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The experimental biochar terrace garden

Considerable labor was required to build terraces on the sides of Georgia's mountains.
Considerable labor was required to build terraces on the sides of Georgia's mountains.
© Richard L Thornton, Architect

Why, over a thousand years ago, did the inhabitants of North Georgia build massive complexes of agricultural terraces, when at the same time they were farming rich river bottom lands nearby? The answers are being found at an experimental terrace garden near Amicalola Falls and the beginning of the Appalachian Trail in the Georgia Mountains.

A unique Native American culture existed in the Southern Highlands and Piedmont in the period between approximately 800 AD and 1700 AD. It contained two provinces, Itsapa in the highest mountains of Georgia, plus Apalache in the lower mountains and Upper Piedmont. For many centuries, Itsapa was dominant, but after around 1585, Apalache created a confederacy that spanned most of the Southern Highlands and Piedmont. The archaeological term of “Lamar Culture” corresponds to this confederacy. The Appalachian Mountains are named after the Georgia Apalache. The Florida Apalachee began as a colony of the Georgia Apalache. Tallahassee is the Anglicization of the Apalache words Tula halwasi, which mean “Town from the Highlands.”

Although at the time that the History Channel crew filmed the premier of “American Unearthed” in July 2012, the Track Rock Terrace Complex was thought to be unique, People of One Fire researchers have now identified at least a dozen agricultural terrace complexes in northern Georgia and smaller terrace gardens in northeast Alabama and northwest South Carolina. Logs were a far more common structure for retaining walls than stone. Apparently, stone was only used when trees were no longer in easy hauling distance.

The large terrace complexes are located in a relatively narrow corridor that has a northern apex at Track Rock Gap, GA and extends southward to Metropolitan Atlanta. The largest terrace sites can be found overlooking river gorges in Union, White, Lumpkin, Dawson, Pickens, Forsyth, Banks, Jackson, Barrow and Gwinnett Counties Surprisingly, the largest and apparently oldest concentration of terrace complexes are in Metro Atlanta along the Apalachee, Mulberry, Middle Oconee and North Oconee Rivers. The Apalache Foundation was incorporated in June of 2014 to obtain funding in order to hire qualified archaeologists, geologists, botanists, architects and civil engineers to study these many stone ruins.

The terraced town sites in Metro Atlanta adjoin tributaries of the Oconee River that rush down the Blue Ridge Foothills through gorges. All of the sites overlook “white water” shoals, a few, waterfalls. Some of the locations show evidence of being Woodland Period ceremonial sites prior to becoming more heavily populated. It appears that stone cairn cemeteries were located on the southwest slopes of hills or mountains, long before terraces were built. The surviving stone architecture zones were skipped over by real estate developers because of the rugged terrain or else being in flood hazard areas.

Biochar agriculture

Biochar agricultural is a technology for soil fertility improvement that was apparently developed in the Amazon Headwaters region then spread into Central America. The initial step is the construction of terraces or raised beds with fill soil. Broken pottery (potsherds) or small shale stones, along with charcoal, are mixed with the fill soil. Throughout the use of the biochar soil, wood ashes, organic kitchen refuse and human urine are added to the soil.

After friendly bacteria in the special fill soil get to growing, the soil becomes extremely fertile locations for a wide variety of vegetables and fruits. Botanists and archaeologists, who studied the biochar farming locations in Amazonia determined that they were capable of supporting very dense populations.

In 2001, an archaeological firm in Stone Mountain, GA was retained to analyze soil samples from a terrace at Track Rock Gap. The firm’s lab obtained a radiocarbon date of c. 1018 AD for the bottom of the fill dirt. It also noted large quantities of charcoal and potsherds mixed with the soil. Perhaps because it never dawned on these archaeologists that Mesoamericans or South Americans might have settled in the Georgia Mountains, the lab did not get the connection between the potsherds and charcoal with biochar agriculture.

The Track Rock terrace complex is an enigma. Although this fact was not mentioned in the USFS sponsored archaeological report, the terraces were literally in walking distance from conventional proto-Creek towns with mounds that shared cultural traits with Etowah Mounds. The conventional towns obviously practiced river flood plain agriculture. Why did the builders of Track Rock feel compelled to expend so much human energy to farm on the steep slopes of a mountain?

Description of experimental garden

The experimental garden is located in almost identical soil chemistry and solar orientation as found at Track Rock Terrace Complex. The dark woodland loam contains some soapstone (steatite) and white quartz rocks. The quartz contains gold. There are the ruins of two gold mines within a few hundred yards of the garden. The experimental terraces were constructed in an arc that faces the azimuth of the Winter Solstice sunset (southwest.)

