Sir John Eardley-Wilmot became the Governor of Tasmania in 1843 and with the appointment came the responsibility for the Botanical Gardens which were suffering badly after ten years of neglect following Davidson's departure. Complaining of a lack of funds, he called several meetings of the Tasmanian Society, which at the time loosely oversaw the operations of the Gardens. He seemed to have had a gift for antagonising the more influential members of the community, many of whom withdrew from the Tasmanian Society, to the detriment of The Gardens.
The monument to his tenure is seen in the 4-metre-high convict-built brick wall which stretches 280 metres north–south across the Gardens, supported by numerous buttresses. It also extends in an east–west axis and finishes to the rear of the Superintendent's Cottage. The use of convict labour for this project, when unemployed free men were available, caused social unrest. The wall became the eastern marker for the border of the Gardens for many years and, for most of this time, contained only one opening towards its southern end.
In 1964, Government House donated 2.2 hectares east of the wall to The Gardens – the section that now includes the Japanese Garden and the French Memorial Fountain. As part of this process, five archways were made through the wall. The Mixed Border is planted along its western side.