Himalayan Blue Poppies, or Mecanopsis, one of the ultimate challenges for East Anglian gardeners, are currently in flower at Daws Hall in Lamarsh.
Major Iain Grahame said there was only two opportunities for people to see them this year.
This Sunday and Sunday, June 19, 1–5pm, the nature reserve and gardens will be open for charity.
Other attractions include pond dipping, a wildflower meadow and an observation bee hive.
Entry is £5 for adults, children £1.