Robert H. Beede, UCCE Farm Advisor, Kings Co.
Typical Types of Pruning Cuts
- Heading cuts shorten a limb by cutting back to a lateral branch. They are used to stiffen limbs push the canopy upward.
- Thinning cuts remove a branch at its point of origin. They are used to reduce density within the canopy, and thus, improve light penetration. These cuts are also used to remove branches extending beyond the size of the catch frame of the harvester.
- Tipping cuts are used to reduce length of shoots (whips) at the top of the canopy and induce lateral branch development. It is important to retain 1 - 2 vegetative buds above the flower buds, to avoid shoot dieback to the next lateral after fruiting.
Rootstock seeds are germinated in commercial nurseries and the seedling are maintained in their greenhouses and moved outside. Growers obtain these from the commercial producers to transplant to the field. Pots may be either fibrous, which will be orchard-planted directly into the soil thus avoiding transplant shock, or plastic, which reduce water evaporation and provide more protection during handling.
The First Year
- Planting: unbudded rootstocks, approx. 1 year old, are planted into the orchard from January to early May. Plants should be immediately staked and irrigated. Subsequently, a program of regular fertilization and irrigation is to maintain vigorous growth.
- Staking: Note that stakes are manually placed next to the root ball, not into it. Use 2 x 2 in. stakes, 6 ft. long, placed 12 - 18 in. into the soil. Locate the stake so the tree blows into the stake with the prevailing wind.
- Field Budding: pistachio scions are typically budded to rootstock in early summer, but may continue as long as the rootstock bark slips. T-budding it the most common. Bud the tree at a height of 24 -28 inches. At harvest, the shaker attaches at 19 - 22 in., and the bud should be placed above this zone.
- Caution: Do not attempt to head the scion shoot to grow primary scaffolds (the first branches) in the first growing season. It is of no advantage, because the short laterals that begin to grow are not long enough to be left as scaffolds during dormant pruning, so they are usually removed, and there is no gain.
- First Heading Cut: Scion shoots are headed at 42 in. during the first dormant season. This dormant cut will stimulate more lateral branching than an in-season cut. The only circumstance in which the first heading cut is in-season is when the tree does not reach 42 in. in the first season. In this case, the first heading cut must be made during the second growing season. A two-scaffold tree may result, typically not as strong as a three-scaffold tree.
The Second Year
Trees will typically have several growing laterals destined to become primary scaffolds – structural rather than fruiting - branches. These are tied high, vase-like, to keep them upright, and pinched in the growing season, to 14 in. Let the secondaries grow, to maximize canopy area and increase girth in developing scaffolds. Development of secondary and tertiary branching in the same season is not advised - heading the secondaries would leave the tree spindly and vulnerable to injury.
- Branching of these primaries can be improved by clipping the leaf blade from its petiole at the second node from the terminal.
- Lateral growth on the rootstock and scion are pinched, and growth close enough to the ground to be herbicide-affected may be removed.
Second Dormant Season Pruning
- Secondary branches are thinned to 2 - 3 branches per primary; limbs selected to retain should not be directly opposite each other.
- Secondaries are headed to 11 - 13 in. and tied in an upright vase shape.
Years 3 - 5
Trees now have primaries, branching to secondaries, branching to tertiaries. Let these grow.
Third Dormant Season Pruning
- For each secondary scaffold, tertiary branching is thinned. Select the retained branches for strength and position. Follow the method of Ratio Pruning, when thinning branches, 2:1 for scaffolds. That is, retain 2 secondaries for each primary, and 2 tertiaries for each secondary.
- Mark your pruning shears at 16 and 22 inches, with tape, to measure branch lengths as you prune. Measure the distance from the origin of a secondary out along the tertiary. If the branches are vigorous, head the tertiary where this total distance is 22 in.; if branches are weak, head the tertiary where this total distance is 16 in.
- Tie up the tertiaries, high on the branch, including cross-typing within the canopy. Opening of center of the tree is not advised as this reduces early bearing potential.
- Some fruitwood branches may develop down the scaffolds. Another aspect of Ratio Pruning is to keep one fruitwood branch to each structural branch.
Years 6 – 8
Once the basic shape of the tree is established, minimize the number of pruning cuts; this enhances and distributes spur development, thus promoting fruitfulness.
Dormant Season Pruning
- Pruning of trees just coming into production mainly consists of small heading cuts to develop canopy and strengthen fruiting wood. Heading cuts on 1-year old whips develop canopy area. Vigorous whips are cut to 18 -22 in. and weak whips are cut to 16 in.
- Use heading cuts to tip the fruitwood, to strengthen it. Leave vegetative buds above the fruiting buds or these fruiting whips will not branch and will die after the first season.
- Prune branches that will interfere with harvesting equipment.
- The ‘knuckle-cut’ can be good for nut production. A knuckle is a ‘whorl of buds’, where internodes are compressed. A cut just above the knuckle will produce many branches with flower buds. These are particularly useful on flat limbs, but are not good for building structure.
- The tree is divided into zones, based on the primary scaffolds. Some thinning cuts may be used to keep wood within their zones.
A main objective of pruning is to confine trees to their allotted space and promote light penetration for viable nut production throughout the tree. Due to apical dominance, the most vigorous shoots develop from buds closest to the terminals, adding growth to the upper canopy and lateral margins of the canopy. Main bearing limbs also tend to become less upright with each year. This situation limits light penetration to lower fruit wood, and the result is a crop that is high in the canopy and further from the center of the tree, thus difficult to harvest. Mature tree pruning begins on the ground with hand shears. For the upper canopy, switch to pole pruners.
Dormant Season Pruning
- Thinning cuts to remove broken, and closely overlapping branches. When removing overlapping branches, preserve the higher branch.
- Thinning cuts to remove branches to push bearing branches upright; remaining branches should point up, not out. These cuts are typically on the periphery.
- Heading cuts of 1 yr-old whips – there are fewer in older trees.
- Tip the fruitwood.
- Saw Cuts: Using a hand saw, remove lower limbs which no longer produce fruiting wood. Start with an undercut, about an inch from the scaffold, then cut the branch from the top. Saw just beyond the ‘bark inclusion layer’, which generates callus tissue to heal the wound.
2012 PISTACHIO DAY PRESENTATION (PDF of PowerPoint)
Research Update on Planting Pistachios in Saline Soils
Blake Sanden, UCCE Irrigation and Soils Farm Advisor, Kern County
Source: Pistachio Production Manual, 5th Edition (2008)