Effects of N and K Ratios on Growth of Holly Fern Cyrtomium falcatum

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C.A. Conover, Ph.D.and K. Steinkamp

Central Florida Research and Education Center
CFREC-Apopka 2807 Binion Road,
Apopka FL 32703-8504

Holly fern, (Cyrtomium falcatum), are grown by the foliage plant industry in central Florida for use in landscape plantings, interiorscape beds and as potted specimen plants. Holly fern were not included in the extensive research which produced our fertilizer recommendations for production of acclimatized foliage plants. We recommend a 3:1:2 N-P-K fertilization ratio for production of most acclimatized foliage plants when soilless media are used (Conover and Poole, 1990). However, there are some exceptions to this general rule. In two different experiments, maidenhead fern (Adiantum raddianum K. Presl) and bird's-nest fern (Asplenium nidus L.) grew better when plants received more K compared to N (Poole and Conover, 1982; Poole and Conover, 1978). The following experiment was conducted to determine the optimum N:K ratio, N rate and K rate for production of quality holly fern.

On November 8, 1994, small holly fern plants growing in 72-cell pack trays were transplanted into 6-inch (15-cm) standard tub pots using Fafard #4 growing medium (Fafard of Florida, Inc., 3723 Hogshead Road, Apopka, FL 32703) amended with 1 lb/yd³ (.593 kg/m³) Micromax (The Scotts Company, 6656 Grantway, Allentown, PA 18106). Plants were maintained in a greenhouse where maximum light intensity was about 1500 ft-c (285 µmol m•^-2 •s^-1) and air temperatures ranged from 65 to 90°F (18 to 32°C).

This was a 4 nitrogen (N) rate x 4 potassium (K) rate factorial experiment, with six replications per treatment. On November 15, 1994, fertilizer treatments began. Plants were fertilized once per week with 100 ml liquid feed made from concentrated stock solutions. Nitrogen rates used were 600, 1200, 1800 or 2400 lbs/A/yr (1.39, 2.46, 4.17 or 5.56 g/15-cm pot/yr) and K rates tested were 600, 1200, 1800 or 2400 lbs/A/yr (1.39, 2.46, 4.17 or 5.56 g/15-cm pot/yr) All fertilizer formulations tested contained phosphorus at 400 lb/A/yr (0.82 g/ 15-cm pot/yr).

Initial plant height and width (cm) were determined on November 16, 1994. Plant height and width were measured again on February 15, 1995, after three months of growth, and for the final time on May 19, 1995, after six months growth. For quantitative purposes, plant size was defined using the formula; height + (width + width) ÷ 2) ÷ 2 = plant size. Plant growth after three months was defined using the formula; plant size on February 15 - initial plant size = plant growth. Plant growth after six months was defined using the formula; Size on May 19 initial size = plant growth.

Holly fern were graded based on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality, on May 16, 1995. Electrical conductivity and pH of leachate collected from container growing medium were determined after three and six months of growth. Leachate collection dates were February 17 and May 18, 1995. The experiment was terminated on May 19, 1995.

Results

Interaction of N and K fertilizer treatments did not significantly affect plant quality, growth, or pH and electrical conductivity levels in growing medium leachate. Both growth and quality improved greatly when N rate was increased from 1.39 to 2.46 g (Table 1). Further increases in N rate produced slightly smaller plants with little improvement in plant quality. Holly fern quality as reflected by plant grade was not influenced by K fertilization, but plants getting the high K rate were slightly smaller compared to plants receiving less K.

As N rate increased pH of growing medium leachate decreased (Table 2). After three months growth electrical conductivity of growing medium leachate was increasing as N rate increased, but after six months growth, EC was very variable and not significantly affected by N fertilization. Potassium did not significantly affect pH of growing medium leachate but EC of leachate increased as K rate increased, for leachate collected at both sampling times.

Conclusions

Since more that 1200 lb/A/yr N, did not improve plant growth and quality and high K rate slightly slowed plant growth, we can recommend use of a standard 3:1:2 ratio fertilizer for holly fern. For production of good quality plants and to reduce excess fertilizer ion accumulation in growing medium, N fertilization rate should not exceed 1200 lb/A/yr.

1. ^ZPlant size was defined using the formula: (height + width + width) 2) 2). Initial size, measured on November 16, 1994, average 10.6 cm. Size after three months of plant growth was measured on February 15, 1995 and size after six months of plant growth was measured on May 19, 1995. Plant growth on February 15 was determined using formula: Plant size after three months growth - initial plant size = growth. Plant growth on May 19, 1995 was determined using the formula: plant size after six months growth - initial size = growth.
   ^YPlants were graded based on a scale of 1 = dead, 2 = poor quality, usable, 3 = fair quality, salable, 4 = good quality, and 5 = excellent quality, on May 16, 1995.
   ^Xns, *, **; Nonsignificant at P = 0.05 or significant at P = 0.01, respectively.

1. ^ZElectrical conductivity and pH levels of growing medium leachate collected from containers of holly fern were determined from leachate collected on February 17, 1995, after three months growth, and on May 18, 1995, after six months plant growth.
   ^Yns, **; Nonsignificant or significant at P = 0.01, respectively.

References

1. C.A. Conover and R.T. Poole. 1990. Light and fertilizer recommendations for production of acclimatized potted foliage plants. Nursery Digest 24(10):34-36, 58-59.
2. R.T. Poole and C.A. Conover. 1982. Fertilization of Bird's-nest fern, Asplenium nidus L. Proc. of the Trop. Reg. Amer. Soc. Hort. Sci. 25:81-87.
3. R.T. Poole and C.A. Conover. 1978. Fertilization of maidenhair fern, Adiantum raddianum K. Presl. HortScience 13(2):176-177.