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.
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ShoberA.L.MooreK.A.WestN.G.WieseC.HasingG.DennyG.KnoxG.W.2013Growth and quality response of woody shrubs to nitrogen fertilization rates during landscape establishment in FloridaHortTechnology23898904