Robyn Stewart
I’ve been getting a lot of questions lately around soils for raised beds and home gardens. Unfortunately, most of these calls are coming 2-3 months after seeds have been planted, when nothing is growing and it’s clear there is an issue. While there are many reasons that plants won’t grow or thrive, poor soil or growing medium choice and failure to make amendments are the first things I look at.
Soil is the medium that serves to anchor plant roots, allow root growth, and store nutrients. It is composed of minerals, air, water, organic matter, and microorganisms. Texture is determined by the ratio of sand, silt, and clay particles in a given soil. Lincoln County has a huge variety of soil textures but two of the most prominent are silt loam and clay loam. When planning to garden, it is essential that we have a soil that can: hold nutrients, drain excess water, and allow for root and plant growth.
Whether you are creating a mixture of materials or planting in native Lincoln County soil, it is essential that you know the nutrition status of your soil before you even consider planting anything. In our region, we typically have to make soil amendments for both pH and nutrition. This is the process of adding lime and fertilizer to your soil to ensure that the right conditions for plant growth are met. If you add lime without fertilizing, you have simply changed the pH and have not added essential nutrients for plants (typically we need to add Nitrogen, Phosphorous, and Potassium). If you fertilize without checking and altering the soil pH, the plants may not be able to uptake the nutrients added by the fertilizer. Adding both lime and fertilizer according to a soil test is the first step in ensuring the growth and health of your plants.
When considering your garden, there are several different types of growing media or soil amendments to consider. You can use the existing soil in your garden or raised beds, but be sure to check how compacted it is, how well it drains, and make the correct amendments according to your soil test. We typically recommend using no more than 20% topsoil in raised beds and container gardening as it can have nutrition and drainage issues. A second option are commercial soilless mixes, which are specifically designed for container and raised bed gardens. They are lightweight and hold nutrients while maintaining good drainage, while also being free of weeds, insects, and other pathogens that could impact your garden. Most soilless mixes use a combination of peat moss, perlite, vermiculite, composted bark, compost, lime, and fertilizer. Some gardening methods (such as Square Gardens) recommend making your own soilless mix using peat moss, vermiculite, and compost- I would highly recommend you soil test that mixture if you choose to make it yourself. I have seen issues with excess and deficient nutrients in gardens planted with homemade soilless mixes this year. Other commercial mixes may be advertised as potting soil, planting soil, topsoil, and more. These products vary greatly in composition and quality, so be sure to look for a light, uniform mixture. Another common addition to soils is compost, which is a dark, crumbly product made when organic matter like leaves, grass clippings, and manure are decomposed. Compost is a good addition to any garden because it contains all of the major and minor nutrients that plants need for growth. The nutrients from compost are usually slow to release and your garden will require additional fertilization throughout the growing season. You should also keep in mind that not all compost is created equally; properly made compost should have reached temperatures that kill weed seeds and pathogens. The use of fresh manure on gardens can provide excess nutrients (especially Nitrogen) and cause plant disease and death, so composting first is the better option. Some suggested growing mixtures can be 100% compost, 100% soilless mix, and 50% soilless mix + 50% compost (you may use topsoil in any of these mixes at no more than 20% of the mix).
Getting the proper soil and planting medium for your garden can be a great insurance policy for the health and growth of your plants. Typically, soil quality and test results are one of the first things I ask about when someone has a gardening question. If you have any questions about developing an appropriate gardening mix, please reach out to us at uge3181@uga.edu and 706-359-3233.
