Know the Types of Soil

Every gardener wants to grow the best-tasting tomatoes, the brightest zinnias, and the healthiest shrubs, but no one type of soil will guarantee success for each of those plants. Soil type is a classification determined by texture and relative proportions of the three main types of soil particles: sand, silt, and clay. “This really means the size of the particles that make up your soil and give it its texture,” says Juliet Sargeant, a garden designer in West Sussex, England, and author of Start with Soil.

Although you’ll find other names for soil types to describe chalkiness or pH, it’s best to first understand those three basic particles:

• Sand: Gritty sand lets plenty of water drain through, and sandy soil often lacks moisture and nutrients many vegetables and flowering plants need, but supports drought-tolerant plants.
• Silt: More fertile than sandy soil, silt particles’ size is between large sand and small clay; these soils often are fine and soft.
• Clay: Clay soil particles are so tiny that they pack tightly together and become heavy enough to block oxygen. It’s sticky when wet but can turn bone dry and crack in summer.

Soil with a nearly equal balance of these particles is called loam. Read on for more facts about the four types of soil and how they affect your plant choices, plant health, and soil maintenance.

Types of Soil

According to Sargeant, the type of soil that makes up your lawn and gardens might not be ideal, but it certainly is unique. “Each geographical area has its own bedrock, which creates a unique soil structure,” she says. Each patch of ground also lives through specific climatic and biological conditions unique to the area that leads to different types of soil. “The soil in your garden is like no other on Earth; it’s uniquely yours to look after,” says Sargeant.

While looking at the characteristics of soil types below and how to easily determine the type in your garden, focus more on how to work with the unique soil you have and less about trying to make it ideal. Read your favorite plants’ soil descriptions to learn what kind of soil drainage and qualities they need. Attempting to change the soil completely is likely a losing battle, although you can take steps to support moisture retention or add nutrients. Try not to stress about achieving the perfect soil, though. “You are literally fighting against nature,” says Sargeant.

Sandy Soil

Made of up ground rock particles, sandy soil has the largest particles of the three main types. It can lack nutrients and moisture, since water drains quickly through. Sandy soil usually dries out between watering. Depending on the type of rock particles and other matter your soil contains, its pH level could be in the acidic or slightly alkaline range. 

Characteristics: Large particles and a gritty feel; soil drains and dries out quickly.

Pros and cons: Provides good air flow to roots, but does not hold moisture or vital nutrients well. 

Best for: Drought-tolerant plants like California poppies, crape myrtle, butterfly milkweed, gazania, yarrow, lavender, rosemary, and cosmos all do well in sandy soil with regular watering.

Working with sandy soil: Apply water slowly (drip) to slow the flow of water straight through the soil. Mix in organic matter such as compost every spring and fall to help suck up and retain moisture. Fertilizers also drain through, but you can apply light balanced organic fertilizers once a month during the growing season. Add mulch above the soil to help retain moisture around plants.

Silty Soil

If you live in an area that was once a riverbed, chances are good that you have silty soil, which results from eroded rock particles transported by water, ice, or wind. More fertile than sandy soil, silt particles are fine and soft. Silt’s pH level can vary from slightly acidic to slightly alkaline. With just a little amending to improve drainage, silty soil is excellent for vegetable gardening.

Characteristics: Particles are between sand and clay size and will not clump easily when squeezed. Also drains well, but can compact.

Pros and cons: Silt usually is nutritious, as it holds water and nutrients better than sandy or clay soils. However, it also is delicate and tends to compact, which can reduce drainage and restrict oxygen from reaching plant roots. 

Best for: Lush vines, flowers, vegetables, and moisture-loving plants that tolerate damp roots, including all types of willow trees, dogwood trees, many iris varieties, peonies, roses, and vines such as ivies and Virginia creeper.

Working with silty soil: To reduce compaction problems, add soil amendments. Work a few inches of compost or composted manure into the top 6 inches of soil before planting in the spring. Apply additional compost around plants during the growing season, and spread a layer of dried leaves or other mulch over the soil bed in late fall, leaving it to overwinter.

Clay Soil

Clay soil particles are miniscule and pack tightly together, locking in moisture and nutrients, but restricting oxygen and drainage. Clay soil tends to be slightly alkaline in pH. Woody perennials, such as wisteria, tend to do well in non-amended clay soil. Because clay is high in nutrients, with frequent amending to increase drainage and airflow, you can expand its growing ability to accommodate a variety of vegetables, shrubs, and flowering plants.

Characteristics: At least one-quarter of its makeup is tiny clay particles. If you roll it between your fingers, it maintains a cylindrical shape.  

Pros and cons: Clay is slow to drain water, so it holds moisture and nutrients and makes nutrients available to roots. However,  it is heavy and difficult to dig and can compact easily, even from frequent foot traffic.

Best for: Woody, moisture-loving perennials like hostas, irises, sedges, and astilbe in most clay (especially wetter soil); sedum, echinacea, phlox, and rudbeckia in hotter and drier climates.

Working with clay soil: Till clay soil only when it’s bone dry to prevent creating rock-hard clods. Amend clay soil by adding a thick, 3- to 4-inch layer of mulch like dry leaves or bagged wood chips in the fall, waiting until spring to till it under. Work additional organic matter into the soil in spring before planting to reduce compaction and promote drainage.

