Nitrogen Rate, Irrigation Frequency, and Container Type Affect Plant Growth and Nutrition Uptake of Encore Azalea ‘Chiffon'

Encore azaleas are popular in the U.S. because of their multiple blooming seasons and good performance under full sun exposure in the southern region. They are members of the large Rhododendron genus having hundreds of species and varying nutrition requirements. This study was conducted to investigate the influence of nitrogen (N) rates (0, 5, 10, 15, 20 mM N from ammonium nitrate) and irrigation frequency (once or twice per day with the same total amount of water) on growth of Encore azalea plants grown in two types of containers: one is a conventional plastic container (GL 2800, Nursery Supplies^® Inc., Chambersburg, PA), and the other one is a paper biocontainer (Western Pulp Products Co., Corvallis, OR). Feasibility of using biodegradable paper containers as an alternative to traditional plastic containers in a one-year production cycle of Encore azalea ‘Chiffon’ was evaluated. Results showed container type significantly influenced plant daily water use (DWU) with plants grown in biocontainers having significantly greater DWU than those in plastic containers. Plants treated with higher nitrogen rates (10, 15, and 20 mM N) and grown in biocontainers had greater plant growth indices, total leaf area, and total root length than those in other treatment combinations. The interaction of irrigation frequency and nitrogen rate influenced flower number. Plants treated with 10 and 20 mM N and irrigated once a day had a significantly greater flower number than those in other treatment combinations. Nutrition levels in plant tissues were also significantly influenced by nitrogen rate and container type.