BENEFITS OF PROGRESSIVELY INCREASING CONTAINER SIZE DURING NURSERY PRODUCTION DEPEND ON FERTILIZER REGIME AND SPECIES

Rooted photinia (Photinia x fraseri) cuttings and bare-root slash pine (Pinus elliottii Engelm.) seedlings were transplanted initially into 0.9-, 2.9-, and 10.2-liter containers. A subset of these plants was transplanted from 0.9- and 2.9- liter containers into the next larger container size in the series (upcanning) until representative plants of each initial container size were growing in 10.2 liter containers. The photinia experiment was conducted with two fertilizer regimes [soluble vs. controlled-release (CR) fertilizer] superimposed. When CR fertilizer was used, upcanning from 2.9- to 10.2-litre containers produced the largest photinia. However, for pine, there was no advantage due to upcanning. When soluble fertilizer was used, photinia initially transplanted into 0.9-liter containers and upcanned to 2.9- and then to 10.2-liter containers had superior growth compared to those of other fertilizer x container combinations. Upcanning generally maintained or increased plant growth rate, while growth rates of plants kept in the same container generally declined the second season. Improved efficiency of the root system in nutrient absorption of upcanned plants is proposed as the mechanism for this response.