Guide to Soil Characteristics

It is important that you understand the soil characteristics of your garden if you want to make the most of your planting endeavors.
By Charles P. Mazza
June 2014
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This soil is approximately 45 percent sand, 5 percent silt and 50 percent clay. Organic matter is negligible.
Photo courtesy PALS Publishing
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Have you ever hesitated before planting, unsure whether your garden plan is right for the space you have to use? If that’s the case, you need to check out Site Assessment for Better Gardens and Landscapes (PALS Publishing, 2013), a great tool for learning how to evaluate the characteristics of a site and determining which plants will thrive. Author Charles P. Mazza offers advice and strategies for gardeners novice and expert alike, with more than thirty hands-on activities and fifty color photos. This excerpt comes explains how to determine the soil characteristics of your site, and how that affects your selection of plants.

You can purchase this book from Capper's Farmer store: Site Assessment for Better Gardens and Landscapes.

Why is Knowing Soil Characteristics Important?

Soil can make or break a garden or landscape because it supplies water and nutrients to plants through the plants’ roots. Too much or too little of either can hurt plant health. The physical and chemical composition of soil varies from place to place and can even be different within the same yard. Considering soil characteristics will help you select plants that will thrive.

The physical composition of soil is determined by the soil’s texture — the relative amounts of sand, silt, and clay in the soil. Knowing the soil’s physical composition will help you make informed decisions later in the process. The chemical composition of the soil — the levels of nutrients present and the soil pH — affects nutrient uptake by plants. For example, some plants (such as blueberries and rhododendrons) require acidic soil.

Activities

1. What’s the physical composition of my soil? — Soil Sedimentation Test

Materials
• Pointed shovel
• Bucket
• Sealable plastic bag
• Pint-sized glass jar with tightly fitting lid — the narrower the better (an olive jar works well)
• Kitchen timer, watch, or electronic timer
• Powdered dishwasher detergent
• Ruler
• Masking tape
• Site assessment notebook 

Estimated Time: 20 minutes of collecting, observing, and recording. Overnight for drying the soil. It may take 2–3 days to complete the test.

1. To get a good overview of soil characteristics, take soil from 10 locations around the study area. Dig holes 6 to 8 inches deep. Then take a vertical slice of soil from the edge and place it into the bucket. Mix them all together. Measure one cup of mixed soil for this first activity. Save another cup in a sealed plastic bag for the next activity on measuring the soil’s pH.

2. Let the soil dry and remove stones, roots, grass, or other debris.

3. Apply a strip of masking tape vertically to the pint-sized glass jar. (Later you’ll mark levels on the tape.)

4. Add one cup of dried, debris-free soil to the jar. Add water until the jar is about 2/3 to 3/4 full.

5. Screw on the lid and shake well to put the soil into suspension.

6. Add one teaspoon of powdered dishwasher detergent. Shake again.

7. Place the jar on a flat surface where it can remain undisturbed for several days. Set the timer for one minute.

8. At the end of one minute, mark on the masking tape the level of soil particles that have settled to the bottom. This will be the sand component.

9. Reset the timer. At the end of 2 hours mark on the masking tape the level where the soil particles have settled to the bottom. This second layer is the silt component.

10. It may take several days for the clay component to settle out. Mark the level tentatively after two or three days. Check and mark daily after that. If the level doesn’t rise from one day to the next, use that line as your final level. Even after several days, the water will remain cloudy as a small percentage of clay particles will remain in suspension.

11. The layers reflect the percentage of sand, silt, and clay in the soil. Divide the thickness of each layer by the total height of settled soil (not the height of the water, just the settled soil). Multiply by 100 to find the percentage of sand, silt, and clay. Record the percentage of sand, silt, and clay in your notebook.

12. Any darkly colored material floating in suspension in the water is organic matter. Estimate whether you have none, a little (negligible), or a substantial amount. Estimating organic matter is difficult because it has many more air pockets and is looser than the mineral soil sediment. Record observations in your notebook.

People with experience in different types of soils also estimate texture by manipulating it in their hand and feeling it.

2. What is the pH — acidity or alkalinity — of my soil?

Materials
• Soil saved in sealable plastic bag from first activity
• Site assessment notebook

Estimated Time: Collecting time is included in the first activity; waiting time at lab will vary.

Use the soil collected during Activity 1 in this step. If the sample is wet, spread the soil in a thin layer on an aluminum pie pan, clean wrapping paper, or waxed paper, and allow it to dry out at room temperature. Remove stones, roots, and debris.

While home pH test kits are available from garden centers, many gardeners struggle to get accurate and consistent results. Contact your local Cooperative Extension office to see if they operate a lab that can test soil pH. If they can’t, ask them for instructions to send your sample to a reputable soil lab.

Record the soil’s pH in your notebook. pH may vary around the property. When you consider locations for plantings, test the location’s pH.

3a. Visual Observations

Soil Appearance

Materials:
• Long-handled, pointed shovel
• Site assessment notebook

Estimated Time: 30 minutes

In this activity, you will examine the soil horizons or layers. It is especially useful if there has been recent construction activity. If you are not aware of past construction activity, choose an undisturbed location at random to get a better idea of topsoil depth.

