Knowing what you’ve got

We make an estimate of the weight of seed we have for each species:

  • We weigh the sample to the nearest gram and then estimate how much of the sample is seed and how much is other plant material. This is quite approximate as, for example, grasses have other dried flower parts that look like seed and are hard to separate
  • Once we have an estimate of seed weight, we can then get an approximate figure for the number of seeds. We calculate seeds per gram from the 1000 seed weight figures in the Seed Information Database on the Millennium Seed Bank Project website (Royal Botanic Gardens Kew, 2016)
  • This information helps us:
    • Estimate our drilling rate in kg seed/ha and number of seeds per  square metre. The last collection we made had about 1 million seeds per kg and was drilled at 0.5kg per ha (or about 50 seeds per square metre)
    • understand why some species are doing better than others in the early years of grassland development
  • The number of seeds per gram for species we’ve collected varies from about 70 (Agrimony) to 33,000 (Meadow Saxifrage). Orchid seeds are much lighter – Common Spotted Orchid has about 500,000 per gram. We therefore exclude orchids from our seed rate calculations
Weighing garlic mustard
Weighing garlic mustard