Marion and I just spent a perfect summer evening at http://www.hitchinlavender.com, walking amongst the many varieties of lavender, with swallows and swifts swooping around us, and a hare lolloping in a nearby field. They are open daily, but also for the NGS in the evenings over the next few weeks, details here: http://www.ngs.org.uk/gardens/find-a-garden/garden.aspx?id=25537 .
We recommend a visit.
Hardy Plant Society Hertfordshire Group 