Dig a pit approximately two feet deep and two feet wide. Soil layers that are noticeably lighter in color than lower layers indicate that subsoil has been spread on top of the original soil. Conversely, the absence of a rich brown, organic layer at the top may indicate that the topsoil has been removed. In undisturbed soils, estimate the depth of topsoil. Record the observations in your notebook.

3b. Visual Observations

Soluble Salt

Materials:
• Site assessment notebook

Estimated Time: 5 minutes

Look (particularly near walks and parking areas in early spring) for white powder that has precipitated from the soil surface. Deicing salts linger and can cause damage to plants. There are other sources for soluble salts, but it is difficult see them. If you suspect a problem, more extensive lab tests may be warranted. Record observations in your notebook.

Using What You Found in This Step

The percentages of sand, silt, and clay can indicate which component is most dominant. A soil that has a high percentage of sand is sandy; high silt is silty; and high clay is clayey.

In soil, textural type is a description of relative proportion of particle sizes. Many of our garden soils are some variation of loam — some are moderately fine, some are medium and others are moderately coarse. The variations come from the amount of sand, clay, or silt that the loamy soil contains.

In some areas, garden soils have soil textures other than loam. Silty soils feel somewhat like flour. Clayey soils have predominately small or fine particle size, but they will clump up easily and, when wet, will feel like you can roll and mold them like...well, clay. Sandy soils are coarse to the touch. The textural differences give an indication of drainage potential, ability to hold nutrients, and ability for plant roots to develop. Sandy soils drain well, but hold nutrients poorly; clayey soils drain poorly, but retain nutrients well. Clayey soils (and, to some extent, silty soils) compact more easily than sandy soils, making it more difficult for roots to develop.

Use the simplified soil texture triangle to determine soil textural type. Find the percentage of clay, silt, and sand from your soil sedimentation test. Mark the point of each percentage on this triangle. From the percentage clay number, draw a straight line from it, left to right, parallel to the bottom of the triangle. From the percentage silt number, draw a straight line from it to the bottom left, parallel to the left side of the triangle. From the percentage sand number, draw a straight line from it to the top left, parallel to the right side of the triangle. Where the three lines meet is the general category of your soil textural type.

The soil shown in this photo, 5% silt, and 45% sand. So, it is a clayey soil type. Using the results of your sedimentation test, locate your soil on the triangle. In your notebook, record whether the soil is clayey, loamy, sandy, or silty. For a more precise soil textural classification, refer to the USDA soil textural class triangle in the glossary.

Soil is what it is. Only in extreme cases is it unable to support plant growth. You may garden or landscape with whatever soil you have and make choices accordingly. For instance, if you have a soil high in clay, you may choose plants that tolerate poorly drained soils. Or you may add organic matter to your soil, which can help improve drainage. Organic matter also improves sandy soil, helping it retain more water and nutrients. Or you could choose to grow plants that tolerate drought and low nutrient levels.

Organic matter, an important component of healthy soils, breaks down continuously, and needs to be replenished. One source of organic matter is topsoil sold in bags or by the truckload. Other sources are compost, well-rotted manure, or peat moss. All are mixed into existing soils. Incorporate only thoroughly composted or decomposed manure into the soil. Otherwise, it will compete with plants for nutrients as it decomposes.

The results of a pH test indicate on a scale of 0–14 whether your soil is acidic, neutral, or alkaline — the lower the number, the more acidic the soil. A pH of 5.5 is 10 times more acid than a 6.5 pH, a 4.5 pH is 100 times more acidic than a 6.5 pH. An acid soil will not burn people, pets, or plants.

The soil pH is important information for plant selection and site preparation. Most plants prefer a soil pH between 6 and 7. Rhododendrons, azaleas, hollies, and blueberries, prefer a pH between 4.5–5.8. Changing pH can be difficult, especially after planting. Lowering pH is harder than raising it.

Lime is used to reduce the acidity (raise the pH) of soil. Sulfur is used to increase acidity (decrease pH). Application rates are based on recommendations from a soil test. Soils tend to resist pH change and amendments may need to be added each year. If the pH is extremely different from the new planting’s needs, it may be necessary to start amending the soil a year before you plant. Check with your Cooperative Extension office for advice on altering soil pH in your area.

In this step, the soil sample used to measure the pH was a mixture of samples taken from around the site. When planning plantings for a subsection of the site, test for pH and nutrients to determine if soil characteristics are favorable.

Instead of trying to change the pH, consider other options. You can choose a plant that will thrive without changing the soil’s pH. For example, instead of lowering the pH for blueberry plants that prefer a pH of 4.5 and 5.8, choose currant or gooseberry plants that thrive in soil with a pH of 6.5. Or, you can create a raised bed and bring in the soil with the right pH and other factors to grow the plants you desire.

