Pennisetum setaceum (Forssk) Chiov. is a perennial C4 bunchgrass native to North Africa that has become widely naturalized or invasive outside of its native range. It commonly grows in disturbed habitats, which may have high levels of soil phosphorous (P). While nitrogen (N) addition and mixed-nutrient addition have been shown to increase growth and flowering in P. setaceum, no previous research has directly tested the effects of elevated soil P. We used a nutrient addition greenhouse experiment to test the effects of elevated P and N availability independently and in combination. N-treated plants grew faster and larger, were less stressed (as measured by maximum quantum yield of photosystem II, F_V/F_M), flowered earlier, and produced more inflorescences than plants not treated with N. P-treated plants were significantly larger compared to controls, but the difference in size was small. We show that N is the nutrient more strongly limiting the growth and reproduction of P. setaceum. We suggest that the affinity of P. setaceum to habitats of characteristically high P availability may reflect other, similar characteristics of these habitats, such as high disturbance rates.