Propagation protocol for desert peach (Prunus andersonii [Rosaceae])

Seed Collection Information

Seeds are hand-collected at several sites in the local area where it is found in dense stands between mature big sagebrush and antelope bitterbrush. Fruits must be monitored often when near-ripe, because rodents will strip plants seemingly overnight once fully mature. Fruits are kept in woven polypropylene seed bags in a walk-in cooler at 1.7 °C (35 °F) prior to cleaning.

Fruits are mixed with water in buckets and allowed to open-ferment at room temperature for up to 5 d to soften flesh. Fruits are then processed with a Dybvig macerator (Dybvig Seed Cleaner, Bob Mills, Astoria, Oregon) using a wet process to separate flesh from seeds. The resulting seed and flesh mixture is put into a bucket, and debris and unfilled seeds are floated off with a slow stream of water. This method results in high purity seed, though some insect-damaged seeds will remain.

Seeds are air-dried on wire mesh racks for 10 to 14 d depending on temperature, then stored in woven polypropylene seed bags in a walk-in cooler at 1.7 °C (35 °F) and ambient humidity. Seeds can retain good viability for up to 6 y under these conditions. We store seeds for 5 mo from harvest and cleaning to pre-treatment in early winter.

Desert peach fruits showing split skins and seed removed.

Methods Used for Seed Pre-treatment

Freshly harvested seeds will readily germinate if kept moist. In fact, WSN employees used to take freshly harvested fruits, soak them in water until the flesh could be removed, then keep the cleaned seed submerged until the endocarp split, at which time they were planted. With that method, germination rates were approximately 60%. We have no extant records of the resulting plants, however, and this summer sowing technique has been discontinued in favor of spring sowing.

Stored desert peach seeds exhibit a non-deep, physiological dormancy and require cold, moist stratification. The hard endocarp is permeable to water. Unlike many other Prunus L. species, desert peach seeds do not require scarification or mechanical removal of the endocarp or a prolonged after-ripening for full embryo development prior to stratification.

We place seeds in mesh paint strainer bags for a 48 h running water rinse, then soak them in a 5% household bleach solution for 15 min before placing seeds into a naked (no media), cold, moist stratification. Hydrated seeds are placed in a shallow layer in plastic storage containers under refrigeration at 1.7 °C (35 °F) for approximately 8 wk. Seeds are tumbled weekly to prevent mold formation. After 6 wk, we check seeds weekly for germination. Nevada seed sources germinate as early as 55 d after cold, moist stratification and continue to germinate over a several week period. Our germination percentages can be as high as 88%.

We plant germinants, just as the endocarp splits and the radicle emerges, into 164 ml (10 in³) Ray Leach cell containers filled with a pre-moistened growing medium of 1:1:1:1 composted bark, peat, vermiculite, and perlite (v:v:v:v). Pumice or cinder can also be used as a medium component for this species, since it prefers rapid drainage and good aeration, particularly if transplanted to larger containers. Irrigation practices are adjusted to allow the medium to dry well between irrigations because plants are susceptible to overwatering during germination and growth. We have also found desert peach susceptible to Fusarium root rot and now add Root Shield Plus granules to all our media at 1.2 kg/m³ (2 lb/yd³).

Seedlings are germinated in a greenhouse at a 27 °C day/13 °C night (80 °F/55 °F) temperature cycle. During germination, seeds are kept evenly moist. Seedlings grow quickly and are usually well established with true leaves approximately 4 wk after sowing. We have occasionally seen mutations in seedlings, such as red-purple leaves or narrow, linear leaves, which could be developed into interesting cultivars.

During active growth, we fertilize seedlings with a custom formulation of 200-50-150 ppm NPK and micronutrients every other week. Seedlings are grown in the greenhouse to provide optimum temperatures and to manage irrigation.

Seedlings are hardened in midsummer by reducing irrigation and fertilization and by moving seedlings to the outdoor growing facility where more air circulation and full direct sunlight appear to be beneficial. During the hardening phase, seedlings are fertilized with a custom formulation of 50-50-70 ppm NPK and micronutrients every other week. Irrigation is applied only when medium is dry. Seedlings are hardened outdoors for 8 to 16 wk prior to winter storage or outplanting.

Seedlings not planted by November are overwintered at the nursery in the outdoor lath house or unheated greenhouse, depending on expected winter precipitation. Care must be given to ensure that root systems remain relatively dry during dormancy and overwinter storage. Typically, seedlings are ready for outplanting during September and October, or the following April. Desert peach is a beautiful, tough, native shrub that deserves more consideration in both restoration and xeric landscapes.