Rex’s tips: Soil types, analysis, temperature

Photo courtesy of Mattox

SOUTHERN UTAH – There is a cheap and easy way to test your own soil. No need to pay someone to test it for you. Here is how to test your own soil.

First, find an empty, clean quart jar – an old mayonnaise jar works very well for this test. Fill the jar about 2/3 full with dirt from your garden.

Next, fill the jar with tap water until the jar is nearly full, leaving about 1 inch of air space at the top. Screw on the lid and shake it vigorously for a minute or two, until all the soil particles are broken down into suspension in the water.

Allow the jar to sit undisturbed all day, or all night. The sand will be at the bottom, the silt will be on top of the sand, and the clay will be the top layer. The percentage of each layer tells you what kind of soil you have. You will be able to see the separation and difference between sand, silt, and clay. The sand will actually drop to the bottom within a couple of minutes, and the silt will drop within 5-10 minutes; the clay will take longer. You may also have some large pieces of compost material on top of the clay. You are not measuring compost material so ignore it for this test.

Sandy soils are typically comprised of approximately 80 – 100 percent sand, 0 – 10 percent silt and 0 – 10 percent clay by volume. Sandy soils are light and typically very free draining, usually holding water very poorly due to very low organic and clay content.

Loam soils are typically comprised of approximately 25 – 50 percent sand, 30 – 50 percent silt and 10 – 30 percent clay by volume.  Loam soils are somewhat heavier than sandy soils, but also tend to be fairly free draining, again, due to typically low organic content.

Clay soils are typically comprised of approximately 0 – 45 percent sand, 0 – 45 percent silt and 50 – 100 percent clay by volume.  Clay soils are not typically free draining, and water tends to take a long time to infiltrate. When wet, such soils tend to allow virtually all water to run-off. Clay soils tend to be heavy and difficult to work when dry.

The ideal soil is 10-20 percent clay, 40-50 percent silt, and 30-40 percent sand. Very good soils exist with varying percentages, as long as the clay does not get above about 30 percent. Clay is not all bad, it has more nutrients than either sand or silt, and it retains water well. It is also healthier for plants than either sand or silt. Still, too much of it is bad.

So what can be done about heavy clay soil? Bring in humus, lots of it; sawdust, leaves, lawn clippings, pecan shells – do not put walnuts in the garden; almond shells, and vermiculite. I dump all my pecan shells in my garden. They take awhile to decompose, but they are very good for the soil.

Fireplace and wood stove ashes should not be put in the soil in the western United States.

Till the compost as deep as you can. One tilling will not suffice, you should till your garden with some frequency anyway.

Compost can be purchased in bulk from the landfill or the Washington County Fairgrounds in Hurricane. They will fill your pickup or trailer for you, and the price is far better than buying it bagged from the nursery, but that can be done too if you prefer. It may take you two or three years to actually correct a clay soil problem, so be patient.

A note of caution to gardeners who attempt to improve clay soils by amending them with sand: This is a bit risky unless the sand is larger, granular sand. Otherwise, additions of sand to clay soil can create a cement-like creature that resists root growth and impedes the flow of air and water. So humus is the safe approach.

Here is a reference table for soil temperature. As you can see, soil temperature needs to be between 40-85 degrees; outside this range, nothing grows. It is either too cold or too hot.

The home gardener cannot do a lot about soil temperature, but there is no point in planting anything if the soil temperature is below 40 degrees, and why mid-summer gardens tend to degrade rapidly—it’s just too hot.

Soil Temperature

Conditions during growing season

Less than 40 F

no growth, bacteria and fungi are not very active

40 F to 65 F

some growth

65 F to 70 F

fastest growth

70 F to 85 F

some growth

above 85 F

no growth

A note about pesticides: If you spray your lawn or other plants in your yard then cut and compost, you will inevitably have some residual chemicals in your compost. Commercial fertilizers are not in any way harmful, but if you spray your lawn for bugs, or to kill weeds, then cut your grass, and compost it in your garden, you will have some of those chemicals in your garden.

And certain garden crops should never be tilled into your garden, or composted; these plants are tomatoes, squash, cucumbers and melons.

Why? Tomato plants are prone to various diseases and it’s best to just avoid the problem. The cucurbits – cucumbers, squash, and melons – all attract a lot of bugs, aphids, squash bugs, etc, and their eggs are all over those plants. If you leave them in the garden, and till them in, you significantly increase the likelihood of a strong squash bug and aphid population later. I recommend gathering up all your vines and tomato plants, and stuffing them in your big mouth dumpster and let them be hauled to the landfill.

You should also be careful not to dump weeds and grass seed into your garden or compost. Many weed seeds will survive composting, and mowing a Bermuda Grass lawn and dumping the clippings into your garden will guarantee you will be tilling in thousands of Bermuda grass seeds—so beware.

email: [email protected]

twitter: @STGnews

Copyright 2012 St. George News.

Free News Delivery by Email

Would you like to have the day's news stories delivered right to your inbox every evening? Enter your email below to start!


  • John April 12, 2012 at 8:55 pm

    A word of caution, this test will demonstrate the texture of the soil only. Salt & Nutrient content in reserve or soluble (available form) are only measured by laboratory testing. That said, the texture of soil can be very helpful in establishing watering schedules, too.

  • Top Soil April 16, 2012 at 5:20 am

    Very informative and well written. Thanks for publishing it.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.