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Baking Soda or Coffee Grounds for Blue Hydrangeas: Fact or Fiction?

Many gardeners are fascinated by the chameleon-like qualities of hydrangeas, particularly their ability to shift bloom colors from pink to blue. This change is often attributed to soil pH, leading to a common question: can household remedies like baking soda or coffee grounds effectively alter soil pH for these beautiful shrubs?

We asked our National Garden Bureau expert members for their take, and here’s what they had to say:

1. Can Baking Soda Change Your Soil pH for Hydrangeas?

Proven Winners Color Choice: “No.”

“First of all, baking soda is a base, so even if it were effective, it would actually make your soil more alkaline. This is the opposite of what most people are trying to accomplish by changing their soil pH for hydrangeas, which is to turn bigleaf hydrangea ( H. macrophylla) from pink to purple/blue. For a hydrangea to undergo that color change, two things must be true: the soil must contain aluminum, which is what actually affects the change, and it must be acidic. Only in acidic conditions are the aluminum ions free from their bonds so the plant can take them up and metabolize them.

Since adding baking soda would actually make the soil more alkaline – if it were effective in the first place, which it isn’t, at least not in any realistic quantity – it would prevent the hydrangea from turning blue. While it is true that in some areas, soil is naturally so acidic, or can become so acidic, that it is not favorable for plant growth, if you were trying to raise the pH of your soil, baking soda would not be the best way to do it from an efficacy or price standpoint. What’s the point of a short-lived soil pH change?”

2. Can coffee grounds effectively change the pH of your soil?

Southern Living® Plant Collection: “No.”

“Unused coffee grounds are highly acidic and aren’t generally recommended to use directly on plants in the garden. Spent coffee grounds have a neutral pH. The safest way to use coffee grounds in the garden is to add spent coffee grounds to your compost and use the compost around your plants once it has matured.”

3. Realistically, can you change the soil pH enough to impact the color of your hydrangea blooms using these "Homemade" methods?

Proven Winners Color Choice: “No.”

“If someone is trying to change the color of their hydrangea, we recommend the following:

1. First, you need to have a hydrangea that can change color in the first place. This means it must be one of three types: a big leaf, a mountain hydrangea, or Fairytrail Fresco Cascade Hydrangea. It also must be a pink/purple/blue variety, as white and green hydrangeas of these species will not change color.
2. Ideally, you should get a soil test, so you know whether your soil needs a pH change or aluminum or both, since the soil must be both acidic and contain aluminum to change the flower color. The majority of products on the market are merely soil acidifiers, so if the issue is that your soil doesn’t contain aluminum, such products would acidify your soil without ever changing the flower color. Aluminum is naturally occurring in many soils, but tends to be highest in clay soils over sandy ones.
3. You will always get the best results by using a product made for the purpose and following the package directions carefully.”

Southern Living® Plant Collection: “No”

“These methods may ultimately harm your plants and the health of the soil. There is no quick fix for changing the color of hydrangeas, and the effects of adjusting the soil pH may take months to produce a noticeable change; it often requires one or two growing seasons.”

4. Does baking soda play any important and beneficial role in other areas of your garden?

Southern Living® Plant Collection: "No"

Baking soda is not recommended for use on plants in the garden, as it is a type of salt and can be toxic to plants if overused. However, it can help remove rust on tools when mixed into a paste.

So the best way to change the color of a hydrangea is by:

Having a soil test to see the pH of your soil. Bring in a cup of soil to Wedel's Plant Doctors for a free pH test.

Use proper ingredients that are made for this purpose. Wedel’s Plant Doctors will prescribe either Hi-Yield Soil Sulfur to turn your hydrangeas blue or Espoma Garden Lime to turn your hydrangeas pink.

Article by National Garden Bureau with edits from Wedel's