The pH Factor in Gardens

Oh, dear. This has become a chemistry lesson. I've suddenly gotten interested in the pH of my soil. It all started after deciding to enlarge my garden...

Santa Fe Greenhouses Greensand
Item # 99736 		Soil Mender Jersey Greensand

each $16.95
  • Topic: Soil
  • Author: Cindy Bellinger
  • Keywords: soil pH, PH, ph, soil, acidic, akaline, neutral, soil condition, adjusting pH
  • Date: September 2005

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Oh, dear. This has become a chemistry lesson. I’ve suddenly gotten interested in the pH of my soil. It all started after deciding to enlarge my garden and do things right. Like get the right plants in the right places and make sure everyone is happy.

The term “pH” was coined in 1909 by a Danish chemist, Soren Sorensen, in a paper about the effect of Hydrogen on the activity of enzymes. He called the effect pH, for pondus hydrogenii or “potential hydrogen.” The terminology refers to acidity due to a predominance of hydrogen ions in a water solution.

So what’s this have to do with soil?

Soil Condition

pH refers to the acidic or alkaline conditions and is measured using a pH scale between 0 and 14. The acidic end ranges from 0-7; alkalinity ranges from 7-14. If soil is too acidic or alkaline, plants cannot utilize the nutrients they need.

Fourteen of the seventeen essential plant nutrients are obtained from the soil. Before a nutrient can be used by plants, it must be dissolved in the soil. Most minerals and nutrients are more available in acid soils than in neutral or slightly alkaline soils. The soils in Santa Fe are very alkaline. One product we recommend that lets plants absorb more iron is Ferriplus.

Measuring pH Levels

The most accurate method of determining soil pH is by a pH meter. Basically, the test measures the amount of lime (calcium) contained in the soil. For best results make sure to sample dry soil. And to be double sure, check your soil more than once.

The best time to test your soil is in the late fall. This allows time to make adjustments before planting again, since soil corrections may take a few months.

Generally, soils in moist climates tend to be acid and those in dry climates are alkaline. A soil with a pH lower than 7.0 is an acid soil and one with a pH higher than 7.0 is alkaline.

Adjust planting beds to suit the plants to be planted in them, and keep in mind that different plants require different degrees of soil acidity.

Adjusting Soil pH

Once you have determined the pH you can amend the soil. It is generally easier to make soils more alkaline than it is to make them more acid. To lower the soil pH and make it more acid, add sulfur. The sulfur should be thoroughly mixed into the soil before planting. Sawdust, composted leaves, wood chips, cottonseed meal and leaf mold will also lower soil pH. Our garden center also carries Greensand and Soil Mender Cottonseed Meal, which help lower pH.

To raise the soil pH and make it more alkaline, add lime. The addition of lime provides two nutrients, calcium and magnesium. Lime also makes phosphorus more available to plants and increases the availability of nitrogen.

It is difficult over the long term to keep alkaline soils acidic and vice versa. So it is best to match plant preferences to the natural pH of your native soil. This is especially true when planting large shrubs and trees whose roots spread over huge areas, too large of a soil volume to treat and maintain.

Of course, all this is way over my head. But I’m going ahead and testing and amending and choosing my plants accordingly. What happened to the good ol’ days when I was a little more naive?