If you have found evidence of soluble salts near driveways, sidewalks, or roads, flush salted planting areas with water in the spring. Use plant-friendly deicing salts or coarse sand for traction during winter. For plantings near roadsides, choose salt-tolerant plants or install a burlap fence to shield against splashing road salt. A few examples of salt-tolerant trees are honey locust, Austrian pine, and red oak. Trees that do not tolerate soluble salts include sugar maple, white pine, and pin oak.

Want to learn more about site assessment? Read Helpful Tips for Site Assessment.


Dumping

Look for signs that paint, oil, or gasoline have been dumped on the property. Signs may include only weeds growing in an area or soil that is completely bare. Observations like this are best made occasionally over time rather than just once. Plants may not grow in an area if dumping has been excessive.

Record observations in your notebook.


Soil Health

There is growing interest worldwide in improv­ing soil in all its aspects, especially as it affects the economy, including farming. While traditional soil science has focused on soil chemistry and the physical characteristics of soil, there is now more focus on the biology of soil, including its micro­organisms. The biology of soil plays a great role in improving plant productivity and environmental quality. Soil health emphasizes the integration of biological, chemical, and physical measures of soil quality. Awareness of this will help home gardeners think of soil as a dynamic plant growing medium instead of just dirt.


Plants Mentioned in Step 8

The common name is followed by the scientific name and then additional information if needed.

Austrian pine – Pinus australis

Blueberry – Vaccinium sp. – there are about 16 species that may be considered blueberries. The most common blueberry plants are Vaccinium corymbosum (highbush blueberry) and Vaccinium angustifolia (lowbush blueberry).

Currant – common currants grown in the U.S.A are red currants (Ribes rubrum) red currant and white currants (Ribes glandulosum)

Gooseberry – Ribes uva-crispa

Honey locust – Gleditsia triacanthos

Pin oak – Pinus palustris

Red oak – Quercus rubrum

Rhododendron – Rhododendron sp. – a genus of more than nine-hundred species, which includes plants with the common names of azalea and rhododendron. When used as a common name, rhododendron refers to shrubs with large clusters of flowers.

Sugar maple – Acer saccharum

White pine – Pinus strobes


For Further Reading

Building Soils for Better Crops, 3rd Edition, Fred Mag-doff and Harold van Es. Sustainable Agriculture Publications, Waldorf, MD 2010.

Composting to Reduce the Waste Stream, NRAES- 43, Robert Kozlowski, NRAES, Ithaca, NY, 1991.

Secrets to Great Soil (Storey’s Gardening Skills Illus­trated), by Elizabeth Stell, Workman Publishing Co., New York, 1998.

Soil Science Simplified, 4th Edition, by Helmut Kohnke and D.P. Franzmeier, Waveland Press, Prospect Heights, Illinois, 1995. Includes technique for estimating soil texture by manipulat­ing it in the hand.

Start with the soil: The Organic Gardener’s Guide to Improving Soil for Higher Yields, More Beautiful Flowers, and a Healthy, Easy-Care Garden, Grace Gershuny, Rodale Press, Emmaus, PA 1995.

Visit Cornell University's College of Agriculture and Life Sciences for a link to the web sites below, and all web sites mentioned in this book.

Organic Matter

Using Organic Matter in the Garden, From Cornell Cooperative Extension by Charles Mazza, Sally Cunningham, and Ellen Harrison.

Improving Garden Soils with Organic Matter, From Oregon State University by Neil Bell, Dan M. Sullivan, Linda J. Brewer, and John Hart.

Salt-tolerant Trees

From Recommended Urban Trees: Site Assessment and Tree Selection for Stress Tolerance, Urban Horti­culture Institute, Cornell University, 2009.

Salt Sensitive Trees

From Recommended Urban Trees: Site Assessment and Tree Selection for Stress Tolerance, Urban Hor­ticulture Institute, Cornell University, 2009.

Soil Basics

From the Cornell Garden Based Learning, Department of Horticulture, Cornell University.

Soil Health

Cornell Soil Health website. Includes a soil health assessment manual — primarily for farmers, but instructive to others. From Cornell University.

Soil Health. Includes a section that explains how soils are alive. From the University of Western Australia.


Reprinted with permission from Site Assessment for Better Gardens and Landscapes by Charles P. Mazza and published by PALS Publishing, 2013. Buy this book from our store: Site Assessment for Better Gardens and Landscapes.


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Post a comment below.

 

RENEEB
9/9/2014 11:57:20 AM
Very interesting article. I have a question about the effect of water on soil. We live in an area with very clay soil. It is so fine in particle that when you dig a hole (with great effort) water will sit in the hole for days and won't percolate down. So we built beds and brought in soil because we wanted to plant right away. However, doing a water test revealed that our well water was very alkaline. This is also evidenced by the fact that calcium carbonate deposits remain when water goes down in the local creeks. We also have very hot weather (often in the triple digits for days at a time). My vegetables don't flower well, have high percentage of male to female flowers. My yields are very low. I can grow sweet basil and sunflowers like gangbusters. Is my water ruining the pH in my boughten soil?








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