New gardeners are taught that friable, loamy soil is great for their garden because it retains water but drains easily. While gardening does not require an advanced degree, some terms, such as "well-draining" soil and even "loam," can leave you scratching your head. Everyone knows that you need great soil to grow great plants, but what is this magical loamy soil so many gardening books say you should aim for?
What Is Loam Soil?
Loam soil is composed of almost equal amounts of sand and silt with a little less clay. A good ratio is 40 percent each of sand and silt, and 20 percent of clay.
Generally speaking, loam describes the ideal soil composition for most garden plants. (Some plants like sandy or rocky soil, and some even like clay.) Loam holds nutrients for feeding plants and has a texture that retains water long enough for plant roots to access it, yet it is well-draining, meaning that the water eventually flows away so the roots do not sit in water and rot. Without good soil, plants struggle to survive and usually require extra feeding and watering.
While it is possible for loam to be present naturally in an area that you choose to garden, it's more likely that the native soil will need some help to achieve the ideal composition. Improving garden soil is not a quick job, but it will pay you back with multiple benefits.
How Loam Soil's Components Work Together
Among loam's three components—sand, silt, and clay—the sand particles are the largest. Sand does not hold on to moisture, but it provides good aeration and drainage.
On the opposite end, clay particles are much smaller and easily compacted. That makes clay a great material for building bricks but not so great for allowing water, air, and plant roots through. However, clay tends to be higher in nutrients than the other soil components.
Silt is the medium-size particle, with better moisture retention than sand but fewer nutrients than clay. Silt helps clay and sand mix together more readily, like tempering chocolate.
In addition to providing nutrients and water effectively, loam has a loose and crumbly texture. This is referred to as friable. Loose soil provides room for air to mix into the soil, which is also necessary for optimal plant growth. The friable nature of loam also makes it easy for roots to grow and reach more nutrients and water.
How to Create Loam for Your Garden
Although loam is a combination of sand, silt, and clay, adding sand to your clay soil (or vice versa) will not create loam. Doing so will result in something like concrete.
Creating a loose, loamy, fertile soil is not a one-and-done garden task. Turning your existing soil into loam is an ongoing process that involves working organic matter into the soil every year. It is the decomposing organic material that creates the well-draining conditions plants need. Organic matter also attracts beneficial organisms that help keep the soil healthy and alive. Shredded leaves, straw, and finished compost work beautifully in creating rich, loamy soil as they decompose.
Unfortunately, organic matter is quickly depleted as it decomposes. This is why the must be amended each season. How much organic matter to add depends on how out of balance your soil is. If your soil is extremely sandy or predominantly heavy clay, it may need large amounts of organic matter added several times a season. However, for most soils, laying down at least a 2-inch layer of organic matter over the garden surface and then working it into the top few inches of soil should do it. Instead of bagging your fall leaves, add them to your garden beds to allow them to decompose and enrich the soil.
Can You Buy Loam Soil?
Buying soil in bulk can be a fast and easy way to get your garden or yard up and growing--but it can also be pricey. In addition, there is no standard or certification for soil quality, so you never know what you are getting. Many companies that sell soil are getting that soil from construction sites, where soil has had to be excavated for basements or to level a yard. Generally, soil from excavation does not make ideal garden soil. Use that type of soil, known as "fill dirt," for other yard projects but not for gardening.
If you intend to buy soil, compost, mulch, or other bulk garden material, know something about the company you are buying from. Don't be afraid to ask questions. Bringing in poor soil will not make your garden better and could actually set you back in your quest for great soil. However, there are many excellent soil companies that stand behind their products.