Loamy Soil

If there’s any near-perfect soil type, it’s loam, which is a fairly balanced blend of clay, sand, and silt. Loamy soil drains well and is high in nutrients. The pH level varies, but tends toward more neutral or slightly acidic than other soil types. 

Characteristics: Moist loam squeezed in your hand will hold its shape, but crumble if poked lightly. Loam generally is darker in color than other soil types and has an earthy smell. 

Pros and cons: There are no real drawbacks to loamy soil, though some can lean toward more silt or clay in their makeup and might need regular attention to maintain their nutrient-rich qualities.

Best for: Flowers, vegetables, and virtually any type of plant, with some additives to grow plants that prefer more alkaline or acidic soil.

Working with loamy soil: A light application of compost or a 1-inch thick layer of dry leaves or mulch is usually all that’s needed to keep loamy soil healthy. Spread the organic matter on top in the fall and allow it to naturally decompose over the winter, then turn it under in spring before planting.

Other Soil Types

Aside from the three major types of soil particles and the ideal balance in loam soil, you might see reference to other soil types or textures. That’s because soil differs so much based on the percentage of each particle. For example, silt loam soil is 25 percent sand, 10 percent clay, and 65 percent silt. Other subtypes include sandy clay, clay loam, and sandy loam, but there are up to 12 combinations.

In addition, you might see reference to other characteristics of soil, such as whether it’s alkaline or acidic, which refers to the soil pH more than the texture. Some soils also include high amounts of minerals or organic materials such as peat, and all of the characteristics overlap (for example, chalky or lime soil contains lots of calcium carbonate and is typically alkaline in pH). It can veer toward light like sand or heavy like clay. Peaty soil really occurs only in bogs and wetlands and is high in organic matter and spongy to the touch.

“The makeup of soil is tremendously complex,” says Sargeant.”Scientists are only just starting to understand how it works.” In all likelihood, you are not alone with whatever soil type and characteristics you find on your property, so talk with local master gardeners or extension agents if you are having trouble finding the right plants or how to work with the soil you have instead of buying lots of amendments and garden soil. 

Understanding Soil pH

Your soil’s pH value is a measurement of its acid-forming capacity and can vary even within some soil types. The pH scale ranges from 1.0 to 14.0. 

• Below 7.0 indicates soil in the acidic range; the lower the number, the greater the soil’s acid-forming ability. 
• Higher than 7.0 is the alkaline range; the higher the number, the greater the soil’s alkalinity. 
• Slightly acidic soil pH (6.0 to 7.0), often loam, is considered optimal for most plants and flowers.
• Try amending soils that are too acidic by applying products that contain lime or wood ash.
• Reduce alkalinity with a product that contains aluminum sulfate, urea, or elemental sulfur.

How to Tell What Type of Soil You Have

You can assess your soil to at least guess whether it is silt, clay, sand, or loam. Begin by looking at the soil, feeling it, and squeezing a moist handful to see which soil type it most resembles. Note clues of soil type and health such as:

• Healthy and loamy soil in your hand crumbles into a variety of sizes, while clay stays clumped and sand fails to hold together.
• Note how that same sample feels. Clay might feel sticky, while sand is gritty and silt is soft and slippery like soap. 
• Loamy soil and other types with good amounts of organic matter appear darker; pale gray soil is a concern.
• Smell the soil to see if it has an earthy, fresh scent, which is a sign of healthy soil.
• Dig down and across about 4 inches of soil to look for earthworms, another sign of healthy soil.
• Observe which plants thrive in your current lawn or in natural areas closest to your property; the soil probably matches their favored soil (like sand or clay). 

Easy DIY Soil Type Test

After observing your soil, you can take it a step further by doing a simple jar test.  Continue to observe the soil as you gather your sample, looking for plant or mineral material and observing the color and texture.

1. Grab a clean empty (clear) jar with a tight-fitting lid.
2. Take a hand trowel and dig up a small amount of soil to fill less than a third of the jar. 
3. Add the soil through a mesh sleeve or old kitchen strainer if necessary to filter out large rocks and organic matter.
4. Add clean (even better, distilled) water until it reaches just over an inch from the top of the jar.
5. Close the lid and shake the jar vigorously until the contents look like slurry.
6. Set the jar on a level surface until the particles settle (at least a minute).
7. Using a marker or tape, make a line at the top of the coarse bottom layer.
8. Let the jar sit for 2 more hours and mark the next settled layer, which is the silt portion.
9. Leave the jar in place for 2 more days; the clay layer settles on top of the silt.
10. Measure the height of each layer and the total height of the sample/water mix in the jar. 
11. Calculate the percentage of each layer and then refer to the soil triangle or this helpful list to determine whether your soil is mostly sand, silt, clay, or some combination.

Home or Professional Soil Testing

A more complete soil test kit or soil sample sent to a laboratory can give you additional information about your soil’s pH and nutrients. Commercial home soil test kits can help you identify your soil’s pH value, which might be especially important if you have a soil variety that appears to be other than loam or if you want to grow a vegetable or ornamental that needs the right pH to survive. Home kits also can tell you which nutrients are present or lacking in your soil. The precise nutrients tested vary by kit, so be sure to read the information carefully.

For a minimal fee, you can find out your soil type (subtypes), its pH level, and how to improve garden soil. Check with your local county extension office for information on their recommended labs, pricing, and soil collection instructions. The basic test should be plenty for most home gardeners.

 

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