I am often asked how to keep tall bearded foliage from deteriorating during the heat of summer. My response usually infers that low summer moisture is the major contributor to unattractive iris foliage.
Like most perennials, the energies expended by the iris plant to produce its annual flush of bloom leaves the plants with spent foliage and untidy plants. This life cycle results in scraggly plants that all experienced gardeners expect.
Possibly the most important time to nurture tall bearded iris plants is immediately after bloom. (The general advice for iris gardeners to fertilize in early spring before bloom seems to create more problems here than I care to subject my plants to!) My soil is sandy clay and I either fertilize my plants when planting in September orimmediately after spring bloom, always with a serious application of ammonium nitrate. (Living in an area previously dotted with phosphate mining fields, soil test results taken here usually reflect high levels of phosphorous.)
Many iris growers tend to keep their plants on low nitrogen diets. Here in the Nashville area, we always have about 4 to 6 weeks of very hot and miserably humid weather. These “dog days of summer” usually arrive in early to mid July and continue through mid to late August. (Keep in mind that I am growing my plants commercially in rows that may at any time be cultivated. I also transplant (dig and replant) every September.
Although I consider my plants to be well fed, by mid July they are often ready for some limited feeding. As the plants begin to look a bit tattered, I mix 2 Tablespoons of “Miracle Grow” and 2 Tablespoons of Consan (or a fungicide of your choice) per gallon of water. This is applied as a foliar spray using a pressurized garden sprayer. Within days of application, the plants quickly exhibit deeper green coloration and slough off unsightly outer leaves. If there are plants that do not respond to this treatment, I might follow up with a foliar spray of Epsom Salts and water and (more often than not) the greening response to this spray might indicate possible level(s) of magnesium deficiency.
I do not enjoy weeding in the miserable heat of summer. Thorough weeding immediately after bloom season makes any summer maintenance program run more smoothly. Serious gardeners spend little time “wishing” for a lovelier garden – rather, they work with diligence and discipline.
The final part of this equation is soil conditioning. I have had success incorporating leaves and peat moss. The quantities I use have led me to consider the cost effectiveness of baled straw. At least 3 inches of “loosened” straw is scattered into planting rows atop hefty ribbons of ammonium nitrate granules. Ideally, these two materials are tilled into the soil after at least 2 inches of rainfall; I prefer that this be completed 4 weeks before planting.
Year 2003 marked my 41st continuous year of growing tall bearded iris and I have practiced soil rotation whenever feasible. To expect reasonable plant performance in poor, tired and worn soil is courting wreckless fantasy. Plants need and will generously respond to proper feeding with a sensible plan of nutrition and reasonable care.