Smarter Gardening through Soil Testing and Improvement

By Lori Anderson, Hennepin County Master Gardener

June 2024

At Dowling we have plots that have been gardened by many, many other people in its 80-year history. We enter with little knowledge of the chemical or fertility status of our plots or how it may affect what we want to grow. Sometimes we think we know the soil is healthy just by looking at it. If it retains water and has good tilth (water permeability and retention, friable or crumbly texture, good drainage), we feel we lucked out and may not have to do much to improve its health. However, that tells us nothing about its pH, for example, or whether it is adequate or deficient in certain nutrients needed to grow healthy vegetables. Evaluating soil pH and fertility can be very helpful in diagnosing plant problems.

We are fortunate to have the Soil Testing and Research Analytical Lab nearby at the University of Minnesota’s St. Paul campus. They provide an easy way to learn more about our soil’s health by taking basic soil nutrient measurements in addition to providing fertilizer recommendations. It’s so easy: you take a 2-3 cup soil sample (using a clean sealable jar, deli container, or plastic bag), complete a form indicating the type of testing you’re requesting, and either mail or deliver it to the St. Paul campus (see below) along with the payment. Here's complete information on the process, including a PDF of the request form and a video for how to take a soil sample. 

The regular test costs $20 and includes the percent of organic matter, phosphorus, and potassium; the pH level; and their estimate of soil texture. Lead and salts testing are options, as are trace elements, although the latter is not considered necessary for vegetable gardens in Minnesota. Testing does not measure nitrogen because it is very mobile (changeable) in the soil so testing would not produce reliable results. Based on the intended use of the soil-- vegetables in most cases at Dowling--the test results will also indicate fertilizer requirements. 

Don’t be surprised if your test results show that you have an “off-the-chart” high level of phosphorus! This is very common in our area and not even a problem as long as it stays put in the soil. Problems arise when it blows away or erodes, causing polluted waterways and ultimately algae blooms. And pat yourself on the back if it indicates you have high organic matter! Soil testing is recommended every three years since your efforts can make measurable differences in that time.

A note on soluble salts testing: An overuse of compost or composted manure over time can result in a buildup of salts and elevation of soil pH (alkalinization) due to high concentrations of magnesium and calcium. Alkalinization can bind up certain nutrients so they become unavailable to the plant. Salts buildup can damage plant roots and soil structure, and can sometimes be alleviated through intense irrigation to flush them out or by acidifying irrigation water. This extra test costs $8.50. Considering how much compost and composted manure we are fortunate to have access to at Dowling, this might be a useful test to invest in when you deliver your soil sample.

I hope you consider taking advantage of this wonderful benefit at the University, and realize the investment you’re making to garden smarter and more effectively!

UMN Soil Testing Lab address: 

Room 135, Crops Research Building

1902 Dudley Ave (there is FREE PARKING on Dudley at the curb for delivering soil samples)

St. Paul, MN 55108

M-F 8 a.m.-4:30 p.m.

(612) 625-3101

soiltest@umn.edu