should not be headed any less than 6½ feet since the first primary scaffold should be at least 5½ to 6 feet above the ground so as not to interfere with equipment operation (for orchards, hedgerow head at 6 feet, and the first primary should be about 4 feet above ground). Make the heading cut into mature round wood.
• Any lateral shoots on the leader should be removed. One or two nonvigorous shoots arising below the leader can be stubbed to two to three buds to provide shade on the southwest side and aid caliper growth. They will be removed in the next dormant season.
• Primary buds above 5 feet from the ground that are necked should be rubbed off to the side so as not to damage the secondary bud. If left, necked buds form weak limb attachments that are subject to breakage. The secondary bud which is forced to grow will form a wide angle and develop a strong crotch.
• If the shoot selected to be the trunk has not reached sufficient height, cut it 3 to 6 buds above the point of origin and remove competing shoots. A stronger shoot can then be trained as the trunk over the summer.

Pruning 2-year-old standard-spaced walnut trees:
• The goal is to select four to six primary scaffolds arising from the trunk in years two and three. Select the central leader which is typically the topmost branch.
• As with the 1-year-old trees, the height of first primary scaffold should be 5.5 to 6 feet above ground.
• Select other primary scaffolds to form a spiral pattern around the trunk. Space them at least 8 inches apart. Primary scaffolds should never originate directly opposite each other to prevent the leader from getting ‘choked out’.
• Selected scaffolds should be angled about 45 degrees from the vertical. Limbs with narrower angles or bark inclusions are usually poorly attached and cannot support heavy crops. Branches with wider angles of attachment may fail to grow vigorously.
• For most lateral-bearing varieties, head all primary scaffolds to ¼ to ⅓ of current growth, depending on vigor and variety. Tulare are very vigorous and need only tipping or no heading of the scaffolds. The leader should be left the longest.
• Remove forked branches on chosen scaffolds to a single branch. Leave remaining unselected branches and small caliper wood unheaded to create early fruiting wood.

Pruning 2-year-old hedgerow walnut trees:
• Select a central leader and two to four side limbs oriented in opposite directions in the tree row.
• Remove branches below three feet that will interfere with shaking and flat limbs that grow out into the middles.
• Depending on variety and vigor, selected framework limbs should be headed or tipped (see above) and cut to an outside bud facing into the tree row. Other branches can be left unheaded to fruit early.

Pruning 3-year-old standard-spaced or hedgerow walnut trees (Photo- right tree):
• Choose the strongest, tallest scaffold for the leader and head ¼ to ⅓ of the current growth. Strong secondary scaffolds in a vertical position can be tipped or left unheaded. Head or tip one strong secondary scaffold on the canopy in each cardinal direction ¼ to ⅓ of the current growth.
• Forked branches can be left but twisted, rubbing or overlapping branches should be removed.

Unpruned Training Method
1-year-old walnut trees:
• The shoot (leader) selected to be the trunk should have reached a height of at least 7 to 8 feet. Ten feet or more of growth is better (7 to 8 feet is sufficient for hedgerow orchards).
• Leave the leader selected as the trunk unheaded.
• Remove lower limbs below 4 to 5 feet (3 to 4 feet for hedgerows).
• Place a long stake extension on existing stakes to support the unpruned leader.

2- and 3-year-old walnut trees:
• No pruning or heading unless lower branches need to be removed for reasons of safety or ease of maintenance and harvest.
• Note that unpruned walnuts tend to put on extension growth in alternate years. Individual shoots follow a pattern of extension growth, followed by side branching occurring on shoot with 5 to 8 inches growth on the end (Photo – left tree), followed by another year of extension growth.
• Unpruned trees tend to grow as a central leader with the primary branches naturally well-spaced along the trunk and at wide angles.