Kosteletzkya pentacarpos (L.) Ledeb. (seashore mallow) is recognized as an important plant species for several industrial applications, especially in North America and Asia. In Europe, seashore mallow is highly threatened and subject of conservation actions (e.g. reintroduction). In order to define appropriate multipurpose cultivation protocols, suitable for biomass production and for conservation purposes, we investigated the effect of varying levels of soil salt content and nutrient availability on seashore mallow. As expected, seashore mallow had the best performance in terms of growth rate, flowering and fruit production when fertilization was applied, while salt had only limited effects. Interestingly, seeds produced by fertilized plants showed a lower germination performance and higher mortality than seeds developed form control and non-fertilized plants. Our results highlight a trade-off between parental plant growth and seed performance, the former being enhanced by fertilizer addition and the latter being reduced by fertilization. The causes of this tradeoff are related to a transgenerational maternal effect of fertilizer that has important implications for seashore mallow cultivation. From a practical point of view, biomass production benefits from fertilization but if the quality of seeds and the fitness of the next generation are major objectives (e.g. seed production and species conservation), fertilization is not recommended.