pH Indicator Definition and Examples

Home and Garden pH Indicators

By Anne Marie Helmenstine, Ph.D.

Updated September 16, 2019

There are many common household products and garden plants that can be used as pH indicators. Most plants contain pH-sensitive anthocyanins, making them perfect for testing acid and base levels. Many of these natural pH indicators exhibit a broad range of colors.

Plants You Can Use to Test pH Levels

The natural world has given us numerous plants, from beets to grapes to onions, that can be used to test the pH levels of a solution. These natural pH indicators include:

Beets: A very basic solution (high pH) will change the color of beets or beet juice from red to purple.

Blackberries: Blackberries, black currants, and black raspberries change from red in an acidic environment to blue or violet in a basic environment.

Blueberries: Blueberries are blue around pH 2.8-3.2, but turn red as the solution becomes even more acidic.

Cherries: Cherries and their juice are red in an acidic solution, but they turn blue to purple in a basic solution.

Curry Powder: Curry contains the pigment curcumin, which changes from yellow at pH 7.4 to red at pH 8.6.

 Delphinium Petals: The anthocyanin delphinidin changes from bluish-red in an acidic solution to violet-blue in a basic solution.

Geranium Petals: Geraniums contain the anthocyanin pelargonidin, which changes from orange-red in an acidic solution to blue in a basic solution.

Grapes: Red and purple grapes contain multiple anthocyanins. Blue grapes contain a monoglucoside of malvidin, which changes from deep red in an acidic solution to violet in a basic solution.

Horse Chestnut Leaves: Soak horse chestnut leaves in alcohol to extract the fluorescent dye esculin. Esculin is colorless at pH 1.5 but becomes fluorescent blue at pH 2. Get the best effect by shining a black light on the indicator.

Morning Glories: Morning glories contain a pigment known as "heavenly blue anthocyanin," which changes from purplish-red at pH 6.6 to blue at pH 7.7.

Onion: Onions are olfactory indicators. You don't smell onions in strongly basic solutions. Red onion also changes from pale red in an acidic solution to green in a basic solution.

Petunia Petals: The anthocyanin petunin changes from reddish-purple in an acidic solution to violet in a basic solution.

Poison Primrose: Primula sinensis has orange or blue flowers. The orange flowers contain a mixture of pelargonins. The blue flowers contain malvin, which turns from red to purple as a solution goes from acidic to basic.

Purple Peonies: Peonin changes from reddish-purple or magenta in an acidic solution to deep purple in a basic solution.

Red (Purple) Cabbage: Red cabbage contains a mixture of pigments used to indicate a wide pH range.

Rose Petals: The oxonium salt of cyanin turns from red to blue in a basic solution.

Turmeric: This spice contains a yellow pigment, curcumin, which changes from yellow at pH 7.4 to red at pH 8.6.

Household Chemicals That Are pH Indicators

If you don't have any of the materials above at hand, you can also use some common household chemicals to test pH levels. These include:

Baking Soda: Baking soda will fizz when added to an acidic solution such as vinegar, but will not fizz in an alkaline solution. The reaction doesn't readily reverse itself, so while baking soda can be used to test a solution, it can't be reused.

Color-Changing Lipstick: You'll need to test your color-changing lipstick to determine its pH range, but most cosmetics that change color respond to changes in pH (these are different from cosmetics that change color according to the angle of light).

ExLax Tablets: These tablets contain phenolphthalein, which is a pH indicator that is colorless in solutions more acidic than pH 8.3 and pink to deep red in solutions more basic than pH 9.

Vanilla Extract: Vanilla extract is an olfactory indicator. You can't smell the characteristic scent at high pHs because the molecule is in its ionic form.

Washing Soda: As with baking soda, washing soda fizzes in an acidic solution but not in a basic solution.