Fragmentation caused by disturbance is frequent in wetlands and usually co‐occurs with increases in cadmium and nutrient availability. However, whether fragmentation can interact with nutrients and heavy metals to affect wetland invasive plants has been little studied. We conducted a greenhouse experiment to test the effects of fragmentation (initial fragment was non‐severed, was severed into two fragments, and three fragments), cadmium (low, medium, and high), and nutrient availability level (high and low) on the growth of a widespread, invasive clonal plant Alternanthera philoxeroides (Mart.) Griseb. Clonal fragmentation reduced the total mass, stolon mass, root mass, and total stolon length of A. philoxeroides and altered the biomass allocation. Increases in cadmium adversely affected the growth of A. philoxeroides. The high level of cadmium increased leaf mass ratio but decreased stolon mass ratio. Response of leaf mass ratio to fragmentation varied at different cadmium or nutrient availability levels. Fragmentation, cadmium, and nutrients had a significant interaction on leaf mass ratio. Our results suggest that fragmentation can adversely affect the growth of A. philoxeroides. The adverse effect of fragmentation was greater at high nutrient levels and high cadmium levels (0.4 and 2 mg L−1).