1 sand:1 sphagnum peatmoss substrates than in 6 pine bark : 1 sand or 4 pine bark : 1 sand : 1 sphagnum peatmoss potting substrates.

Fertilization requirements for container grown pawpaw seedlings have recently been determined (Pomper et al., 2002b, 2002c). Slow-release fertilizers can be used to efficiently meet most of the nutritional needs of container-grown nursery crops. Osmocote is a popular encapsulated, slow-release fertilizer that provides a relatively constant supply of nutrients for plant absorption over a fixed time frame. Because fertilizers such as Osmocote release nutrients slowly, they eliminate the need for labor-intensive liquid fertilization that may lead to excessive nutrient leaching and contamination of ground water (Nelson, 1998). Osmocote, alone or in combination with water-soluble fertilizer, was used to successfully produce pawpaw seedlings. Osmocote 14–14–14 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 in containerized production (Pomper et al., 2002c). It can also be used at the lower rate of 0.81 kg·m⁻³ when supplemented with weekly applications of 500 mg·L⁻¹ of Peters

20–20–20 plus micronutrients liquid-feed fertilizer. If pawpaw seedlings are grown for longer than 4 months with Osmocote 14–14–14 as the sole fertilizer source in the potting substrate Pro-Mix BX, it is possible that seedlings will display micronutrient deficiency symptoms (author, unpublished). Thus, if pawpaw seedlings are to be grown in containers with Pro-Mix BX, or similar peat based medium, for longer than four months, the plants should receive a one-time application of soluble trace element mix (S.T.E.M.; Scotts Co., Marysville, Ohio) at a rate of 0.6 g·L-1 (8 oz/100 gal) about 3 months after sowing. Pawpaw seedlings grown for longer than 4 months in the potting substrate Pro-Mix BX may also develop calcium deficiency symptoms. One or more applications of calcium nitrate at a rate of 500 mg·L-1 should also be provided to pawpaw seedlings at 3 months after sowing to avoid the development of calcium deficiency symptoms in plants.

Finneseth et al. (1998b) reported that early pawpaw seedling development can be divided into four distinct stages including radicle protrusion, hypocotyl emergence, epicotyl elongation, and seedcoat abscission. At the time of epicotyl elongation, which can be more than 50 d after sowing, the radicle and developing root system can comprise up to 81% of the seedling biomass. When Osmocote was incorporated in the potting substrate at a rate of 2.22 kg·m-3 as the sole fertilizer source, seedling emergence and growth were hastened compared to control plants (Pomper et al., 2002c). This was likely the result of the acceleration of the four stages of seedling development due to Osmocote being incorporated in the potting substrate. High rates of Osmocote 14–14–14 [17.7 kg·m-3 (29.83 lb/yard3)] incorporated into Pro-Mix BX potting substrate can delay seedling development when compared to non-fertilized control plants (Pomper et al., 2002c), possibly due to seedlings being sensitive to high soluble salt levels.

time of epicotyl elongation, which can be more than 50 d after sowing, the radicle and developing root system can comprise up to 81% of the seedling biomass. When Osmocote was incorporated in the potting substrate at a rate of 2.22 kg·m-3 as the sole fertilizer source, seedling emergence and growth were hastened compared to control plants (Pomper et al., 2002c). This was likely the result of the acceleration of the four stages of seedling development due to Osmocote being incorporated in the potting substrate. High rates of Osmocote 14–14–14 [17.7 kg·m-3 (29.83 lb/yard3)] incorporated into Pro-Mix BX potting substrate can delay seedling development when compared to non-fertilized control plants (Pomper et al., 2002c), possibly due to seedlings being sensitive to high soluble salt levels.

Pawpaw seedlings will grow well in a medium that has a relatively low pH. Mandujano and Fulbright (1998) reported that pawpaw seedlings in containers grew well and appeared very healthy in the pH range of 5.0 to 5.6, but at pH 5.7 to 6.0 they observed some leaf curling and tip burn. A pH of 5.6 was determined for Pro-Mix BX before sowing pawpaw seeds (Pomper 2002b).

Elevated root zone temperatures have been reported to significantly increase nutrient uptake and dry weight production in plants such as passionfruit (Passiflora edulis) (Menzel et al., 1994), flowering and stem length for hydroponically grown roses (Rosa ×bybrida) (Moss, 1984), and nitrogen accumulation by apple trees (Malus ×sylvestris var. domestica) (Toselli et al., 1999). Bottom heating (32 °C) of containers hastens pawpaw seedling emergence from Pro-Mix BX by 9 d compared to ambient root-zone conditions (24 °C) (Pomper et al., 2002a). Seedlings subjected to bottom heat show increased leaf number (30%), plant height (32%), whole plant leaf area (94%), shoot dry weight (104%), root dry weight (50%), lateral root dry weight (125%), and total plant dry weight (87%). Bottom-heated seedlings also have a lower root:shoot ratio (25%) than plants grown at ambient temperature. Bottom heating of container grown pawpaw seedlings could decrease both the time to produce a saleable plant and the cost of heating greenhouses. Bottom heating also pro-