Mahoney's unbridled enthusiasm for plants extended to included the objects and implements found in gardens - watering cans, greenhouses, wheelbarrows, spades etc. His interest and aesthetic sensibility were shared with his contemporaries Edward Bawden, Geoffrey Rhoades, John Nash and Evelyn Dunbar, withwhom he swapped cuttings by post. Mahoney was instrumental in helping Bawden layout his celebrated garden at Brick House, and Bawden in turn was asked to contribute the foreword to Mahoney and Dunbar's 1937 book Gardener's Choice. 

Elizabeth Bulkeley, the artist's daughter, recalls her father's passion thus: 

Beneath the south wall of his studio my father made wigwams of canes to support multicoloured gourds and deep blue Morning Glory trumpets. He grew many kinds of Polygonum. Some, like P. cuspidatum, were statuesque giants, others, were delicate and lacy. He appreciated flowers such as tulips and Opium Poppies for their slender upright form with a burst of bloom at the top, as they popped up between bushier plants throughout the garden. Lilies likewise shot through the foliage of other plants and exploded in exquisite flowers. Auriculas were a particular passion. He loved the primly formal arrangement which complemented the sumptuous colour combinations. (letter to Paul Liss 15th March 2005)