If you haven't already discovered it, Piet Oudolf's website has information about his gardens and some downloadable plans.Sheffield University’s Landscape Department is a world focus for work on naturalistic planting design. Piet is very generous with enabling people to access information; he has made plans available here.

Professor James Hitchmough has his own site. Prof. Nigel Dunnett is also very active in this area, as well as being the UK’s leading green roof expert. 

Gardens to visit
I am often asked about gardens or parks to visit which reflect the ‘new perennial’ style of planting. Here are the best:
Sichtungsgarten Hermannshof. Weinheim an der Bergstraße, Baden-Württemberg . A nineteenth century villa garden in the centre of a pretty little town, open daily as a public park. A huge range of habitat-based plantings, small enough for domestic gardeners to relate to. Prairie-inspired drifts of perennials made by director Cassian Schmidt are of particular interest in late summer. Some of the most innovative and valuable research on planting design and maintenance is being carried on here. Open daily, all year, 10:00-18:00. Babostraße
Westpark, Munich . Pretty much the jewel in the crown. Vast, full of all sorts of joys and inspirations for anyone interested in public space. The most spectacular planting is the ‘steppe’ dry zone at the far western end. Open daily all year. Westendstraße/Hansastraße. U-Bahn Westpark
Sichtungsgarten Weihenstephan, Freising, Bavaria . Very much a plant collection and teaching garden but lovely none the less – in fact some very clever and subtle planting design. Great place to learn about perennials. Freising is a nice little town too, with fab Roccoco cathedral. Open daily, April – Oct. 9:00-18:00.

Kwekerij Oudolf, Hummelo, Netherlands . Piet and Anja Oudolf’s private garden and nursery. Perennial lovers are always in ecstasy, and even Roy Strong liked it – “wonky baroque” in his words. Website has details of garden openings.
Parks in Amstelveen – De Braak, Jac P. Thijsse . A fascinating and very long running experiment in native plant management, with a wonderful balance between nature and aesthetics. Open daily, all year.
Holbrook Gardens. Tiverton, Devon One of the best examples of ‘New Perennial’ planting in Britain, very much inspired by Hermannshof and other German plantings. Plenty of other interesting and experimental plantings too, with a very good nursery attached. Sampford Peverell, Tiverton, Devon EX16 7EN

Trentham Gardens. Work by Piet Oudolf and an expanding range of plantings by Nigel Dunnett. A very interesting development and a new model for commercial public space. An impressive Tom Stuart-Smith planting too.

Cambo House, Fife A striking and very enjoyable version of the New Perennial style. Head Gardener Elliott Forsyth has laid out extensive borders in the old walled garden based on a number of habitats and themes. Its design heritage is clearly continental Europe, but there is plenty of his own thinking too. Open daily, 10-5.

Jardin de Berchigranges in the Vosges mountains is incredibly beautiful and inventive, with many imaginative touchtes, wonderful planting, inspiring eco-architecture and some very innovative hard-scaping using wood where many might have used stone or cement. My kind of garden.

Northwind, a nursery and garden in southern Wisconsin, where Roy Diblik is in charge of perennial and wildflower production is a real centre of excellence for the Midwest. It would be a great garden even if it were in Gloucestershire. Roy is one of the most innovative and insightful of American gardeners.
Chicago's Lurie Garden and New York's Highline are well-known Oudolf creations. The One Drop at a Time project at 168, Elm Avenue, in the Chicago suburbs, is an innovative domestic scale rain garden developed by landscape architect Marcus de la Fleur.

I had some funding from an EU project in 2009-10, which enabled me to design a questionnaire to encourage gardeners to share information about long-term plant performance - issues like longevity, level of spread etc. I have written up a 'lite' version of the report in The Hardy Plant; you can see the full report. There is also a shortened version of the report in the June 2011 issue of The Plantsman. Also, I love to hear from anybody who might want to participate in future research.