Everything You Need to Know About Garden Soil Types

Reader Contribution by Michael Feldmann
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Photo by Michael Feldmann

Soil is much more than simple dirt. On close inspection, garden soil is a complex mixture of mineral particles, organic materials, moisture, living organisms and chemical nutrients. Different soil types contain different amounts of minerals and nutrients, providing different levels of plant life improvement. The quality of crops depends on the top soil, the nutritional value in which they grow.

In order for the crop harvested from the fields to be rich and healthy, a farmer would do well to know the basic properties of the soil, its types and preparation rules before planting plants. There are over 20,000 soil varieties worldwide. But the most common and important types of soils are six main groups of soils: clay, sandy, silty, peaty, chalky and loamy. Each of them has its own good properties, and it is important to know them in order to make the best choice and get the most for your garden.

The 12 Scientific Soil Orders

Science classifies soils into 12 orders of magnitude depending on the region in which they occur, the plants that grow in them, and the climatic variables that affect them.

  • Alfisols is a highly fertile and productive agricultural soil in which clays commonly accumulate below the surface. Found in humid and subhumid climates.
  • Andisols. Often formed in volcanic materials, these highly productive soils possess very high water- and nutrient-holding capabilities. Usually found in cool areas with moderate to high levels of precipitation.
  • Aridisols are formed in very dry (arid) climates. Lack of moisture limits weathering and leaching, which leads to both salt accumulation and limited subsurface development. Commonly found in deserts.
  • Entisols are of relatively recent origin with little or no horizon development. It is often found in areas where the rate of erosion or deposition outpace the rate of soil development, such as floodplains, mountains, and badlands.
  • Gelisols are Weakly weathered soils formed in areas that contain permafrost within the soil profile.
  • Histosols are rich in organic matter are found in coastal areas of lakes, where poor drainage creates conditions for slow decomposition and accumulation of peat (or muck).
  • Inceptisols show moderate weathering and development. Often found on steep topography and overlying erosion-resistant bedrocks.
  • Mollisols. Agricultural soils made highly productive due to a very fertile, organic-rich surface layer.
  • Oxisols are very old, extremely leached, and weathered soils with a subsurface accumulation of iron and aluminum oxides. Commonly found in humid, tropical environments.
  • Spodosols. Acidic soils in which aluminum and iron oxides accumulate below the surface. They usually form under pine vegetation and sandy parent material.
  • Ultisols have subsurface clays that have low native fertility and are often red-hued (due to the presence of iron oxides). Commonly found in humid tropical and subtropical climates.
  •  Vertisols are clay soils with high shrink/swell capacity. During dry periods, these soils shrink and form wide cracks; during wet periods, they swell with moisture.

6 Main Groups of Garden Soils

Soil provides your crops with the vital nutrients, water, and air they need for healthy growth and development. But every garden has its own mixture of minerals, organic and inorganic substances, which largely determines which crops, bushes, or trees can be successfully grown.

Perfect soil conditions for certain crops can be created in enclosed areas, such as raised beds or planters, but for large gardens and farms, it is very important to understand what kind of soil you will have to work with.

There are 6 main groups of garden soils: clay, sandy, silty, peaty, chalky, and loamy. Each has different properties and it is important to know them in order to make the best choice and enjoy a delicious harvest in your garden.

Photos by Michael Feldmann

Clay Soil

Clay soil appears very rock-hard when dry and sticky and lumpy when wet. Clay soil is poorly drained and has few air spaces. In spring, the soil warms up slowly and is very difficult to cultivate. If soil drainage is enhanced, plants will thrive and grow as clay soil can be rich in nutrients.

Clay soil is excellent for growing ornamental trees, fruit trees, shrubs, and perennials. Some early vegetable and berry crops are difficult to grow in clay soil due to its cool, compact nature.

