The response to fertilization of newly planted woody plants and established specimens appears to vary greatly depending on time because of transplanting, species, soil type, climate, method of application, and type of fertilizer (Struve, 2002). Fertilizer recommendations for deciduous trees or shrubs growing in loam or clay soils in temperate climates would not be expected to be appropriate for evergreen species growing in sand soils in subtropical climates such as that of peninsular Florida. Relatively little research has been published on fertilizer requirements of shrubs in sand soils of Florida and much of that has used chinese hibiscus (Hibiscus rosa-sinensis), a species that may be atypical for tropical and subtropical shrubs because of its high nitrogen requirements (Broschat and Moore, 2010; Gilman, 1987, 1988).
Fertilizer requirements for woody plants during the first year after transplanting may be different from that of established plants. Shober et al. (2013) found no response to N fertilization in indian hawthorne (Rhaphiolepis indica) or sweet viburnum (Viburnum odoratissisum) after 100 weeks or at any time before that, but did observe an increase in rose (Rosa ‘Knock Out’) size with increasing N fertilization rate. Gilman and Yeager (1990) did not notice differences in growth between fertilized and unfertilized laurel oak (Quercus laurifolia) during the short 17-month duration of their study, but did find an increase in growth with increasing N fertilization rates in japanese ligustrum (Ligustrum japonicum). Gilman et al. (2000) also did not observe differences among treatments in the growth of southern magnolia (Magnolia grandiflora) during the first year after planting, but treatment differences were noted after the third and fourth year. On the other hand, fertilized live oak (Quercus virginiana) was larger than unfertilized trees during the first year, a trend that continued for 4 years (Gilman et al., 2000).
Most fertilizer studies on woody plants have concentrated on N requirements, yet in Florida landscapes, N deficiency symptoms are seldom observed. Magnesium (Mg) deficiency is fairly common on such trees (Dickey, 1977), but it is not known if routine application of Mg-containing fertilizers would result in superior growth or visual quality. Gilman et al. (2000) reported no response to applied phosphorus (P) or K in live oak, but this species rarely exhibits deficiencies of any nutrient element in the landscape. Broschat et al. (2008) found no response to fertilization in pentas (Pentas lanceolata) or dwarf allamanda (Allamanda cathartica ‘Hendersoni’), but nandina (Nandina domestica) grew larger with N-containing fertilizers than unfertilized controls. Fertilizer type (turf formulation that contained mostly water soluble N, P, and K or a palm formulation that contained controlled release N, K, and Mg plus water soluble micronutrients) made no difference.
The objective of this study was to determine how three woody shrubs commonly grown in south Florida respond to different types of fertilizer; a typical turf fertilizer that contains no Mg or water soluble micronutrients and two palm fertilizers that contain large amounts of K and Mg plus soluble micronutrients, and to determine if fertilizer rate was important, both during and after establishment.
Broschat, T.K. 2015 Fertilization of landscape palms to reduce nitrogen and phosphorus impacts on the environment HortScience 50 469 473
Broschat, T.K. & Moore, K.A. 2010 Effects of fertilization on the growth and quality of container-grown areca palm and chinese hibiscus during establishment in the landscape HortTechnology 20 389 394
Broschat, T.K., Sandrock, D.R., Elliott, M.L. & Gilman, E.F. 2008 Effects of fertilizer type on quality and nutrient content of established landscape plants in Florida HortTechnology 18 278 285
Dickey, R.D. 1977 Nutritional deficiencies of woody ornamental plants used in Florida landscapes. Univ. Florida Agr. Expt. Sta. Bul. 791
Gilman, E.F. & Yeager, T.H. 1990 Fertilizer type and nitrogen rate affects field-grown laurel oak and Japanese ligustrum Proc. Florida State Hort. Soc. 103 370 372
Gilman, E.F., Yeager, T.H. & Kent, D. 2000 Fertilizer rate and type impacts magnolia and oak growth in sandy landscape soil J. Arboricult. 26 177 182
Hach, C.C., Bowden, B.K., Koplove, A.B. & Brayton, S.V. 1987 More powerful peroxide Kjeldahl digestion method J. Offic. Anal. Chem. 70 783 787
Jones, J.B. Jr, Wolf, B. & Mills, H.A. 1991 Plant analysis handbook. Micro-Macro Publ., Athens, GA
Kuo, S. 1996 Phosphorus, p. 869−920. In: J.M. Bartels (ed.). Methods of soil analysis. Part 3. Chemical methods. Soil Sci. Soc. Amer., Madison, WI
Mills, H.A. & Jones, J.B. Jr 1996 Plant analysis handbook II. Micro-Macro Publ., Athens, GA
Shober, A.L., Moore, K.A., West, N.G., Wiese, C., Hasing, G., Denny, G. & Knox, G.W. 2013 Growth and quality response of woody shrubs to nitrogen fertilization rates during landscape establishment in Florida HortTechnology 23 898 904