Magnesian limestone grassland is the rarest limestone grassland community in the United Kingdom, with many sites having been lost to quarrying and urban development. Its reestablishment, and that of many other semi-natural grassland habitats, can be enhanced using seed collected from established communities. However, few studies have evaluated the effectiveness of methods of seed harvesting. The objectives of this study were to (1) test the effectiveness of a hand-held vacuum harvester in the collection of an adequate quantity of seed, and range of species, to revegetate former quarries and (2) determine the optimum time for seed collection based on a phenological study of the plants at the donor site. Germination tests of harvested seed were used to identify species, based on the germinating seedlings. Thirty-six species were identified, with Briza media (quaking grass) and Festuca sp. (red and sheep's fescue) being the dominant species and accounting for 74% of germinating seedlings. Species composition of vacuum-harvested seed was compared with species composition of the vegetation found in the principal donor site. The most common species in the collected seed were also common at the donor site, but some characteristic species of the grassland were absent or did not germinate. Most species reached a peak in ripe seed production between mid-August and early September. Although having several advantages, vacuum harvesting will not, by itself, provide either sufficient quantity of seed or the wide range of species often required. Suggestions are given for combining this technique with other methods.