Sandy Soil

Sandy soil feels gritty. This soil is easy to drain, dries quickly, and is very easy to work with it in the garden. Sandy soil heats up quickly in spring and tends to contain fewer nutrients as these are often washed away during wetter periods. Sandy soil requires organic additives for example glacial rock, greensand, kelp meal, and other organic fertilizer mixtures. Mulching is also helpful to retain moisture.

Bulbs, and Shrubs such as Hibiscus, Sun roses, and Tree mallow, grow great on sandy soils. Some examples of fruits and vegetables grown commercially in sandy soils include: strawberries, tomatoes, peppers, lettuce, squash, zucchini, corn, and collard greens.

Silty Soil

Silty soil feels very soft and soapy, retains moisture, and is commonly very nutrient-rich. This soil is great for gardening, is very easy to work with, and can be compacted with little effort. It is a great soil for small gardens or farms as long as there are drainage and maintenance. Mixing compost with organic matter is usually necessary to improve drainage and improve texture while adding nutrients.

Plants that grow well in silty soils are: shrubs, grasses, perennials, climbing plants, and moisture-loving trees such as willow, birch, dogwood, and cypress. Almost all fruits and vegetables can be grown on silty soils.

Peaty Soil

Peaty soil is a very dark soil that appears spongy and moist due to its higher peat content. It is an acidic soil that slows down decomposition and results in fewer nutrients in the soil. In spring, the soil heats up quickly and can hold a lot of water, which usually requires drainage. For soils with a high peat content, it may be a good idea to dig out drainage channels. Peaty soil is perfect for growth when mixed with rich organic matter, compost, and lime to reduce acidity.

The following plants can be grown on peaty soils: Brassicas, legumes, root crops, and salad crops. Shrubs such as Heather, Lantern Trees, Witch Hazel, Camellia, and Rhododendron also grow well on peaty soils.

Chalky Soil

Chalky soil is larger grained and usually stonier than other soils. It drains freely and usually covers chalk or limestone bedrock. The soil is alkaline in nature, which sometimes leads to stunted growth and yellowish leaves – this problem can be solved by using appropriate fertilizers and balancing the pH of the soil. It is recommended to add humus to improve water retention and workability.

Chalk soil is great for growing trees, bulbs, and shrubs such as Weigela, Lilac, Pinks, Madonna lilies, and Mock Oranges. And vegetables such as cabbage, spinach, beets, and sweet corn grow well in chalky soil.

Loamy Soil

Loamy soil, which is a relatively even mixture of sand, silt, and clay, appears slightly moist fine-grained. It has perfect characteristics for growing, almost all shrubs, and lawns. Loamy soil has excellent structure, adequate drainage, moisture retention, full of nutrients, easy to cultivate, and warms up quickly in spring, but does not dry out quickly in summer. Loamy soils require regular replenishment of organic matter and tend to be acidic.

Plants that grow well in loamy soils are: Climbers, perennials, shrubs, and tubers such as Wisteria, Black Bamboo, Rubus, Dog’s-tooth violets, and Delphinium. Almost all vegetables and fruits such as berry crops grow excellent on loamy soils.

Loamy soil is probably the most productive type of soil. However, loamy soils require careful maintenance to prevent drying and depletion. Rotating crops, using mulches, planting green manure crops, adding compost and organic nutrients are essential to retaining soil vitality.

Determining the Type of Soil in Your Garden

There are several tests that help determine the type of soil. The first and simplest one can hardly be considered a test. Though, despite its simplicity it can give an approximate idea of what type of soil you have. Just take a handful of damp soil and rub it with your fingers.

  • Clay soil will feel sticky, slimy and coat the finger with a shiny layer. It can be mounded into many forms and stays in shape.
  • Sandy soil feels gritty and crumbles apart.
  • Silty soil crumbles easy, it is smooth and feels soapy to the touch.
  • Peaty soil is rarely found. It is dark in color and feels spongy when squeezed.
  • Loamy soil is something in between. It has a smooth feel and hold its shape for a short period of time.
  • Chalky and alkaline soils froth when placed in a jar of vinegar.

