They had both travelled extensively in Europe during their studies of medicine. It is known that Sibbald met and stayed with the great Scottish gardener Morrison in Blois at the garden of the Duke of Orleans.
Sibbald described this in his autobiography:
"I had from my settlement here in Edinburgh a designe to informe myself of the natural history this country could affoord, for I had learned at Paris that the simplest method of Physic was the best, and these that the country affoorded came nearest to our temper, and agreed best with us. So I resolved to make it part of my study to know those animals, vegetables, mineralls, metals and substances cast up by the sea, were found in this country, that might be of use in medicine, or other artes usefull to human lyfe."
Sibbald and Balfour were friendly with Patrick Morray, Laird of Levingstone (now Livingston). Morray was a keen gardener, who with other gardeners throughout Europe, exchanged seeds and information (Patrick Morray died of a fever in Avignon (1671) during a long tour of Europe (1668-71) on his way to Italy). Sibbald and Balfour visited Levingstone to admire his collection of nearly a thousand plants. This gave rise to the plan to establish a medicine garden in Edinburgh .
In 1671, "Doctor Balfour and I first resolved upon it, and obtained of John Brown, gardener of the North Yardes in the Holyrood Abby, ane inclosure of some 400 foot of measure every way. By what we procured frorn Levingstone and other gardens, we made a collection of eight or nyne hundred plants ther'."
The purpose of the garden was to supply fresh plants for medical prescriptions and to teach medical botany to students. The garden was looked after by James Sutherland (1639-1719) who later became the Professor of Botany in the Town's College. Balfour and Sibbald were appointed Visitors to the Garden.In 1676, it was obvious that the garden was too small so Balfour leased from the Town Council a second garden which belonged to the Trinity Hospital. The site of this garden can be found by platform 11 in Edinburgh Waverley Station, where there is a commemorative plaque. In 1763 the garden moved to an expanded site near Gayfield Square to the west of Leith Walk and then in the early 1820s it moved to the present site in lnverleith Row. The garden is the second oldest surviving in Britain after Oxford (1632) and ranks in importance with Chelsea Physick Garden (1673) and Kew (1759).