Soil pH Testing Garden Science

One head of red cabbage

A pot for boiling and a strainer

Clear cups — one for each soil sample (at least 3-4)

Soil samples collected from different garden locations

A tablespoon for measuring

A pH color reference chart

A notebook for recording results

Make your indicator solution: chop a head of red cabbage, boil it in water for 20 minutes, and strain the liquid. You'll have a deep purple solution that changes color based on pH. This is real chemistry.

Go outside and collect soil from three to four different spots — under a pine tree, in the vegetable bed, near the compost pile, by the sidewalk. Label each sample.

Place each sample in a separate clear cup. Add a tablespoon of water and stir to create a muddy slurry.

Pour a few tablespoons of cabbage indicator into each cup. Stir gently and watch the color change.

Compare the color against a pH chart: bright pink = very acidic (pH 1-4), light pink = mildly acidic (pH 5-6), purple = neutral (pH 7), blue = mildly alkaline (pH 8-9), green = very alkaline (pH 10+).

Now the gardening science begins. Research which plants prefer which pH. Blueberries love acidic soil (pH 4.5-5.5). Lavender prefers alkaline (pH 7-8). Most vegetables like slightly acidic to neutral (pH 6-7). Plan your planting accordingly.

Soil under pine trees or near oak trees is typically acidic (from decomposing needles and leaves). Soil near concrete or limestone tends to be alkaline. Testing confirms these patterns.

Compare your cabbage juice results to a store-bought soil test kit. They should agree closely.

This experiment naturally raises questions: Can you change soil pH? (Yes — lime raises it, sulfur lowers it.) Why do different areas have different pH? (Parent rock, organic matter, and rainfall all influence it.)

Keep a garden pH map showing different zones. It's useful information for years of planting decisions.