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?
Loam Soil Components
Loam soil, the ideal growing medium for the vast majority of garden plants, includes three components:
- Sand, comprising about 40 percent of the soil total by volume.
- Silt, comprising roughly 40 percent of the soil total, by volume.
- Clay, comprising the remaining 20 percent of the soil total.
While it is possible for loam to be present naturally in a garden bed, it's more likely that the native soil will need some help to achieve the ideal composition. Improving garden soil is not a quick and easy task, but the results are well worth it.
Generally speaking, loam describes the ideal soil composition for most garden plants (although some plants require sandy or rocky soil, and some even require clay). Loam holds nutrients and has a texture that retains water long enough for plant roots to access it, yet it drains well— meaning that the water eventually seeps away so that plant roots do not sit in water and rot. Without quality soil, plants struggle to survive and usually require supplemental feeding and watering.
How Sand, Clay, and Silt Work Together
Among loam's three components—sand, silt, and clay—the sand particles are the largest. Sand does not hold moisture, but it lends good aeration and drainage as a component of loamy soil.
On the opposite end, clay particles are much smaller and are 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, somewhat like tempering chocolate.
In addition to providing nutrients and water effectively, loam has a loose and crumbly texture. This is referred to as being friable. Loose soil provides room for oxygen to be present in the soil, which is also necessary for root growth. The friable nature of loam also makes it easy for roots to spread out to consume nutrients and water.
How to Create Loam for Your Garden
Although loam is a combination of sand, silt, and clay, adding sand to clay soil (or vice versa) will not create loam. Doing so will result in a material similar to concrete. Rather than trying to immediately create the correct proportions of sand, silt, and clay, improving soil is best done by adding plenty of organic matter. This nurtures soil organisms that over time transform the soil into a loamy mixture.
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 incorporating organic matter into the soil every year. The decomposing organic material creates the well-draining conditions plants need. Organic matter also attracts beneficial organisms that keep the soil healthy and alive. Shredded leaves, straw, and finished compost work beautifully to create rich, loamy soil as they decompose.
Unfortunately, organic matter is quickly depleted as it decomposes. This is why you must amend the soil each season, preferably in the fall. How much organic matter to add depends on the balance of the soil. If your soil is extremely sandy or predominantly heavy clay, it might need large amounts of organic matter added several times a season. However, for most soils, laying down 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 fallen leaves in autumn, shred them and add them to your garden beds where they will 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, while there are certifications programs offered to help consumers, retailers, regulators, and others identify high quality soil, they are voluntary at this time. Many companies that sell soil are obtaining that soil from construction sites where soil has been excavated for basements or to level a yard. Generally, soil from excavation sites does not make ideal garden soil. Use that type of soil, known as "fill dirt," for other yard projects, but not for growing plants.
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. Trusted and well-known soil companies stand behind their products.