The history of the Walled Garden almost certainly began well before 1830, when small-scale marl extraction created the ponds which later became a major feature of the Garden. Marl pits are shown on the 1829 Grappenhall Tithe Map in approximately the same places as they are found in the Walled Garden.
Marl is a calcium-rich deposit which is found under much of Cheshire and which, when spread over the surface, adds nutrients to the soil and raises its pH. As a handy by-product, it creates ponds which are useful for watering cattle.
However, spreading marl over large areas by cart is time-consuming and expensive, so it was often carried out from numerous small pits rather than large, central sites, leading to marl pits being dotted all over the Cheshire landscape – over 40,000 such ponds were recorded late in the 19th century, and it is fair to assume that there were originally more.