Another More Accurate Test is the Jar Test

Leave a handful or two of soil on a newspaper to dry. Remove any debris (leaves, bark, rocks, etc.) and crumble the soil to fine particles. Fill a glass jar one-inch deep with the soil. Add water to fill two-thirds of the jar. You can also add a pinch of salt or laundry detergent to better separate the soil components. Shake the jar vigorously. Place it in an undisturbed place to settle for several days.

Check the jar in several days. The particles should settle in layers. Sand settles quickly and forms the bottom layer. The next layer is composed of silt particles. They will settle after several hours. The last and highest layer is formed of clay. It can take several days or more for the clay to settle. A general rule is that when the clay is fully settled the water becomes almost clear. Measure the total amount of soil and then all the layers. Calculate the percentage of sand, silt, and clay.

  • Sandy soil has: 0-10% clay, 0-15% silt, and 90-100% sand.
  • Silty soil has: 7-27% clay, 28-50% silt, and 23-52% sand.
  • Clay soil has: 40-100% clay, 0-40% silt, and 0-45% sand.
  • Loamy soil has about: 20% clay, 40% silt, and 40% sand.

Soil pH

Soil pH also plays an important role in how well your plants grow. Every plant has a preferred soil pH with most growing in slightly acidic to neutral soil with a pH of 6.5 to 7. But it varies from plant to plant.

pH is measured by a number ranging from 0 to 14 with 7 being neutral and getting more alkaline as the number gets larger and more acid as the number gets smaller. Soil pH can range from 5.0 sour (acid) soil to 8.0 sweet (alkaline) soil.

If the soil is found to be too acidic, it may be calcified or enriched with organic matter containing limestone (for example, mushroom soil). If the soil is very alkaline, then you can lower the pH by adding more acidic soil or its mixture with peat, or you can also use manure containing sulfur.

Determining the Soil pH of Your Garden

There are several ways of testing soil pH. You can determine the pH of the soil on the site using a portable pH meter, a test kit, litmus paper, or using vinegar and baking soda. Needless to say, portable pH meters and test kits have instructions included with them. So, the instructions for checking soil pH using the last two methods would be included below.

Test Your Soil pH with Litmus Paper. Using litmus paper to check soil pH is a cheap and accurate method that doesn’t require much. Just add some soil to distilled water and check it with a litmus strip. Compare the color of the strip to a pH color chart. Because the pH of distilled water is 7 neutral the color of the strip will indicate the soil pH.

Test Your Soil pH with Vinegar and Baking Soda. You can also test your soil pH with vinegar and baking soda, collect 1 cup of soil from different parts of your garden and put 2 spoons into separate containers. Add 1/2 cup of white vinegar to the soil. If it sizzles, then you have an alkaline soil with a pH value between 7 and 8. If after vinegar it does not evaporate, add distilled water to another container until 2 teaspoons of the soil becomes cloudy. Add 1/2 cup baking soda. If it sizzles, you have acidic soil, most likely with a pH between 5 and 6.

If your soil does not react at all, it is neutral with a pH of 7, then this is ideal soil.

Plants That Help Determine the Type of Soil

Many observant farmers can easily determine fertility, acidity, moisture, and soil type simply bylooking at the weeds that grow on it. Weeds are also good indicators of soil condition. Knowing the type of plants that grow on the soil not only helps determine its fertility and structure but also helps determine which crops will grow best on the soil.

Illustration by Paul Anderson

Plants That Indicate Fertile Soils: Weeds that indicate fertile soil include: Nettle, field mustard, Small-Flowered Galinsoga, Amaranth, Chicory, Common Groundsel, Lambsquarters, Chickweed, Knapweed, Purslane, Ostrich Fern, and Horehound.

Plants That Indicate Poor Soils: Weeds that indicate poor soils include: Dandelion, Annual Bluegrass, Crabgrass, Little Blue Stem, Ox-Eye Daisy, Moss, Common Mullein, Pearly Everlasting, Queen Anne’s Lace, Plantain, Ragweed, White Clover, Mugwort, Sheep Sorrel, and Yarrow.

