Plants could be protected by being grown on a south facing wall to encourage longer flowering. There were also a range of glass houses where roses like 'Dr Grill' could have been used for cut flower. Don't believe everything you read about Robinson's "naturalistic" way of gardening, he was a lot more formal in reality. After Robinson's death the garden went through a period of neglect for over twenty years, especially during the war and apart from mature trees very few of the original plantings remained. There were still pictures by Moon in the House when Peter Herbert took on the lease and restored the garden and converted the house into a hotel but they were sold.
Working at Gravetye was an experience but due to lack of money and staffing problems not a really enjoyable one. My previous job working at Charleston Farmhouse, country home of Vanessa Bell and Duncan Grant was far more interesting...