Nutrient deficiencies of perennials: Part 1 of 12

An introduction

Perennials are profitable crops because of their increasing popularity among consumers and landscapers. They have subsequently become an important component of both greenhouse and nursery crops. In 2005, USDA Floriculture Crops Summary reported wholesale sales of perennials were $708 million, up 3 percent from the previous year. With the popularity of perennials has come increased demand for production information.

Fertility monitoring and management for herbaceous perennials requires balancing the plants’ requirements. Growers must monitor and manage the root substrate pH and electrical conductivity and provide adequate, but not excessive, levels of essential elements. Some general recommendations exist, such as controlled-release fertilization programs with liquid fertilization programs as a nutritional supplement for moderate to heavy nutrient-requiring plants.

Hardy perennials have been studied by researchers at Virginia Tech University in Blacksburg, while scientists at University of Florida in Milton have investigated tropical perennials.

In general, herbaceous perennials have lower nutritional requirements than rapidly growing bedding plants. This is especially true for hardy perennials. In fact, too much fertilizer can result in a smaller plant, delayed flowering and stunted root growth.

Causes of nutrient deficiencies

Nutrient deficiencies can appear quickly in a crop and reduce profit by affecting marketability. There are several factors that can impact the nutritional status of perennials.

Improperly working equipment. An improperly working fertilizer injector/proportioner can result in either a deficiency of multiple nutrients or (even worse), an “overdose.” Calibrate injectors weekly to maintain the desired level of delivered nutrients.

Overwatering. Constant saturation of the growing medium can lead to macronutrient and micronutrient deficiencies. As oxygen levels are inhibited by overwatering, root growth can be limited and water uptake slowed. Elements such as calcium are transported via waterflow, and deficiency symptoms can develop rapidly on new growth. The inactivity of root systems due to saturated conditions can lead to inefficient uptake of iron or phosphorus.

Low soluble salts. Soluble salts refer to the total dissolved salts in the growing medium at any given time and is measured in terms of electrical conductivity. When the electrical conductivity content of the root substrate is too low, plant growth is stunted and mineral deficiencies are observed. Low salts are usually due to application of too many clear-water irrigations. Deficiencies such as lower-leaf yellowing (nitrogen), lower-leaf purpling (phosphorus), and lower-leaf interveinal chlorosis (magnesium) are common when values are below 0.75 milli-Siemens per centimeter (PourThru extraction soil test method).

Mineral antagonisms. When certain elements are provided in excess to plants, uptake of other nutrients may be hindered. One example of a mineral antagonism is the nitrogen-potassium interaction, where for most herbaceous plants a 1 nitriogen:1 potassium ratio is recommended.

Excess phosphorus can cause a decrease in uptake of zinc, iron and copper. Other types of antagonisms are the potassium-calcium-magnesium interaction. Any one of these elements in excess can cause a decrease in the uptake of the other; therefore, a ratio of 4 potassium:2 calcium:1 magnesium is a good rule of thumb for perennial growers.

Cold temperatures. Temperature can also play a role in the occurrence of nutrient deficiencies. One classic example is the effect of low temperature (less than 55°F) on uptake of phosphorus in tomato. Purple coloration of the lower foliage is the common symptom. Many warm-loving species such as lantana can express phosphorus deficiency when grown too cool in spring.

Pathogens. Disease-causing organisms like Pythium feed on the nutrients in roots, causing an inefficient uptake of minerals. Iron deficiency (interveinal chlorosis of young foliage) can occur if root-rot pathogens infect the root system.

Foliar pathogens, particularly fungal organisms, can cause chlorosis of leaf tissue, which is a direct reflection of harvesting nitrogen from plant cells.

Water quality. Water quality can be a problem for some U.S. growers who experience high alkalinity (greater than 180 parts per million calcium carbonate), as it contributes to a high growing medium pH and subsequently insufficient micronutrient availability.

African bush daisy (Euryops pectinatus), dwarf creeping chenille (Acalypha pendula), and yellow shrimp plant (Pachystachys lutea) respond better to a low-pH (5.5 to 5.8) medium.

High alkalinity and a high medium pH (6.0 to 6.6) can lead to iron deficiency. To combat high alkalinity, growers apply acidic fertilizers such as 20-10-20 or inject acid into their irrigation water.

When there is little alkalinity in the irrigation water, crops may experience magnesium and calcium deficiencies. Pentas is known for its high pH requirement (6.0 to 6.6) and can develop iron and manganese toxicity symptoms if the root substrate pH is low.

Despite the increase in both the number of growers producing perennials and the number of species grown, little information has been published regarding their mineral nutrition requirements, specifically nutrient foliar standards and nutrient deficiency symptoms. Most nutrition research has focused on bedding plants and vegetative annuals, leaving growers, researchers and commercial laboratories to rely on past experience or adapt recommendations from other floriculture crops. This approach may result in excessive or insufficient fertilization and misdiagnosis of nutrient disorder symptoms.

Many perennial nutrient deficiency symptoms such as necrotic flecking, bronzing, leaf distortion and chlorosis are often mistaken as damage from pests and/or pathogens. University plant pest and disease clinics frequently find themselves trying to interpret and diagnose nutrient deficiencies and toxicities.

We have ongoing studies that induce nutrient deficiencies by growing plants in hydroponic systems while withholding one of the essential elements from the nutrient solution.

With the enormous variety of herbaceous perennials in commercial production, species were chosen that are both widely grown in their respective climates and also reasonably representative, physiologically speaking, of either several species in the genus or family subgroups.

- James Gibson and Holly Scoggins

James Gibson is assistant professor, University of Florida, West Florida Research and Education Center, Institute of Food and Agricultural Sciences, 5988 Highway 90, Building 4900, Milton, FL 32583; (850) 983-5216, Ext. 103; jlgibson@ifas.ufl.edu. Holly Scoggins is associate professor, Virginia Tech University, Department of Horticulture, 301 Saunders, Blacksburg, VA 24061; (540) 231-5783; hollysco@vt.edu.

The authors thank Fred C. Gloeckner Foundation for grant support, Smithers-Oasis for propagation medium, Yoder-Greenleaf, Hatchett Creek Farms and Emerald Coast Growers for plant material, and Quality Analytical Laboratories for tissue analysis. The authors also thank Velva Groover, Allison Byrd, Jude Groninger, Susan Haddock, Kim Strickland, Sharon Wombles and Kathryn Campbell for technical assistance.