First, let's talk garden layout. From the 17th century to the 19th, not a lot changed in typical gardens. They were square or rectangle, often with raised beds, and small (compact may be a better description). They were enclosed with small fences, typically made from green branches interwoven and staked at about knee high, just enough to keep rabbits and smaller critters out. There were also sometimes "living fences" of small shrubs. G. Washingston even spoke of the effectiveness of Honey Locust when used as a fence line at his estate. The walkways were paved with crushed shells or gravel, or just a dirt path of they had no option. Space was optimalized and herbs were typically placed alongside vegetables, excepting the most pungent which were isolated. Later fruit trees would be integrated, usually around the perimeter or in the center of a raised bed that was otherwise used for ground crops.

If you had a little money, things were better. Terrace farming was utilized and crops like lettuce would be placed on hills in relation to the sun in order to increase the growing season by capitalizing on the warmer soil provided. Odd specimens could gain space. Long rows of beans or peas could be planted in dedicated plots.

What did you grow? Indian Corn/Maize, squash, onions, radishes, beans, peas, pumpkins, cabbage, carrots, lettuce are all very common plants in colonial gardens of the mid Atlantic at that time. Every garden would have most or all of those by the 19th century (or at least could have them, many did). There were about 200 different plants found in various Williamsburg gardens in the late 18th century, according to Colonial Williamsburg historians. Certainly some of these were not common in typical gardens, but many of them were. Jefferson, who had an atypical garden, listed his herbs one year as:

Sage (Salvia officinalis), Balm (Melissa officinalis known as lemon balm), Mint (Mentha piperita), Thyme (Thymus vulgaris), Lavender (Lavandula angustifolia), Marjoram (Majorana hortensis), Camomile (chamomile - Anthemis nobilis), Tansey (tansy - Tanacetum vulgare), Rue (Ruta graveolens), Wormwood (Artemisia absinthium), Southernwood (Artemisia abrotanum), Rosemary (Rosmarinus officinalis), Hyssop (Hyssopus officinalis), Perywinkle (periwinkle - Vinca minor), Marshmellow (marshmallow - Althaea officinalis), and Beargrass (Yucca filamentosa).

They tended the soil with fish, manure, and animal parts. One source suggested planting certain crops in a hogs head for nutrients.

Who was John Bartram and how can Mr. PantsnJaket, as he often does, connect this to Dr. Franklin? John Bartram was a very important early botanist. He was actually the first one (sort of, my great uncle had already written New England Rarities years before Bartram was born) and in 1728 he purchased land in Pennsylvania, then established America's first botanical garden on it (It still exists today, almost 300 years later, as Bartram's Garden in Philidelphia). He would be appointed by George III as the Royal Botanist for North America in 1765, permitting him to travel throughout the colonies and discover flaura and fauna found within. He sent many specimens back to Philidelphia, where they were cultivated at his gardens. In the 1740s he had joined with some other gentlemen and formed the American Philosophical Society - among them was, of course, his good friend and fellow Philidelphian, Benjamin Franklin.

Bartram traveled south with his son, William, and explored the Carolina's and Georgia. They found a curious plant near the Altamaha River in Georgia, a vibrant ecosystem with diverse biology and wildlife. They returned to Philly, but in 1773 William would again travel south for natural discovery and detail his journey in Travels through North and South Carolina, Georgia, and Florida. In reality he went all the way to current day Louisiana, but the lands of modern Alabama and Mississippi didn't really have a colonial name in 1773. In fact most of Georgia still didn't have settlements and Atlanta wouldn't even exist as a tiny train terminus for another 60 years. William decribes the Altamaha watershed in 1773;

...It has its source in the Cherokee mountains, near the head of the Tugilo, the great west branch of the Savanna, and, before it leaves them, is joined and augmented by innumerable rivulets; thence it descends through the hilly country, with all its collateral branches, and winds rapidly amongst the hills two hundred and fifty miles, and then enters the flat plain country, by the name Oakmulge (Ocmulgee); thence meandering an hundred and fifty miles, it is joined on the east side by the Ocone (Oconee), which likewise heads in the lower ridges of the mountains. After this confluence, having now gained a vast acquisition of waters, it assumes the name Alatamaha (Altamaha), which it becomes a large majestic river, flowing with gentle windings through a vast plain forest, near an hundred miles, and enters the Atlantic by several mouths.

They found a "curious shrub" bearing "fruite" but paid it little more than mention on the first trip. They had thought it similar to Gordonia lasianthus (Loblolly Bay, an evergreen shrub) and he had refered to it as Gordonia pubescens due to the hairy appearance it has. William had found it again, in the same spot, and took a sample. He wrote:

(W)e never saw it grow in any other place, nor have I ever seen it growing wild in all my travels

He couldn't find it elsewhere. He then discovered from the botanist Dr. Daniel Solander that it was not actually Gordonia at all, but a different species all together. Nobody ever found another specimen of the curious plant except in a roughly two-acre area directly adjacent to the beautiful Altamaha. The last confirmed sighting of wild growth would come in 1790 on a collection expedition, and it was found in the same small plot outside Fort Barrington, GA. He named it Franklinia Altamaha for his, and moreso his father's, close personal friend and for the beautiful river on which he found it. It is a member of the Theaceae family for you botanists. The only place it existed at the turn of the 19th century, and even today, is gardens.

Now that Dr Franklin is out of the way, any other noteworthy add ons about mid to late 18th century gardens? Of course, Mr. Thomas Jefferson and his grand gardens of Monticello. Monticello has a garden terrace about as long as three American football fields - that's 1000' (or slmething-something meters), and held over 330 different plant varieties, more than 70 species. He had plants from the Lewis and Clark expedition (not quite in the 18th century, of course), peppers from Mexico, 20 varieties of beans and 30 of peas. He had cherry trees lining the drive. His network of seed exchange and his experimentation in gardening was one of his greatest contributions. Today we may still enjoy the fruits of his labors, as Thomas Jefferson's Monticello sells seeds raised from the decended plants Jefferson himself procured seeds for and noted every detail of, allowing you to create your own unique yet accurate fancy colonial garden.

About the soil, Jefferson said;

We will try this winter to cover our garden with a heavy coating of manure. When earth is rich it bids defiance to droughts, yields in abundance, and of the best quality. I suspect that the insects which have harassed you have been encouraged by the feebleness of your plants; and that has been produced by the lean state of the soil. We will attack them another year with joint efforts.

New England's Rarities Discovered, John Josselyn, 1663 - full book: https://books.google.com/books/about/New_Englands_Rarities_Discovered.html?id=iWSC6HwiixsC&printsec=frontcover&source=kp_read_button

Travels through North and South Carolina, Georgia, and Florida, William Bartram, 1791 - full book: https://books.google.com/books/about/Travels_Through_North_South_Carolina_Geo.html?id=WrJgAAAAcAAJ&printsec=frontcover&source=kp_read_button

Jefferson's Garden Book is 700 pages of late 18th/early 19th century gardening delight in specific detail from Jefferson himself! Unfortunately it has been reprinted numerous times and must be purchased. It can be browsed curtousy of the Massachusetts Historical Society here - https://www.masshist.org/thomasjeffersonpapers/garden/

And if you must start your very own colonial garden, start with Vegetable Gardening the Colonial Williamsburg Way by Wesley Greene.