Increasing concerns about nitrogen (N) runoff from nursery production have increased the need for fertilization practices that increase N use efficiency and decrease the potential for environmental contamination without affecting crop productivity or quality (Yeager et al., 1993). To optimize N fertilizer management in hydrangea production, knowledge of how rate and method of N fertilizer application influence plant performance is essential. Published literature on N use (optimum amount, application timing, and method) in production of container-grown florists’ hydrangea (Hydrangea macrophylla) is minimal (Bailey, 1989; Dirr, 2004). Most research on hydrangea nutrition has been focused on how fertilizer influences sepal coloration (Bailey, 1989; Dirr, 2004; Midcap, 1998).
To produce florists’ hydrangea, many growers transplant rooted cuttings into 10 to 20 cm diameter (400 to 3100 cm3 volume) pots commonly applying liquid fertilizer with 100 to 175 mg·L−1 N at each irrigation or 340 to 450 mg·L−1 N every 7 to 10 d during the vegetative stage of production (Bailey, 1989). Plants are normally manually defoliated late in the growing season, stored in a cooler for 6 to 8 weeks, and then placed into the greenhouse for forcing. During the forcing stage, plants are normally supplied with liquid fertilizer containing 150 to 250 mg·L−1 N at each irrigation or 340 to 450 mg·L−1 N every 7 to 10 d during forcing (Bailey, 1989).
High-quality florists’ hydrangea plants are usually full and compact in height. Chemical growth retardants are normally applied during the vegetative stage and the early period of forcing to control plant height (Bailey, 1989). An improved understanding of plant N requirements during vegetative and forcing stages of production would assist growers of florists’ hydrangea in developing more efficient N fertilization practices using potentially less N and growth retardants.
In many species, leaves can contain up to 50% of the total N in a plant in late summer and early fall (Bi et al., 2007; Forshey, 1963). In deciduous plant species, ≈50% of the N in leaves moves from the leaves into stems and roots before natural defoliation (Kang and Titus, 1980; Shim et al., 1972; Spencer and Titus, 1972). The plant uses this stored N for new growth during the next growing cycle (Millard, 1995). Manual defoliation of florists’ hydrangea before cold storage can help prevent the occurrence of diseases, especially botrytis bud rot (Bailey, 1989). However, because plants are usually defoliated when leaves are green, before N movement from leaves, they can lose a significant amount of N. This decrease in stored N could potentially result in poor growth or plant performance during forcing.
Foliar fertilization in the fall is considered an alternative to supplying N to the soil of woody perennial nursery plants. Spray application of urea to deciduous plant species after terminal bud set increases N storage without stimulating new growth or delaying dormancy development (Bi et al., 2003; Cheng et al., 2002; Oland, 1960; Sanchez et al., 1990) and has the potential to decrease groundwater contamination resulting from soil nitrate leaching (Embleton et al., 1986). Based on the benefits reported for other species, spraying florists’ hydrangea with urea before manual defoliation could potentially decrease overall N fertilizer input during production while maintaining or improving plant quality.
The objectives of this study were to determine: 1) how rate of N application during the vegetative stage of production influences plant growth; 2) whether plant N content before cold storage influences plant growth and flower development during forcing; and 3) whether urea sprays in the fall increase N storage before cold storage and plant growth and flower development during forcing. Our goal is to develop a fertilization program that reduces excessive vegetative growth and improves flowering performance of container-grown florists’ hydrangea without causing nutrient deficiency or reducing plant quality.
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