Understanding Your Soil: How Soil Conditions Affect Watering Needs

Soil Texture and Structure

While all soils are made up of the same four basic components, the particle size and interactions between particles play a significant role in the soil’s characteristics. These factors are referred to as texture and structure:

Texture:

Texture refers to the size distribution of soil particles and is categorized into sand, silt, and clay. Sandy particles are coarser (and themselves come in different sizes), clay particles are the finest, and silts are somewhere in between.

Soils generally contain a mix of all three sizes of particles, and how the soil acts is influenced by this ratio. Loam is the term used to describe soils that contain relatively equal amounts of sand, silt, and clay. Because loam has a balanced water retention and drainage capacity, it is often considered the ideal soil type for growing a wide variety of plants.

Structure:

Structure refers to how soil particles bind together to form aggregates and is influenced by factors like organic matter and moisture content.

Soil structure is broken into seven main shapes (platy, prismatic, columnar, blocky, granular, wedge, and lenticular) each of which influences how water moves through the soil, air infiltration, and response to freezing.

Common Soil Types and Their Watering Needs

Determining Your Soil Profile

There are two ways to go about determining the specific type of soil present in your yard. The first is to simply check a soil composition map. Soil composition can be relatively consistent across geographic regions. Here in Columbia, South Carolina we sit on the border of two regions and soils tend to be sandy loam, loamy sand, or sandy soils.
Alternatively, there is an easy DIY project known as the “Jar Method” which can provide surprisingly accurate results:

Soil types by clay, silt and sand composition as used by the United States Department of Agriculture
https://en.wikipedia.org/wiki/Loam#/media/File:SoilTexture_USDA.svg

Factors Affecting Soil Moisture Retention

Organic Matter Content

Organic matter plays a crucial role in enhancing a soil’s water retention capacity and aeration. It acts like a sponge, absorbing water and releasing it slowly over time, thus preventing rapid drying.

Additionally, organic matter introduces air pockets into the soil, facilitating better aeration. This allows roots to breathe and aids in the distribution of water throughout the soil.

Soil Compaction

Soil compaction severely restricts water infiltration and root growth. In compacted soils, the tightly packed particles leave little room for water to penetrate or for roots to expand. This leads to poor water absorption and can contribute to waterlogging in soils that naturally hold more moisture, such as clay soils.

Over time, compacted soil can become virtually impenetrable, preventing even surface water from being absorbed and causing runoff from the soil surface.

Soil Depth

The depth of the soil directly influences its ability to hold water. Shallow soils have less volume to retain moisture, making them more susceptible to rapid drying. On the flip side, deep soils offer a greater reservoir for water storage, providing a buffer against periods of drought or low rainfall.

In either case, understanding the depth of your soil can inform your watering strategies, ensuring that you neither overwater nor underwater your plants.

Improving Soil for Optimal Watering

Soil Amendments

Soil amendments are substances added to the soil to improve its physical and chemical properties, such as structure, water retention, and nutrient content. Examples include compost, well-rotted manure, and peat.

However, not all soils will benefit from the same types of amendments. Before making any amendments, it’s essential to understand your specific soil needs. Conducting a soil test can give you valuable insights into your soil’s pH levels, nutrient deficiencies, and other characteristics, helping you choose the most appropriate amendments.

Mulching

Mulching with organic materials like wood chips, pinestraw, or even grass clippings serves multiple purposes in soil management. Primarily, it reduces the rate of soil moisture evaporation, helping to maintain a consistent level of moisture for plant roots. As these organic materials decompose, they enrich the soil with nutrients and improve its structure. This, in turn, enhances the soil’s water retention capabilities.

Mulch also acts as a barrier against soil erosion and inhibits the growth of weeds, both of which can affect water distribution and root health. By integrating organic mulching into your soil management practices, you can effectively conserve water while enriching your soil.

Proper Tilling Techniques

Tilling is the practice of turning over the soil to break up compacted layers, improve aeration, and mix in organic matter. However, there is some debate over the usefulness of tilling, and in many cases tilling can actually cause more harm than good.

Tilling alters your soil’s structure and if performed incorrectly can lead to a phenomena called ‘hardpan’ where your soil develops a compacted layer just below the depth that was tilled. Plant roots will struggle to go deeper than this, limiting their rooting depth.

We recommend that unless you know what you’re doing, you avoid tilling for no reason. Sometimes it will be necessary to till soil to work in soil amendments – but otherwise this might be a chore to skip.

Tools and Techniques for Assessing Soil Moisture

All soils have a particular water holding capacity. The maximum amount is known as the field capacity – adding water beyond this point will only result in runoff. On the other hand, there is a point where soils are so dry that plants are no longer able to extract moisture. This is known as the wilting point.

To best take care of your lawn, it is important to keep your soil water content between these two levels. Watering your lawn when it is saturated is simply wasted water use, while waiting too long to water can induce water stress and cause plants in your lawn to suffer.

The Hand Test

The hand test is exactly what it sounds like: pick up a handful of soil and feel how moist it is. This is an inherently subjective test, and soil composition can impact soil feel. With experience, a gardener will be able to tell when soil is dry and needs to be watered.

Soil Moisture Meters

These are devices that can provide a numerical indication of soil moisture levels, helping you to water your plants more precisely.

Moisture meters come in both digital and analog versions, and both can deliver quick and accurate results.

Observing Plant Indicators

Plants often show signs like wilting or yellowing when they are either over-watered or under-watered. Hardier plants will do a good job of showing you when they need to be watered, while other plants may already be in trouble once they show signs of drought.

Grasses tend to be more robust, and once they lose their natural springiness and luster, they often will benefit from watering.