A Guide to Testing Garden Soil

Now’s the time to evaluate the soil in your vegetable beds. Soil texture and richness are fundamental to your vegetable garden’s success and testing is something that should be done on a regular basis. 

The value of performing a soil test on your garden is the information you gather will help you make informed decisions on soil amendments and fertilizers, as well as identify potential crop production problems. The key elements affecting our soils are physical structure, including the amount of clay content versus organic material and soil pH. Soil fertility and availability of nutrients also has an impact on crop production.   

Whether you’ve experienced specific problems, such as Tomato Blossom End Rot or you’ve been disappointed in your garden’s overall yields, it’s important to establish a baseline of your garden soil, to know how to proceed to improve your soil.  

Testing your garden soil can be accomplished at home using soil test kits or soil samples can be sent to a professional testing lab for analysis.  

If you decide to use a lab, you can send a sample to the Colorado State University Soil Testing lab for a more intensive evaluation of your soil. The CSU soil testing lab has moved to: 

Soil, Water, and Plant Testing Lab 
4817 National Western Dr. 
Denver, CO 8021 

For more information, follow this link: 

Soil, Water and Plant Testing Laboratory - Soil Testing Lab (colostate.edu) 

If you decide to test your garden soil at home, it’s important to include a test that will measure the acid-alkaline balance, known as soil pH level.  

Soil pH affects the availability of nutrients to vegetable plants, as well as the microbial activity in your soil.  No matter the quality of the fertilizer or supplements you apply, tomato and vegetable plants can’t use them if the pH is too high.  Soil pH is a measure of the acidity or alkalinity of a soil. On the pH scale, 7.0 is neutral, above 7 is alkaline, also called basic or “sweet”. Below 7 is acidic, sometimes called “sour”. Most plants prefer a pH of between 6.0 and 7. Our soils are typically greater than 7.

This soil check kit is an easy and quick way to check the pH levels in your garden.  Begin by adding the contents of the green capsule in the test tube. Next, add a small amount of soil and fill the capsule with water. Put the cap back on the tube and shake vigorously.  Match the color of the tube to the chart to determine the pH of your soil.  Home test kits are also available to measure the Nitrogen, Phosphate and Potash levels in your garden beds. 

Soil test meters are also available. Some are single function, such as pH only. Others are multi-function, testing pH, as well as nutrients. 

 

In addition to pH and nutrient levels, the structure, physical makeup and organic content of your soil has a direct impact on your garden’s productivity. The Jar Test is a quick, easy way to help you determine the structure and physical makeup of your soil.

You’ll need a clean jar with a lid, in this case a peanut butter container. Put 4-5 ounces (about 147.87 ml) of soil in the bottom of the jar. Add enough water to fill the jar 2/3 full.  Add a drop or two of dishwasher soap. Put the lid on and shake well, then let the jar sit undisturbed for 24 hours.

You’ll see that the soil has settled into layers. The first layer will be sand. The second layer will be silt, followed by clay, a layer of suspended clay, then a small amount of organic material, floating at the top. Typically, you’re going to see a small amount of sand and silt, a large percentage of clay and a small amount of organic material.

As you add more organic material to your garden, your test results will look more like the jar in the middle. The jar on the right illustrates a well-amended garden soil: dark and rich, with more organic material suspended in with the clay. To improve your garden soil and lower the pH, we recommend you add two to three inches of locally produced organic material to your garden in the spring and again in the fall. 

Whether you choose to do-it-yourself or send a sample to the lab, once you’ve received your test results, bring the report in. We’ll help you choose the products you need to implement the changes recommended in your report.