Gardening with Deb: Understanding your garden soil

Deb Babcock/For the Steamboat Today
Deb Babcock

CSU Master Gardeners are available to answer your gardening questions 10am-1pm on Thursdays continuing through the gardening season. Call 970-870-5241, email csumgprogram@co.r... or visit them in the Extension Office, 136 6th St.

We often hear the soil in our Yampa Valley gardens is somewhat alkaline. What exactly does that mean, and what should we do about it?

The acidity or alkalinity (pH level) of your soil will affect plant growth by controlling how easily nutrients can be taken up from the soil by your plants. For instance, in acidic soils, nitrogen (a very important plant nutrient) is not easily converted to a form plants can use. The same holds true for phosphorus and potassium to varying degrees and for micronutrients to lesser degrees.

Soil pH ranges from 0 (strongly acid) to 14 (strongly alkaline), with a reading of 6.5 to 7.0 indicating that the soil is neutral — good for most plants. Most Colorado soils tend to have pHs greater than 7, although my soil test report from Colorado State University indicated a pH of 6.2 for my garden soil located a few miles north of town.

If soil has a pH value higher than 8.5, it means that the soil has too much sodium in it, making it difficult to grow most plants. To reduce soil alkalinity, you can apply sulfur or aluminum sulfate. For acidic soil, gardeners often apply wood ash or limestone to bring it more into balance.

The only way to determine the pH level of our garden soil is to have a soil test conducted. This is done at testing laboratories, such as the lab at Colorado State University (970-491-5061). Once you know your soil pH, you can make adjustments as needed. The Master Gardeners at the Routt County Extension office can help you determine which amendments to use and how much to add to your soil to make your garden more fertile. Stop by the Extension Office on 6th Street any Thursday morning, and Master Gardeners will be on hand to answer your questions.

As a garden goes through several seasons, the soil tends to become more acidic, especially when commercial fertilizers are used (as opposed to using compost and tilling in old plant material to add nutrients). That’s because most fertilizers contain salt, which can build up in your garden soil.

When you have a soil test conducted, the lab will analyze your soil for pH, salts, lime, organic matter and nutrients such as nitrate, phosphorus, potassium, zinc, iron, manganese and copper. The report will make recommendations for the addition of organic matter, nutrients or other improvements if needed. The cost is minimal, and it takes about a week for results, depending upon how busy the lab is at the time you submit your sample.

Consider having a soil test conducted every three to four years since your soil composition and pH level can change as the garden matures.

Deb Babcock is a Master Gardener through the CSU Extension Routt County. Questions? Call 879-0825 or email

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