Abstract:In Puerto Rico, oranges made up $6,452,000 of the agricultural gross income for 2014-2015. Today, citrus greening (CG) is the most aggressive disease affecting the citrus industry in the whole world. This disease causes dieback of the plant, among other symptoms, which is resulting in the reduction of citrus trees in the field across the world. Currently, it is recommended to grow citrus rootstocks in nurseries to produce disease-free trees. The objective of this investigation was to evaluate (before and after grafting) the effect of different substrate mixes and quantities of fertilizers on the rootstocks Carrizo citrange and Swingle citrumelo in order to accelerate their development inside of a protected structure. The treatments were: Promix + sand (control) (1:1), Promix + sand + coco peat (1:1:1), Promix + sand + coffee compost (1:1:1) and Promix + sand + rice husk (1:1:1). Two 18-6-2 fertilizer treatments were also evaluated: 5.6 g and 8.5 g. The substrate that contained 33% rice husks negatively influenced every parameter evaluated for both rootstocks. Carrizo presented better development on the coffee compost mix, while Swingle did not exhibit significant differences among any substrates, except on rice husk, for most of the parameters. "Rhode Red Valencia" presented better results for dry weight when grafted on Carrizo with the coffee substrate. The rice husk substrate is not recommended for the citrus tree production at the nursery level.