Soil Acidity Test

Earth Science Unit Study
Week 17: We tested the acidity of garden soil with cabbage water.

Acidity levels in soil are one variable which can lead to a successful or unsuccessful garden. Most plants prefer neutral PH levels around 7. Soil located under pine trees is often acidic and using nitrogen fertilizers can lead to acidic soil issues.

At our previous residence there was a pine tree located very close to a plum tree which never produced any plums. One year the pine tree was chopped down, and the next year the plum tree was loaded. At our current residence there was a similar incident. A garden located near a pine tree produced very little and contained few worms and life. One year the pine tree became a Christmas tree for the local church and the next year the garden thrived. 

Water dyed dark purple, which is produced upon boiling red cabbage in water can be used to determine if a substance is basic or acidic. Bases will turn shades of blue and green, while acids turn pink. Here's a color chart for cabbage water PH.

Before testing the soil, we used some of the cabbage water to test milk, dish soap, lemon juice and vinegar. The results indicated that the milk had a PH around 4, dish soap around 9, and lemon juice and vinegar around 1.

Like so many science experiments, this project didn't work well the first time and needed to be repeated. Six samples of soil were gathered from around the yard and cabbage water was added to each one. Unfortunately some of the containers used to gather soil had holes in the bottom and the water ran right out. (ha, ha, the joke was on me I think.)  In addition, the colored containers created difficulty in viewing the samples.

Repeating the experiment, water bottles with the tops removed were used. They worked much better.

The results indicated that all six samples were basic with acidity levels around 9.

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  1. You can also pour vinegar on a soil sample, to see if it will fizz - indicating it is a base.

  2. Great project. Adding cabbage to my grocery list!


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