Vinegar has a place in the home, but does it belong in the garden? Some gardeners have started using vinegar to lower their soil pHto change bigleaf hydrangea (Hydrangea macrophylla) bloom colors. Does this actually work? The short answer is kind of; in theory, it can. But is it your best long-term solution for altering your soil pH? We don't think so, and here is why!
A Quick Chemistry Lesson
Did you know that hydrangea colors don't directly depend on soil pH for their bloom color? It gets a little more complicated than that! Bloom pigments actually depend on the availability of aluminum ions (Al+) in the soil. In basic soils (pH above 7.5), aluminum ions combine with hydroxide ions (OH-) to form Al(OH)3, which is immobile in the soil and unavailable to plants. However, when the soil acidifies (pH lower than 6.5), these aluminum ions are no longer tied down hydroxide, and can freely mingle with other ions.It will react with other ions, including those plants absorb. This means that aluminum is now "mobile" and can be taken up by plants. As hydrangeas take up more aluminum ions, the blooms take on blue hues. Bigleaf hydrangeas can have blue flowers in acidic soils and pink flowers in basic soils.
While increasing the aluminum mobility in your soil will change your blooms' pigment, it can also be dangerous for your plants! A soil with a pH that is too low can be toxic. An excess of aluminum in the soil can even kill the plant. Make sure you are regularly testing your soil to ensure you are not lowering the pH too much.
What does this have to do with vinegar?
Vinegar is an acidic solution composed of 5% acetic acid and water. A pH of 7 is neutral, and household vinegar has a pH of around 2.4 (which is quite acidic). The theory is, applying diluted vinegar to the soil will lower the pH enough to change the color of your hydrangea blooms. This strategy will make the soil more acidic, but not for long!
Do we think this is a good solution? No, not really. The vinegar will quickly dilute in the soil, especially if it rains or is irrigated, not making much of a pH difference. Plus, for your hydrangeas to change colors, they need a pH change sustained over a long time. It could take even longer than one growing season! Every time you water, you would have to add vinegar to your soil to maintain the pH.
This solution also might not be best for your plant or local wildlife. You may have heard of vinegar being used as a weed killer. The acetic acid in vinegar can easily burn through the wax coating on leaves, destroying any leafy green tissue it's sprayed on. However, the roots aren't harmed by the vinegar when applied directly to the soil. The harsh smell of vinegar will welcome pests like fungus gnats while deterring wildlife from calling your garden home. It even can deter worms and other important soil organisms that are beneficial to your garden!
What are the alternatives?
Personally, we think hydrangea blooms are beautiful in every color and don't recommend altering the pH of your soil. Changing the pH can have some consequences in the garden, including making the soil unsuitable for nearby plants. However, if you're determined to change your bloom color, we'd recommend using garden sulfur or ammonium sulfate to lower the pH, or ground lime to raise the pH. This is easiest in a container, so consider planting your shrub in a large pot!
FAQs
Well, for a quick, cheap and easy fix, you just need apple cider vinegar! Mix one cup of apple cider vinegar with 10 litres of water (an average watering can's worth) and direct the solution at the base of the hydrangea, avoiding the leaves. Do this every couple of weeks and the colour will gradually change.
What color does coffee turn hydrangeas? ›
Some gardeners report success in turning their hydrangeas blue by applying coffee grounds to the soil. The coffee grounds make the soil more acidic, allowing the hydrangea to more easily absorb aluminum.
Can baking soda change hydrangea color? ›
Baking soda is often recommended for hydrangeas for a range of uses, from changing flower color to disease control.
How to turn hydrangeas blue quickly? ›
The easiest way to acidify your soil and turn those babies blue is with aluminum sulfate, which can be found at almost any garden center. Mix ¼ oz aluminum sulfate with a gallon of water and soak the soil surrounding your hydrangeas in the spring, as soon as the plant begins to grow.
Can I use vinegar to make my hydrangea blue? ›
The theory is, applying diluted vinegar to the soil will lower the pH enough to change the color of your hydrangea blooms. This strategy will make the soil more acidic, but not for long!
Does coffee turn hydrangeas blue? ›
If you've been trying to get your hydrangeas to become big and blue, then we might just have the tip for you. Hydrangeas color is based on how acidic your soil is—the more acidic the soil you plant your hydrangeas in, the more blue. We've found that adding a few coffee grounds to your soil can do just the trick.
Do coffee grounds really turn hydrangeas blue? ›
If you're growing hydrangeas, use coffee grounds to affect their color. Coffee grounds add extra acidity to the soil around hydrangeas. On a chemical level, this increased acidity makes it easier for the plant to absorb naturally occurring aluminum in the dirt. The effect is pretty blue clusters of flowers.
What does vinegar do to hydrangeas? ›
Hydrangea flowers will be pink in alkaline soil, but change to blue in acidic soil. So, mix up some apple cider vinegar and water, and give all the acid-loving plants a treat. Or change colors of your hydrangeas on a whim from pink to blue.
How to make hydrangeas purple? ›
Generally speaking, acidic soil, with a pH lower than 6.0, yields blue or lavender-blue hydrangea blooms. Alkaline soil, with a pH above 7.0, promotes pinks and reds. With a pH between 6 and 7, the blooms turn purple or bluish-pink. To lower your pH, add garden sulfur or aluminum sulfate to your soil.
Do tea bags make hydrangeas blue? ›
I turn them a gorgeous shade of blue every year by putting used tea bags in the soil around them," and a third wrote: "Put used broken tea bags around the roots, it will turn a stunning blue colour in no time. Mine turned blue, but preferred the pink so took the tea bags away the blooms went back to pink eventually."
As much as we'd like quick fixes and garden hacks to be true, Epsom salt doesn't offer the results hydrangeas gardeners hope for. It doesn't change the bloom color, promote bigger flowers (unless there is a magnesium deficiency in the soil), or deter pests.
How do I make my hydrangeas deep pink? ›
Measure Soil pH
If you want pink hydrangea flowers, the pH needs to be on the alkaline side. Finding the pH of your soil is quick and easy to do with a soil test kit. A reading above 7.0 means that your hydrangeas should produce pink flowers without you having to do anything else.
How much apple cider vinegar to change hydrangea color? ›
Well, for a quick, cheap and easy fix, you just need apple cider vinegar! Mix one cup of apple cider vinegar with 10 litres of water (an average watering can's worth) and direct the solution at the base of the hydrangea, avoiding the leaves. Do this every couple of weeks and the colour will gradually change.
Does Epsom salt change the color of hydrangeas? ›
Unless your soil is deficient in magnesium (or inhibits the uptake of magnesium), Epsom salt is bad for hydrangeas. It does not change soil pH and, by extension, flower color, or improve flowering without deficiencies present.
