Question: Can I use soil dredged from Allatoona Lake in my vegetable garden?
Every winter, the Army Corps of Engineers must use a crane to dredge out silt and sediment from Allatoona Lake. If you drive by the Knox Bridge boat ramp on highway 20 near Canton, you will see the mountains of soil that they excavate from the riverbed where the Etowah River meets the lake. This dredging process is necessary to maintain a deep, healthy lake ecosystem. Otherwise with time, the lake would eventually fill up with silt that results from natural soil erosion, storm water, and sediment that runs into the Etowah River and ultimately ends up in the bottom of the lake.
The soil dredged from Allatoona Lake is made available to the public for “free”. All you have to do is bring a shovel, a strong back, and a pickup truck to haul it off from the pile on the side of highway 20. Have you ever heard the saying: “You get what you pay for?” Sometimes, “free” soil is not the most economical choice for you garden and you may end up with more problems that end up costing you time, labor, and money in the long run.
We frequently receive questions about the use of soil amendments such as the soil dredged from Allatoona Lake. We’ve gotten this question so often that I had to pull a soil sample for testing, just to prove a point. When the results came back from the lab, I wasn’t surprised to find that the pH was low (acidic) and the content of essential plant nutrients was very low. In other words, you’re not getting any free nutrients or fertilizer value from this dredged material. In fact, you will need to add lime and fertilizer if you plan to use this in a garden and grow successfully. You will want to do an additional soil test for your garden after you incorporate this type of soil to see exactly what your garden is lacking.
I would also caution the use of too much of this silty-loam sediment in a clay-based soil. When combining the two, it can bind with the clay and create a highly compacted soil with poor drainage. The addition of sand or silt to a clay soil actually defeats the purpose of amending the soil. The primary purpose of adding any soil amendment to your garden is to loosen the soil, minimize soil compaction, and improve drainage. If your soil is already poorly drained (like most clay soils), then you probably should not use any of the dredged soil from Allatoona Lake in your garden.
The best soil amendment for clay is traditional compost from a local garden center or farm supply store that contains organic matter such as peat moss or composted pine bark fines. You can add about three to four inches of compost material over a garden and thoroughly mix or till-in to a depth of eight to twelve inches. Since compost and organic matter quickly breaks down in our climate, these soil amendments are usually added once a year to vegetable gardens and annual flower beds. Because organic matter quickly degrades, there are no long term benefits to adding soil amendments to perennial plants such as trees and shrubs that live longer than a year.
It’s important to thoroughly mix any soil amendments with your underlying clay, since many of the micronutrients needed for plant growth are actually in the clay soil. Many clients make the mistake of building a raised bed garden without incorporating the underlying clay soil with their soil amendments and end up with nutrient-deficient plants.
About the only good use for this “free” soil from Allatoon Lake is to fill a hole in your yard or driveway. In summary, dredged soil from Allatoona Lake probably isn’t the best soil to use as an amendment for vegetable gardens. First, it tends to drain poorly due to the silt content which may cause root-rot and disease problems in your garden. Second, it contains almost no nutrient value. And third, it may contain a random assortment of weed seeds, which may create more work in the long run. You would be better off buying the cheapest bagged soil amendments/conditioners from a local garden center which are clean and free of weed seeds. These soil conditioners have a more loose mixture of composted bark fines and organic material that drain better and help loosen your clay soil. No matter what soil amendment you use, be sure to incorporate uniformly with the existing clay to improve drainage and nutrient holding capacity of your soil.
Paul Pugliese is the Extension Coordinator and Agricultural & Natural Resources Agent for Bartow County Extension, a partnership of The University of Georgia, The U.S. Department of Agriculture, and Bartow County. (770) 387-5142. For more information and free farm, lawn, or garden publications, visit our local website at ugaextension.com/bartow .