Vinegar isn’t just a condiment to put on your food and use in salads, its acidic makeup actually has a multitude of other uses.
One reason some people use it is to change the color of their hydrangeas.
But how often should you water hydrangeas with white vinegar?
And in fact should you do it at all?
We take a closer look at those questions here.
How Often To Water Hydrangeas With White Vinegar?
Only water your hydrangeas with a dilute solution of white vinegar and water if you have a known pH issue with your soil. Watering alkaline soil with white vinegar regularly over a prolonged period can help achieve a healthy pH level of around 5.5 for your hydrangea. But you need to be extremely careful when doing so. If you are thinking about using vinegar to try and change the color of your hydrangea, don’t! Use a slow-release bluing fertilizer instead.
Soil pH, Vinegar and Hydrangeas – The Basics
As mentioned in our intro, there are gardeners who use vinegar to change the color of their hydrangeas blooms.
But what exactly is the thinking behind this?
Hydrangeas prefer soil that is acidic, although that isn’t to say it is essential as they can be grown in neutral soil, and even handle soil with very slight levels of alkalinity.
But the pH level in the soil does play a part in the colors of the flowers of lacecap and mophead hydrangeas, also known as Hydrangea macrophylla.
- Soil pH of 5.5 or lower: blue flowers
- Soil pH of 5.5 to 6.5: purple flowers
- Soil pH of 6.5 or higher: pink flowers
The thinking is that watering mophead hydrangeas with white vinegar should lower the soil pH and encourage blue flowers to bloom.
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But it isn’t that simple.
It isn’t just the pH of the soil that determines the color of a hydrangeas blooms.
It is also dependent upon the aluminum ions in the soil. The more aluminum ions a hydrangea takes up the bluer the hue of its blooms.
It is a slightly complicated process, but the more acidic the soil the more available these ions are, so the more freely a hydrangea can absorb them.
The problem is though, that soil with a pH that is too low can be toxic and kill plants, even acid-loving ones like hydrangeas.
The same can be said for excessive aluminum in the soil, too much can be dangerous for any plant.
So Is White Vinegar Good for Hydrangeas?
Household vinegar has a pH of 2.4, as anything below 7 is acidic this makes it quite an acidic solution.
However, as we mentioned above it isn’t as simple as applying diluted vinegar to the soil to lower its pH levels.
It can have a number of disadvantages.
Also, note we refer to a dilute solution of vinegar and water, you should never ever consider using concentrate vinegar anywhere around your plants.
It Could Damage the Roots of Your Hydrangea
Vinegar is an active part of organic weed killer, so it obviously can cause damage to plants.
In addition to that hydrangeas have a shallow, tiny and fibrous root system.
Even diluted, vinegar could injure its fragile system.
This could lead to a long-lasting effect on the foliage, and leaves could brown out or die.
It Would Need Application Over a Prolonged Period to be Effective
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For hydrangeas to change color they need a pH change that is sustained over a long time.
Usually, this means more than one growing season.
A heavy rain storm or a wet summer will dilute the soil further and diminish the effects of the vinegar in the soil too.
It Could Deter Beneficial Organisms
The odour of vinegar may encourage unwanted and potentially damaging pests, whilst at the same time deterring beneficial organisms that are good for the soil and your plants.
But It Can Help With Certain Issues
The use of white vinegar can help your hydrangea in some ways, most notably any suffering with signs of chlorosis.
Chlorosis is caused by watering soil using hard water, which has a high lime content. The lime accumulates in the soil, making the pH more alkaline.
As we have already discussed hydrangeas prefer more acidic soil as they can’t absorb the iron they need to flourish properly in alkaline soil.
Usually the first indication that there is a problem is the leaves of the hydrangea turning yellow, and it can eventually kill the plant if no action is taken.
Diluting the irrigation water with vinegar will neutralize the alkalinity and lower the pH of the soil, and help the hydrangeas recover.
How Much Vinegar Should You Put On Hydrangeas?
This is a difficult question to answer as it depends upon a couple of variables.
First of all, you need to carry out a pH test on your soil to see how acidic or alkaline it is.
Then you also need to find out the pH of your tap water if you use that to water your plants. Tap water can vary in pH, and be anything from 6.5 to 8.5. You will be looking to make it slightly more acidic, so somewhere between 6 and 6.5.
If you decide you want to use white vinegar as an acidifier to help chlorotic plants recover, or to change the color of your hydrangeas blooms it is always best to start by erring on the side of caution.
You should be looking to maintain a pH level in your soil of around 5.5.
Most households have alkaline tap water. In these cases, I would suggest starting by mixing one tablespoon of vinegar with a gallon of water.
Make sure you are using normal household white vinegar, which has an acidity ratio of 5%, not horticultural vinegar which has an acidity level of 20%.
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How Often Should You Water Hydrangeas With White Vinegar?
The aim should be to keep the soil around your hydrangea constantly moist.
To determine when to water simply insert your finger to a depth of around 4 inches and then water when it feels dry or almost dry.
When watering with a dilute solution of vinegar make sure you apply it to the soil, not directly to the foliage of the plant.
Keep testing the pH level of your soil and keep an eye on the health of your hydrangea before making any decisions on whether to increase the ratio of water to vinegar and how long to keep watering for.
If you are watering a potted hydrangea you need to be even more careful.
It will have a much more restricted root zone, and the solution of vinegar and water can concentrate in the pot with repeated waterings.
Try cutting the solution down to half a tablespoon of vinegar with a gallon of water.
In my opinion, I would only water your hydrangeas with white vinegar if there is a known pH issue.
Then regular applications of a dilute solution of water and white vinegar can lower the pH of the soil which will help plants recover from chlorosis.
If you are thinking about using white vinegar to try and change the color of your hydrangeas I would say don’t do it.
There are specific fertilizers you can use to turn flowers pink or blue, MiracleGro for Acid Lovers (aka Miracid) is a good one for instance.
Other products like garden sulfur, aluminum sulfate or greensand can also work.
But using vinegar which acts as a herbicide in higher levels, just to try and change the color of your hydrangeas blooms is somewhat of a risk.