Predispersal seed predation imposes fitness costs on plants, and is expected to contribute to selection on flowering phenology. Plants may evade predispersal seed predation by flowering early or late, or by flowering synchronously with conspecific neighbours to satiate the seed predators. While the first strategy leads to prolonged flowering, the second strategy results in distinct flowering peaks. Further, the number of neighbours may influence the optimal phenological strategy. We tested the seed predator–satiation hypothesis in different patch sizes in a field experiment with the white campion, Silene latifolia (Caryophyllaceae). In its native, European range, the white campion is heavily attacked by the seed predating and pollinating moth Hadena bicruris (Noctuidae). In a fully–crossed, two-factor design, we transplanted arrays of plants of different age classes to 24 sites. We measured realized synchrony, fruit predation, flower/fruit abortion and seed set/fruit. Plants suffered more fruit predation in synchronous small patches. In combination with higher abortion in small patches, plants in synchronous small patches produced fewer undamaged fruits. Within patches, individual plants that flowered more synchronously with their neighbours suffered increased fruit predation but aborted fewer flowers or fruits. These results refute the idea that synchronous flowering evades seed predation in this species, and suggest instead that synchronous flowering increases patch attractiveness to seed predators and possibly pollinators. However, no advantage of either synchronous or asynchrounous flowering was apparent in large patches, indicating that selection pressures on flowering phenology through biotic interactions strongly depend on patch, and thus population, size.