2005. Nutrient diagnosis of Christmas tree needle greenness. Can. J. Plant Sci. 85: 939-947. Christmas tree (Abies balsamea L.) fertilization is generally guided by needle colour or chemical analysis. Our objective was to develop critical values for the traditional critical nutrient range (CNR) and the compositional nutrient diagnosis (CND) of Christmas tree needles for the Quebec Appalachians. We collected survey specimens (n = 174) and obtained a validation dataset made up of 10 paired dark green and pale green stands. The compositional simplex for CND comprised five nutrient concentration values (N, K, P, Ca, and Mg) and a filling value R 5 computed from differences between the whole tissue composition (i.e., 1000 g kg-1) and the known nutrient concentration values expressed in g kg-1. Nutrient multi-ratios were computed as the natural logarithm of the ratio of one nutrient concentration value to the geometric mean of all nutrients and the R 5. Nutrient indexes (I N , …, I R5) were computed as standard variables using the mean and the standard variation of nutrient multi-ratios for the high-greenness sub-population. A nutrient imbalance index, CNDr 2 , was computed as the sum of squared CND indexes. Needle colour was assessed using a colour chart and a SPAD-502 chlorophyll meter. The critical SPAD value was set at 48-50 for a high greenness rating in the survey dataset, and the high-greenness sub-population comprised 95 specimens. Nitrogen and P concentrations were highly correlated to each other. Critical concentrations were found to be 17.8 g N kg-1 , and 1.8 g P kg-1. CND diagnosis of the validation dataset was similar to CNR, but CND classified nutrients in the order of their limitation to colour rating. Using the validation dataset, critical values were 17.2 g N kg-1 and-1.015 as I N. The validated critical CNDr 2 for five nutrients (N, K, P, Ca, and Mg) was 12.6, which was close to the critical CNDr 2 value using the survey dataset (11.6) and to the theoretical χ 2 value of 11.1 (P < 0.05). Key words: Tissue analysis, nutrient diagnosis, chlorophyll index, nutrient imbalance index Parent, L. E., Khiari, L. et Pettigrew, A. 2005. Diagnostic nutritif de la verdure des aiguilles chez le sapin de Noël. Can. J. Plant Sci. 85: 939-947. La fertilisation du sapin de Noël s'appuie sur la couleur et l'analyse chimique des aiguilles. Notre objectif était de développer des valeurs critiques CND et d'intervalles critiques de concentrations chez le sapin de Noël dans la région appalachi-enne du Québec. Nous disposions d'un inventaire de 174 spécimens et d'un jeu de données de validation pour dix plantations appariées contenant des arbres vert foncé ou vert pâle. Le simplex de composition comprenait cinq concentrations nutritives (N, K, P, Ca, Mg) et une valeur de remplissage R 5 calculée par différence entre le tout (1000 g kg-1) et la somme des concentrations connues. Les indices CND (I N , …, I R5) étaient calculés comme des variables normalisées en utilisant la moyenne et l'écart type de la sous-population de spéc...