He led development of the City of Belfast International Rose Gardens in collaboration with Sam McGredy IV and also began trials of new varieties in Sir Thomas and Lady Dixon Park in 1964. He founded the Rose Society of Northern Ireland and was Secretary (1964 - 1972) and then President (1988 - 2018). In 1978 Wallace made sure that Northern Ireland was included in the Britain in Bloom contests. He retired in 1988.
