After the war, the park was initially used as allotments, before reverting to parkland. In 1960, the late Mr Roy Evison, OBE, VMH, Director of Parks and Gardens, designed and planted Withdean Park to hold a series of comprehensive plant collections that would tolerate a thin alkaline soil. These collections included viburrnam, hebe and rosa, with smaller collections of sorbus, quercus, fagus, flag iris and floribunda and old fashioned roses. These were all secondary to the main collection of lilacs, which were collected from all over Europe. In 1982, when Mr M Griffin was Director, this Collection was designated as a National Lilac Collection by the National Council for the Conservation of Plants and Gardens (NCCPG). Cut material from the collection was used at the NCCPG's Chelsea Flower Show display in 1985 and was awarded a Banksian Silver Gilt Medal. The quality of the collection was acknowledged by the International Lilac Society in May 1986 when Brighton Council was presented with the President's Award. At this time, the collection numbered over 270 shrubs. However, subsequently there was a decline in the standard of upkeep of the lilac collection. Job cuts and massive reorganisation left little time or money for 'hands on horticulture' such as propagation, labelling, maintaining and mapping the Collection.
In 1987, following the hurricane, vast numbers of trees were lost that had formed a shelter belt for the lilacs and at least 12 bushes were ruined and many damaged. Although the lilac collection was a scientific collection which needed a set budget and specific attention, this was not made available and only basic weed control and pruning were carried out. In 1993, following threats from NCCPG to remove the National status, concerted efforts were made to rescue the collection. In 1994, the plants were renumbered (584 individual plants) and work restarted on the curation of the collection. Many of the plants were showing signs of age and were much too tall to see the flowers. As recommended by Kew Gardens, they were pruned by chainsaw to invigorate them.
In 1996 Nottcutts Nursery undertook propagation, resulting in 900 young plants being raised at Stanmer Nursery, with a view to reviving the collection. Following publicity efforts by the Council, a meeting was held attended by 200 interested local residents, at which Director Mike Griffin and lilac specialist Phil Williamson asked the public for help to try and save the collection. The 'Friends' group was born.
Phil Williamson designed new beds only 4 metres wide with a staggered double row to make it possible to access the plants easily from the grass. To protect the bushes, especially the young ones, from rabbits, a fence was erected around part of the collection in 1999. Unfortunately, this effectively 'abandoned' about 172 plants in colour beds for which there was no documented information. Lilacs are officially allocated to one of seven colours from white to purple and, in addition to the 13 main beds, one bed of each colour had been planted originally.
The new beds were planted out in 2004. According to Phil Williamson, at this point there were 214 plants left from the original collection plus 159 from Denmark and 144 propagated from the original 1960 plants, making 719 plants of 320 different types on the site. As many people have been responsible for the collection since 1960, much documentation has been lost resulting in 'unknown' being a common name for plants in the collection.
As the site is exposed to the south west, the plan was that as the original bushes died off, the old beds would be used to create windbreaks by planting suitable plants that would also extend the flowering season of interest in the park. However, this was not done and in 2005 older lilacs were dug up and the beds grassed over.
As Withdean Park's National Lilac Collection was once of International importance, bearing comparison with other such collections world-wide (e.g Rochester in New York) we felt strongly that our City of Brighton and Hove should look after such a collection. The Friends of Withdean Park were approached in 2007 by the NCCPG who said the Collection was in such a poor state that it might lose its National status. The Parks Department were still under financial constraint and the Collection had been neglected, both in the park and at Stanmer Nurseries. We contacted local councillors, met with NCCPG representatives and liaised with the Parks Department Managers. However, at the end of 2007 the status of the Collection was reduced to 'provisional'. Somehow funds had to be found to enable the Parks Department to reinstate the level of work on the Collection that was needed. In August 2009, the NCCPG finally decided the National status was to be removed.