Biomass.   The major factor affecting time of biomass accumulation for peppermint is the method of rust control (flaming vs. chemical control).  Peppermint that is flamed produces biomass over a shorter growing season than fields where chemical rust control is used.  Fields flamed for rust control begin harvestable biomass accumulation approximately 30 days later than unflamed fields. Vigorously growing fields where chemical control is used produce more biomass than fields that are flamed. Peppermint growth follows a similar pattern when either method of rust control is used, producing between 8,000 and 10,000 lb dry matter/acre.

N Uptake. Peppermint that is flamed accumulates N at a faster rate than fields where chemical control of rust is practiced. However, both techniques produce plants at harvest with approximately the same amount of N, 170 to 250 lb/acre.  Flamed and unflamed peppermint have different N uptake rates. Flamed mint has a maximum N uptake rate of approximately 3 lb/acre/day, while the maximum N uptake in unflamed mint is about 1.5 lb/acre/day. The peak N uptake period is between June 15 and July 15.

Management. Nitrogen fertilizer rates of no more than 200 to 250 lb/acre are necessary for adequately irrigated mint. N can be supplied through the irrigation water or to the soil early in the growing season. Supply approximately 175 lb/N/acre before mid-June where peppermint is flamed or by mid-May where chemical rust control is used. N applied in late July or August is likely to remain in the soil after harvest.