A widower in 1974, Tredgold married his second wife, Mrs. Margaret Helen Phear (née Baines; 1910-2012), a widow and mother of three children, originally from Aliwal North, South Africa. Together the couple researched the folklore of Zimbabwe (then Southern Rhodesia) and published children's books based on them. They also researched edible plants, culminating in Food Plants of Zimbabwe, which she completed after his death and published in 1986.
A devout Roman Catholic, Lady Margaret died in 2012 at age 102 in England, where she had relocated in 2004 due to the Mugabe government's policies. She was predeceased by one son, and survived by a second son and her daughter, with whom she lived in England.