Hall's training at Kew was complete by 1933, whereupon he became curator of the succulent plant collection at
Alexandra Park, Manchester. His consuming interest in South African succulents led to some 600 species being added to the collection. During
WWII he spent four years with the
Royal Air Force, at the end of which he contacted
Robert Harold Compton, director of Kirstenbosch in South Africa, inquiring about the possibility of a position there. A post was created especially, and Hall arrived with his wife and 12-year-old son in August 1947. Starting with a very small succulent plant collection, Hall improved its stature to one of world renown by the time of his death. '') in the Kogelberg mountains He organised some 140 exploration and collecting trips throughout southern Africa, often accompanied by fellow collectors. Compton from Kirstenbosch, Reynolds the
Aloe authority, Bernard Carp, nurseryman and patron for some collecting trips, Ted Schelpe, professor and curator of
Bolus Herbarium at
University of Cape Town, Leonard Eric Newton, from
Kumasi University in Ghana, and
Gordon Douglas Rowley, horticulture and botany lecturer and author from Reading University. His travels took him through
Kogelberg Nature Reserve, during which time he stayed in
Gordon's Bay. He also travelled through what is
Addo Elephant National Park, examining the flora, as well as
Camdeboo National Park,
Augrabies Falls and the
Waterberg Biosphere. He was competent with both pencil and camera, illustrating his numerous contributions to the 'National Cactus and Succulent Journal' and other journals. He produced a small Longman's field guide 'Common Succulents' in 1955 illustrated by
Elsie Garrett Rice, and collaborated with
Harriet Margaret Louisa Bolus (1877–1970) on the
Mesembryanthemaceae. Harry Hall's second marriage was to Lisabel Irene Booysen, a fellow botanist who had graduated from the
University of Pretoria. She had worked for the CSIR, been employed by the University of Pretoria in their Department of Plant Physiology and had been a school teacher before moving to Cape Town and Kirstenbosch, where she met Harry. He became a member of the '
International Organization for Succulent Plant Study' in 1953, and received the '
Cactus and Succulent Society of America' Fellow award in 1981. He is commemorated in the genus
Hallianthus, and in numerous succulent specific names. ==Associates==