This study was initiated to establish critical N plant tissue levels for asparagus (Asparagus officinalis L.) during the fern growing season. Tissue samples for chemical analysis were taken from asparagus plants over three growing seasons. The experiment consisted of nine treatments with five levels of water ranging from 750 to 4200 mm·ha−1 and five levels of N fertilizer ranging from 100 to 655 kg N/ha. Only the cladophylls were sampled during the fern growing season beginning in mid-April and monthly through mid-September. Total N concentration at various sampling dates and spear yield were highly correlated. Total N concentration indicated the N status of the asparagus plant. Minimum or critical levels of total N were established for the fern growing season in the desert regions of Arizona.