Irrigated agriculture depends on adequate and quality water supplies. As the level of salt increases in an irrigation source, the quality of that water for plant growth decreases. Crop plants are usually nonhalophytes that tolerate only moderate salt concentrations. Under salinity, they accumulate salt in their aboveground organs and, to a smaller extent, in roots. High salinity reduces plant growth and leaf area, which prejudices quality, especially in ornamental crops. The study of the behavior of ornamental plants that are tolerant to saline waters can be an advantage in areas with poor quality waters. The aim of this work is to study the influence of the fertigation water salinity on the nitrogen metabolism of Cordyline fruticosa var. ‘Red Edge,’ known as ti plant, Hawaiian ti, cordyline, or good luck plant. Four nutrient solutions with different electrical conductivity (EC) levels were applied: T1 (1.5 dS m), T2 (2.5 dS m), T3 (3.5 dS m), and T4 (4.5 dS m), obtained with the application of different amounts of sodium chloride (NaCl) to the fertigation water. As salinity increases, nitrogen concentration in leaves does not change, but it increases in roots. In leaves, nitrate reductase (NR) in vivo activity declines when salinity increases; when a substrate [nitrate (NO3 )] or a cofactor [molybdenum (Mo)] is added, NR activity increases. Potential NR activity (NO3 + Mo) shows no significant differences between treatments; this indicates that NR synthesis is not affected by salinity. So, the diminution of the NR in vivo activity suggests a NO3 and Mo level metabolic imbalance. In roots, Mo is more restrictive of the NR activity than the NO3 substrate level. There are more amino acids in T1 than in T4, but it seems that there are no significant differences in T2 and T3. No significant differences are observed in the protein content; this indicates that amino acid diminution is due to the maintenance of the protein content. In conclusion, it can be said that the increased activity of NR in roots may constitute part of an adaptation strategy of the plant to an increasing salinity in the growing medium.