Influence of Transplanting Depth
on Norfolk Island Pine Growth and Quality

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University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-A Research Report, RH-92-3

R.T. Poole and C.A. Conover*

Popular journal articles discussing transplanting of foliage and woody ornamentals advise growers to place root balls at the same depth in the growing medium as the roots had been before transplanting (3, 5). This recommendation, however, is based on old information (4), and no recent research is available on the effects of placing root balls of woody ornamentals at depths different than where roots were prior to repotting. The following experiment was conducted to examine the effects of transplanting Araucaria heterophylla (Salisb.) Franco (Norfolk Island pine) with root balls placed in medium deeper than roots were when growing in their original containers.

Materials and Methods

This experiment was initiated on 12 February 1991 when good quality Norfolk Island pine plants, 15 to 20 cm (6 to 8 in) tall, in 10 cm (4 in) pots were obtained from local nurserymen. Plants were transplanted into 20 cm (8 in) containers using a medium composed of Florida sedge peat, pine bark and builders' sand, in a 6:3:1 combination by volume, amended with 3 kg/m³ (7 lbs/yd³) dolomite and 0.45 kg/m³ (1 lb/yd³) Micromax (a micronutrient blend manufactured by Grace/Sierra Co., Milpitas, CA 95305). Norfolk Island pines were placed in pots so that the top of the root mass was 1, 3, 5, 7 or 9 cm (0.4, 1.2, 2.0, 2.7 or 3.5 in) below medium surface, and 10 replicates were planted for each of the 5 planting depth treatments tested. Plants were grown in a shadehouse where maximum light intensity at plant level was 3500 ft-c and minimum and maximum air temperatures were 16C (60°F) and 35C (95°F), respectively. Plants were watered 2 to 3 times per week, as needed to maintain medium moisture levels needed for healthy growth. Osmocote 19-6-12 (Grace/Sierra Co., Milpitas, CA 95305) was surface applied to medium, 5 g/20 cm (8 in) pot, on 12 February, 4 June and 18 October 1991.

Plant height (cm) was measured 1 March, 17 June and 26 November 1991. Plants were graded using a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality plants on 14 November 1991. Research was concluded on 26 November 1991, after final height measurements were recorded.

Results and Discussion

Tallest plants, after about nine months of growth, were those with tops of root balls placed 5 or 7 cm (2.0 or 2.7 in) below growing medium surface (Table 1). Plants with root ball tops transplanted 5 or 7 cm (2.0 or 2.7 in) below medium surface also received higher plant grades compared to other plants grown in this test (Table 2). Pines with root systems transplanted 1 cm (0.4 in) and 9 cm (3.5 in) below medium surface were not as sturdy as plants with root systems transplanted at the other levels tested.

When transplanting root balls of Norfolk Island pines from 10 to 20 cm (4 to 8 in) pots in this experiment, plants grew better when root balls were placed 5 or 7 cm (2 to 2.7 in) deeper than they were originally located in the 10 cm (4 in) pots.

Additional Reading

1. Crockett, J.U. 1971. Evergreens. Time-Life Books, New York, NY.

2. Fullaway, E.T., T.K. Tagawa, E.Trujillo, C.J. Davis, A.A. LaPlant and E.Pung. 1972. Norfolk Island pine culture. Hawaii Univ. ext. circ 453, 16 pp.

3. Logsdon, B.B. 1973. Growing the Norfolk Island pine. U.S. Forest Service Tree Planters' Notes. 24(2):33-36.

4. Nicholls, R. 1975. Plants and pots pp 19-26. In: The Plant Doctor. Running Press, 38 South Nineteenth Street, Philadelphia, Pennsylvania 19103.

5. Pirone, P.P. 1978. Tree Maintenance, 5th Ed., p 44. Oxford Univ. Press, New York, NY.

6. Rice, L.W. and R.P. Rice, Jr. 1986. Indoor plant maintenance pp 315-339. In: Practical Horticulture. Prentice-Hall, Englewood Cliffs, NJ 07632.

Table 1. Height (cm) of Araucaria heterophylla transplanted at various depths on 12 February 1991, and height change, measured from 1 March until 26 November 1991.

^z Final plant height measured on 26 November - Initial plant height measured on 1 March = height change.

Table 2. Plant grade of Araucaria heterophylla transplanted at various depths on 12 February 1991. Plants graded on 14 November 1991.

^z Plants were graded on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality plants.

*Professor of Plant Physiology and Professor of Environmental Horticulture and Center Director (retired 7/96), respectively, Central Florida Research and Education Center - Apopka, 2807 Binion Road, Apopka, FL 32703-8504.