Container-grown Herbaceous Perennials:
Response to Fertility and Water
Peter Conden, Stuart Warren, and Robert Lyons

Herbaceous perennials have grown to be a major factor in nursery production over the last decade. More and more nursery owners are reaping the benefits of this fast growing, low input crop. Despite this rise in popularity, very little research has been reported regarding nutrition and irrigation requirements of perennials. Many growers follow fertilizer company recommendations or past experience in woody plant production. In an effort to establish guidelines for nutrition and irrigation procedures for production of container-grown herbaceous perennials, the following study was undertaken.
On June 1, 2002, 3 species (Hemerocallis ‘Aztec Gold’, Coreopsis grandiflora ‘Early Sunrise’, and Santolina chamaecyparissus) were potted into 1 gal containers utilizing a medium of 8 pine bark : 1 sand (by vol), amended with 2 lbs/yd3 dolomitic limestone and 0.5 lb/yd3 granular surfactant (Aqua-Gro G, Scotts Co., Marysville, OH). Fertilizer treatments were incorporated into the medium prior to potting, and consisted of a 5-6 month controlled-release (CRF) (Polyon 16N-5P-10K with minors, Harrell’s Sylacauga, AL) After potting, the plants were placed on a gravel pad at the NCSU Horticultural Field Laboratory, Raleigh. The plants were subjected to four rates of controlled-release fertilizer and four irrigation volumes delivered through individual spray stakes. The CRF treatments were 8, 11, 14, or 17 lbs/yd3 (the labeled low, medium, and high rates were 8, 12, and 16 lbs/yd3). The irrigation treatments were 40, 80, 120, or 160% of available water (AW) per container [(AW = 24 oz (720 ml)], applied cyclically at 11:00 am, 1:00 pm and 3:00 pm daily. The experimental design was a randomized split-split plot with irrigation as the main treatment, species as the split plot treatment, and fertilizer rate as the split-split plot treatment.

Results and Discussion
Fertilizer rate had no significant effect on shoot dry weight, root dry weight, or visual rating across all irrigation treatments and species. Nutrient content of plant tissue was significantly affected by irrigation and fertilizer treatment, indicating that plants were taking up nutrients up to luxury consumption levels. Nearly all plants had visual ratings of 4 or 5 out of 5, indicating a full, lush, saleable plant.
All plants except Coreopsis that received 80% available water had leaching fractions (LF) of ≈20%, which is recommended for growing woody plants (Coreopsis needed 160% available water to reach 20% LF). However, there were no few differences in growth among all irrigation treatments.
This study indicates that the labeled rates for CRFs are too high for producing saleable perennials, and water requirements are lower than we expected. This will add up to tremendous economic as well as environmental savings in terms of water and fertilizer usage. Because these results were somewhat surprising, this study will be repeated in 2003 with lower rates of fertilizer and water. The 2003 study should allow us to develop fertilizer and water recommendations for production of container-grown herbaceous perennials.

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