Plants That Indicate Sandy Soils: Weeds that indicate sandy soils are: Rabbit Foot Clover, White Cockle, Bindweed, Goldenrods, Cornflower, Corn Spurry, Little Blue Stem, toadflax, Mustard, Sheep Sorrel, and Yarrow.

Plants That Indicate Clay Soils: Weeds that grow on clay soils are: English Daisy, Chicory, Dandelion, Plantain, knotweed, Prostrate Knotweed, Quackgrass, Colt’s-foot, Broad-leafed Dock, creeping buttercup, Stinking Mayweed, Annual Sow-thistle, and Canada Sow-thistle.

Plants That Indicate Acid Soils: Land with acid soil will have commonly have the following weeds: Dandelion, Nettle, Ox-Eye Daisy, Rabbit Foot Clover, Moss, Common Mullein, Eagle Fern, Cornflower (With pink flowers), Pearly everlasting, Sheep Sorrel, Silvery Cinquefoil, Hop Clover, Colt’s Foot, English Daisy, Dock, Horsetail, Knotweed, Hawkweed, Prostrate Knotweed, Knawel, Lady’s Thumb, Stinking Mayweed, Wild Pansy, Wild Radish, Plantain, Corn Spurry, Wild Strawberry, and Sundew.

Plants That Indicate Alkaline Soils: A soil supporting: Chicory, Mustard, Hare’s Ear Mustard, White Mustard, Campion, Cornflower (With Blue Flowers), Chickweed, Queen Anne’s Lace, Corn Chamomile, Black Henbane, Creeping Bellflower, Wormseed Mustard, Field Peppergrass, Perennial Sow-thistle, Stinkweed, and Nodding Thistle is alkaline.

Plants That Indicate Wet Soils: Weeds that indicate wet soils are: Ox-Eye Daisy, Dock, Goldenrod, Horsetail, Knotweed, Coltsfoot, Creeping Buttercup, Swamp Aster, Hedge Bindweed, Skunk Cabbage, Corn Chamomile, Colt’s Foot, Cotton Grasses, Low Cudweed, Short-Awned Foxtail, Marsh Hedge-Nettle, False Hellebore, Joe-Pye Weed, Lady’s Thumb, Moss, Horseweed, Smartweed, Poison Hemlock, Broadleaved Meadowsweet, Plantains, Rushes, Tansy Ragwort, Ragged Robin, Sedges, Silverweed, Garden Sorrel, Thyme-Leaved Speedwell, Perennial Sow-thistle, and Spotted Water Hemlock.

Plants That Indicate Dry Soils: Weeds that indicate dry soils are: Little Blue Stem, Mustard, Queen Anne’s Lace, Sheep Sorrel, Yarrow, Agrimony, Night-flowering Catchfly, Silvery Cinquefoil, Rabbit Foot Clover, White Sweetclover, Prostrate Pigweed, Common Speedwell, Leafy Spurge, and Russian Thistle.

Plants That Indicate Heavy Metals or Possibly Gold in the Soil: Land with Heavy metals or gold will have commonly had the following weeds: Highland Bent Grass, Hairy Goldenrod, Willow, Rapeseed, European Pine Code Lepidella (mushroom), Ink Stain Bolete (mushroom), Sarcosphaera coronaria (mushroom), Sunflower, Ragweed, Armeria maritima, Blue Sheep Fescue, Roundleaved Pennycress, Common Wheat, Bassia scoparia, Campion, and Red Clover.

Michael Feldmann is a farmer and writer in Oklahoma, who studies agriculture and has worked as a journalist for magazines and newspapers around the country. His writing has been published in Acres USA, Rural Heritage, Farming magazine, Farmers Weekly, Permaculture magazine, MOTHER EARTH NEWS, and as a column in Poultry World. Read all of Michael’s MOTHER EARTH NEWS posts here.

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