Defining Leaf Tissue Nutrient Standards and Nutrient Disorder Symptomology of Greenhouse-grown Spearmint (Mentha spicata L.)

Spearmint ( Mentha spicata L.) is a perennial herb popular for its distinct flavor and aroma. While traditionally grown outdoors as a field crop, controlled environment agriculture can provide an alternative method for producing spearmint. The objective of this study was to define foliar mineral nutrient interpretation ranges specific to greenhouse-grown spearmint by inducing and documenting individual nutrient disorders. Plants were cultivated in a hydroponic sand culture system and supplied with a modified Hoagland’s solution, in which individual nutrients were either omitted or supplemented, while maintaining all others at consistent levels. As nutrient disorders became evident, symptoms were photographed and documented. Plant tissue was collected to measure plant dry mass and nutrient concentrations. Additional foliar tissue data were compiled with those from the present study to create a larger data set containing 315 samples. Data were analyzed to define interpretation ranges for 12 essential nutrients using a hybrid meta-analysis sufficiency range approach, which defined ranges for deficient, low, sufficient, high, and excessive tissue concentrations for each nutrient. The most representative distribution for each nutrient was selected based on the lowest Bayesian Information Criterion value. Potassium, calcium, sulfur, boron, and copper were best modeled using a normal distribution, while magnesium was best represented by a gamma distribution. A Weibull distribution provided the best fit for nitrogen, phosphorus, iron, manganese, molybdenum, and zinc. These findings provide previously unavailable resources for diagnosing nutrient disorders and evaluating foliar nutrient analysis of greenhouse-grown spearmint.