Evening primrose plants were fertilizer with different nitrogen applications, 0, 80, and 160 kg per ha. These applications produced plant morphology changes: leaf area index, dry matter, harvest index and yield. Leaf area index was higher for the 160 kg/ha application during the flowering differentiation, stem elongation and flowering phases. Dry matter production was also affected by the nitrogen applications. The 0, 80 and 160 kg/ha of nitrogen produced 1,247, 1,487 and 1,793 g/m², respectively of total dry matter. Yield was also affected by the nitrogen applications, the lowest concentration produced 118 g/m², while the 80 and 160 applications increased seed production to 158 and 228 g/m². Harvest index observed for these nitrogen fertilizations were 0.087, 0.109 and 0.119, also respectively. Nitrogen fertilizations increased dry matter and yield due to the production of more leaf area since the early phases and the duration of this area. And also, nitrogen applications increased the transformation of dry matter into more seeds.