Stone Fruit Propagation by Cuttings
Direct stick cutting propagation is common for several clonally propagated rootstock varieties that do not produce “true-to-type” seed (Hartmann, Kester, Davies, & Geneve, 2002). Cuttings are typically taken from the previous season’s lignified growth, although two year old growth can be used for plum rootstock varieties in the late fall or winter. Plum is the easiest stone fruit to root by cutting.
Hardwood cuttings should be collected from healthy exterior shoots growing in full sunlight, with normally spaced internodes. Cuttings should not be collected from overly vigorous or weak shoots. Basal or central stem portions of last season’s growth have the best rooting ability. Leaves attached to cutting wood should be removed prior to storing or sticking and the stem terminus should be removed prior to rooting. Although rooting percentage is increased when cuttings are collected from October to January (Loreti & Morini, 2008), the ideal time frame for collecting cuttings varies among varieties.
Hardwood cuttings 10 to 12 inches in length are needed for rootstocks to enable scion bud insertion (Loreti & Morini, 2008). Rootstock cuttings should be ¼ inch to 1 inch in diameter, depending on the method of budding used (Hartmann, Kester, Davies, & Geneve, 2002). The bottom cut should be made directly below a node while the apical cut should be made ½ inch to 1 inch above the uppermost node. Disbudding, removal of lower axillary buds prior to sticking, will reduce suckering. However, do not remove all buds on the cutting because new leaf growth in the spring is needed to provide photosynthates to the growing bud and new root system. If prepared cuttings will not be used immediately after collection they should be bundled, make basal and apical cuts with a band saw, and dip tips in wax to prevent drying and indicate terminal orientation. Cuttings should then be stored in moist (not soaking) peat moss, newspaper or sawdust, placed in polyethylene bags, and refrigerated at 32-40°F (Westwood, 1993, p. 120; Hartmann, Kester, Davies, & Geneve, 2011, p. 350).
Check cuttings frequently to make sure buds remain dormant. In some varieties that are difficult to root it may be necessary to use rooting hormones, callus formation, or root initiation prior to cold storage. Soak basal cuts in IBA at 10-25ppm for 12-24 hours, or quick dipped in1000-5000ppm IBA for 5 seconds in IBA (Westwood, 1993, p. 117; Loreti & Morini, 2008, p. 226). Place the basal portion of the bundled cuttings in 3 inches of moist peat above 8 inches of sand above heating mats or circulating hot-water tubing. Maintain bottom heat at 18 to 21°C and expose the top portion to cold air to ensure bud dormancy (Hartmann, Kester, Davies, & Geneve, 2011, p. 350). Cuttings can also be spaced closely together, if bundling is not desired, in liners or beds with bottom heat similar to those used for bundle cutting wood. Field transplantation must occur before bud dormancy is broken.
Direct Spring Planting
Orchard soil should be prepared and fumigated prior to planting. Rooted liners should be planted at high density spacing in prepared beds in late February to early March. Budding occurs between late May and early June.
Direct Fall (Summer) Planting
California’s mild winters permit direct planting in the fall. This form of propagation requires less labor and space because prepared rootstock cuttings are rooted directly in the field, not in liners or heated propagation beds. Cuttings should be planted in nursery rows between November and December and allowed to root over winter (LaRue, 1989). Peach, and peach x almond hybrid, rootstocks should be treated with IBA prior to sticking. Once buds from rootstock cuttings start to break dormancy prune them to allow only one bud to grow. June budding on rooted cuttings should be done in late May to early June.
Several Prunus species and cultivars are listed in the UC Davis Plant Sciences Rooting Database at http://rooting.ucdavis.edu/pchome.htm (Burger, 2009) with a brief overview of cutting type, rooting method, and percent success. Although propagation with hardwood cuttings is still used, tissue culture is becoming more popular.