Seed dispersal is a crucial process in most plant invasions, but is notoriously difficult to study. One technique to identify the maternal source of dispersed seeds and newly established seedlings is labeling with a stable isotope. We tested whether foliar application of ¹⁵N-labeled urea would result in sufficient ¹⁵N enrichment to discriminate among seeds and seedlings grown from those seeds of the invasive shrub Lonicera maackii (Amur honeysuckle). We subjected mature L. maackii to all combinations of three concentrations of ¹⁵N-labeled urea (0.025 g L⁻¹ [0.003 oz gal⁻¹], 0.20 g L⁻¹, and a 0 g L⁻¹ control) and three temporal treatments (one application in August, one application in September, and five applications spaced every three weeks from June through August). Seeds were collected September to November; some of these were analyzed for %¹⁵N and others allowed to germinate and grow into seedlings under two treatments (in potting mix in greenhouse and in woodlot soil outdoors). Seedlings were harvested midway through the next growing season. We found that seeds from plants subjected to the three different concentrations had significantly different %¹⁵N levels, and there was a significant interaction between concentration and temporal treatment: the highest seed %¹⁵N levels were from plants sprayed five times with ¹⁵N-labeled urea, and the second highest from plants sprayed once in September. Similar patterns in %¹⁵N levels were found in seedlings, except that those from the 0.025 g L⁻¹ spray treatment were only distinguishable from controls for seedlings grown outdoors in woodlot soil. These findings demonstrate that a single foliar application of ¹⁵N in early September is sufficient to label both seeds and seedlings of this invasive shrub, enabling one to identify the source of field-collected seeds or seedlings. This provides a tool for studying patterns and processes in seed dispersal of Amur honeysuckle and potentially other invasive plants.