Hertfordshire is just north of London and has a number of great estate gardens which belonged to powerful families. The most important of these gardens is Hatfield House Garden. It has the finest late-renaissance garden in Hertfordshire and perhaps the finest in England. Also, at Ashridge, Hertfordshire has a fine example of Humphry Repton's garden design theory. St Paul's Walden also has an important place in garden history, as an example of the Forest Style (occupying a transitional place between the Baroque and Landscape styles of garden design).
Salvo Fair is an annual exhibition and sale of garden antiques, architectural salvage and reclaimed building materials that takes place at Knebworth House at the end of June. The dates for 2010 are June 26th and 27 June (open 11am to 4pm, cost £8 including admission to Knebworth Park).