One of the difficulties of early garden history (pre-nineteenth century) is the lack of documentation. It is not simply the passage of time, though that is part of it...gardens were considered a well-known fact of life and in many cases simply not given the importance of the house, which was often well-catalogued and described. One of the places to look is in paintings and even textiles, where the landscapes, though not perhaps an accurate depiction of an individual garden, reflect the prevailing style of the time.
The Met has a lovely online exhibit of gardens represented throughout art history; from a 1437 Ming Dynasty painted scroll to a 1944 Gorky painting.
One of the items is this late seventeenth century tapestry depicting a musical garden party and showing several features characteristic of gardens at this time:
the use of trellising and vining plants to create an outdoor 'room',
a formal arrangement of small beds divided by paths for strolling,
plants which were widely spaced to display each individual plant to best advantage.
At this time flowering plants were rare, limited varieties were available, and unusual ones were brought at great expense from long distance. Our modern, dense planting preference is a product of the happy abundance of plant material.
One of the most interesting things about this piece to me is that the people in it are actually depicted outside the garden, in the natural environment. In this time period, people considered the garden--formal, controlled--to be not artificial but 'truly' natural, a re-creation of what they imagined was the orderly state of the garden of Eden. More real than real, as it were. What we would call true nature was considered a dangerous and disorderly wilderness. So it is fascinating that in this work they and their instruments and their pets are outside the controll, safe confines of the garden.