Thus. if the definition of a garden is based on a matter of the scale of cultivation - gardening as supposed to agriculture - then the first gardens were the made by the Neolithic tribes people who gave up hunter gathering, domesticated wild cereals and adopted a sedentary, agrarian lifestyle. The oldest of such sites so far discovered by archaeologists is Tell Aswad in what is now Syria, where ‘the earliest systematic exploitation of domesticated cereals (emmer wheat) dates to c. 9000-8500 BC’.
However, I am not aware of archaeological evidence to support the claim of Neolithic ornamental gardens - if its there I would love to discover the source. But I am sure that domesticated plants would have been grown in a protected proto-garden, and as we all know an arrangement of plants grown for utility can simultaneoulsy have an ornamental value.
If, on the other hand we are talking about ornamental gardenis, then the Sumerians (c.5000-2400 BC) had hunting parks which were used for recreation and pleasure, but were not gardens for a garden’s sake.
And, as already mentioned in a post there is archaeological evidence from Crete that the Minoans may have made gardens - there are frescoes from the Villa of Amnisos and a possible rock garden at the Place of Phaistos, both dating to c.1500 BC.