The climate of the experimental garden is slightly warmer than Track Rock Gap during the growing season. The garden’s location runs about 10-15 degrees F. cooler than Atlanta and about 0-4 degrees F. warmer than at Track Rock Gap in mid-summer. Summertime low temperatures at night in rural sections of the Georgia Mountains often dip as much as 20 degrees F. below Atlanta. The location averages about 66 inches of precipitation a year, which is 10 inches more than Track Rock Gap.

Storm water running off the hill above the garden is channelized at the top of the garden then runs in a zigzag pattern down through the terraces. At two locations much deeper ditches were dug to retain water for longer periods.

The garden is currently about 150 feet north-south and 60 feet east-west. The original garden, seen on the History Channel was about half that size. Work was begun on the garden on May 1, 2012 after a Bobcat mini-bulldozer cleared off the saplings and undergrowth. The larger trees were sawed down and used for retaining walls. It is highly probable that most of the terraces at Track Rock Gap were originally log-walled. Stones were only used extensively after all the nearby trees were gone. The terraces were created with a pick, shovel, hand saw and small cart for hauling dirt. The logs are held in place by wooden pegs.

Cultivation of the experimental garden generally followed Native American farming practices, except the use of metal tools. No chemical fertilizers or insecticides are used in the experimental. All cultivation is done with metal hand tools. After the first season, the soil became so fertile and soft that tillers or tractors would have been unnecessary anyway. Relatively heavy amounts of wood ashes and organic kitchen refuse have been worked in the soil over the past two years. Some diluted, human urine has been used on crops that are particularly demanding of nitrogen and potassium. After the first and second seasons, the garden terraces were burned over to help reduce fungus and nematode populations.

Amazing results after the first year

Tomatoes thrived in the first season of the garden. The first year garden looked spectacular when filmed by the History Channel in early July. The region was experiencing exceptionally high temperatures and a drought. Several members of the film crew remarked that my garden was the only green garden they had seen, driving to the site. The terraces and rainwater storage system definitely made the difference between a dead garden in a drought and a productive garden.

Soon thereafter, fungi in the woods soil quickly killed all the members of the squash-pumpkin family. The corn cobs were very small. Members of the bean family produced about the same amount of food as conventional garden. Insects did a lot of damage to the plants in August. There were few predators to reduce their population.

I planted members of the cabbage family in late September of the first season. All members of the cabbage did exceedingly well. Many of the varieties stayed alive throughout the winter and could be utilized on the dinner table. It was a mild winter, however. The next winter had several nights that dipped below O F. This would have killed all plants.

Between the first and second season, I was able to make significant improvements in the soil fertility by continuing to add ashes and organic refuse. The ashes reduced acidity, plus killed fungi spores and nematodes that are inherent in woodland soils. The corn plants didn’t even produce edible ears.

During the second season all crops except corn had productivity significantly above nearby conventional flat gardens that relied on chemicals. Again as in the first year, the squash varieties produced a bounty of produce then suddenly died from fungal infections during the second week of July.

The third season of the experimental biochar garden has been remarkable. I planted seven varieties of indigenous American beans plus green beans, which are from Europe. All of these legumes have tripled the quantify of food produced, when compared to last year. Many of the bean plants are 11-12 feet high. Squash plants did not suddenly die of fungal infections in early July, but by early August, stopped producing large fruits. The corn plants produced edible ears, but they are smaller than in conventional gardens. A big change this season is that the non-chemical environment has attracted a wide range of predators that eat plant-destroying insects. I did have to resort to spraying “aphid farms,” established by dairy ants in July, with soapy water. The detergent kills the aphids and ants, but is non-toxic to the plants and humans.


There seems to have been several motivations for building the mountainside terraces. The terraces shade the bases of the plants and therefore reduce water evaporation. It is possible to irrigate plants on terraces with gravity fed water, stored during rainstorms. The indigenous peoples of the region would obviously not have had electric water pumps. During the 2012 drought, the experimental terrace garden continued to thrive while conventional gardens died. Constructing the terraces in the Georgia Highlands could well have been a “life insurance” practice during a climatic period when droughts were frequent. Today, though, droughts are a rare occurrence in that region. They do happen some years.

Potatoes, tomatoes and members of the bean family grow like kudzu in an environment that mimics the Track Rock terraces. Members of the squash-pumpkin family will grow there, but not quite as well as in stream bottomlands. Corn does not grow well in the location that mimics Track Rock Gap. The local county agricultural extension office suggested that the reduced level of sunshine in that situation inhibited the ability of the plants to produce ears. So the “best guess” is that Track Rock Gap’s terraces were covered in many varieties of beans, with other types of vegetables being grown there in case a drought wiped out production in the nearby river bottomlands.

Biochar agriculture is not a quick fix. It has taken two years to see a radical change in the soil chemistry of the experimental garden. However, it does work. This relatively small garden on the side of a mountain is capable of producing most of the vegetables for a family.

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