Container Production of Pawpaw Seedlings

Abstract

Pawpaw (Asimina triloba) is a native North American tree that has potential as a new fruit crop or for use in landscapes, but until recently, little information has been available to nurseries on containerized production of this species. Pawpaw seedlings develop a strong taproot with a fragile root system, which can be easily damaged upon digging; therefore, most nurseries propagate trees in containers. Pawpaw seed requires stratification for optimal germination and seed is sensitive to desiccation. The seed also cannot tolerate freezing temperatures [<-15 °C (5.0 °F)]. A well-aerated potting substrate with a high sphagnum peat moss component (>75% by volume), cation exchange capacity, and water holding capacity can be used effectively in container production. Tall containers should be used to accommodate the developing taproot of seedlings. The slow-release fertilizer Osmocote 14-14-14 (14N-6.1P-11.6K) incorporated into Pro-Mix BX potting substrate can be used effectively as the sole fertilizer source at a treatment rate of 2.22 kg·m-3 (3.742 lb/yard3) in containerized pawpaw production. It can also be used at a lower rate of 0.81 kg·m-3 (1.365 lb/yard3) when supplemented with weekly applications of 500 mg·L-1 (ppm) of Peters 20-20-20 (20N-8.78P-16.6K) liquid-feed fertilizer. Bottom heating [32 °C (89.6 °F)] of container-grown pawpaw seedlings results in greater lateral and total root dry weight than in seedlings grown at ambient temperature [24 °C (75.2 °F)], which could increase the rate of establishment of seedlings in the field. Bottom heating of container-grown pawpaw seedlings could decrease both the time to produce a saleable plant and the cost of heating greenhouses. Growth of containerized pawpaw seedlings is enhanced by low to moderate shading with polypropylene shade fabric (28% or 51%) outdoors and low shading (33%) in the greenhouse, in a manner typical of that reported for other shade-preferring plants. Low to moderate shading of pawpaw seedlings grown outdoors greatly increases leaf number, total leaf area, and total plant dry weight compared to nonshaded seedlings, suggesting that commercial nurseries can improve production of containerized pawpaw seedlings using a shading regime outdoors.