Propagation from Seed
Several methods of propagating pawpaw from seed have been described. The simplest method is to plant the entire fruit. More commonly, seed are removed from the fruit and washed before planting or storing. It is generally agreed that the seed should not be allowed to dry out (but see Georgiadis, 1983). For storing small quantities, place seed in a polyethylene bag with damp, not soggy, sphagnum moss and seal the bag.
Freshly collected seed have dormant embryos and must be stratified before they will germinate. Storage at 35 to 45o F (2 to 7o C) for 60 to 100 days has been recommended (USDA, 1948; Thomson, 1974). Stratified seed may be planted directly. However, Nichols (1986) reported more rapid germination when seed are soaked in warm water for 24 hours prior to planting and soil temperatures are kept at 75 to 80o F (24 to 27o C).
Seed should be planted 3/4″ to 1″ (2 to 2.5 cm) deep. Germination of fall-planted seed (not stratified) frequently does not occur until July and may continue irregularly throughout the summer. Seedlings are sensitive to strong sunlight and should be protected by light shade during the first year.
Two to three years from seed are usually required to obtain plants large enough to graft. Zimmerman (1941) stated that pawpaws graft very readily on any native [Asimina] stock. Chip-budding is a method that has been reported to be successful (Davis, 1983a). The use of Annona cherimola as a stock is successful the first year but graft incompatibilities become apparent the second, according to Thomson (1974).
Hardwood and root cuttings generally have not been successful. However, Hickman (1985) described a successful method of rooting softwood cuttings under intermittent mist. Cuttings 6″ to 8″ (15 to 20 cm) long with 3 leaves were taken in August. Leaves were cut in half. Cuttings were dipped in Rootone #10 (no longer available) and placed several inches deep into a medium consisting of 1 part coarse sand to 1 part peat moss. Bottom heat (80o F, 27oC) and supplemental light (14 hours) were supplied. Percentage of cuttings forming roots was low (Hickman, personal communication).
The author is unaware of any published reports on the propagation of pawpaw by tissue culture. While at Cornell University, the author successfully regenerated shoots from leaf tissue using a slight modification of a published medium. Shoots from these explants callused but failed to produce roots. The author feels that root regeneration would have been induced by transferring the explants to another medium and hopes to duplicate this work, as well as induce root formation, in subsequent experiments. Details of the procedure will be made available at that time.
Pawpaw has a reputation of being difficult to transplant. Plants should be transplanted at 12″ to 18″ (30.5 to 46 cm) tall while dormant. The addition of approximately 25% vermiculite by volume into the hole at planting is a commonly recommended practice. One nursery (Mellinger’s Inc., North Lima, OH) suggests dipping the roots into gibberellic acid before planting. Another practice thought to improve transplanting success is the addition of soil from the original hole into the new hole. Pawpaw is believed to have a symbiotic association with mycorrhizae. Those advocating this practice argue that soil from the original hole should contain this fungus and aid in its establishment at the new site, thus improving pawpaw transplanting success. Trimming back the top is often recommended when transplanting. A 12″ (30.5 cm) seedling should be pruned back to about 8″ (20 cm) when transplanting.