Effects of Nitrogen Rates on Plant Performance and Nutrient Content in Reblooming Iris

For its fragrance and showy display with multicolors, Iris germanica has great potential to serve as a specialty cut flower. Some cutivars of Iris germanica have the potential to rebloom in one growing season. However, limited research has been conducted concerning nitrogen (N) fertilizer guideline for these reblooming cultivars. The objective of this research is to investigate the optimal N management practices for promoting blooming performance of reblooming iris. The study was initiated in Spring 2012, using ‘Immortality’, a reliable reblooming iris cultivar, as the research material. Plants were grown in 1-gallon containers and treated with one of five N fertigation rates (N at 0, 5, 10, 15, or 20 mM) during the growing season. Results showed that higher N fertigation rates not only accelerated plant growth rate, but also promoted earlier first bloom and increased the number of flower stalks at second bloom. Plants received N at 0 and 5 mM rates did not produce any second bloom. Plants treated with N at 20 mM produced the most number of stalks at second bloom. The tissue nutrient analysis results showed that the N concentrations in root and rhizome in Winter 2012 increased with increasing N fertigation rates. The growth data in early Spring 2013 showed that plant height and number of fans per plant increased with increasing N fertigation rates in 2012. Results from this study suggested that increasing N fertigation rate can increase plant nutrient concentration and improve plant growth and blooming performance. Plants treated with N at 20 mM have the potential to produce the most number of flower stalks.