Quick Answer
Yes, vinegar can be used to turn hydrangeas blue. Adding aluminum sulfate, which is found in some types of vinegar, lowers the pH of the soil around hydrangeas. This causes the flowers to uptake more aluminum from the soil, turning the blooms a blue or purple color. White vinegar or cider vinegar typically work best.
What Causes Hydrangea Flowers to Turn Blue
Hydrangeas produce blue flowers when grown in more acidic soil with a lower pH, generally between 4.5-5.5. In acidic conditions, hydrangeas are able to uptake aluminum from the soil, which results in blue flowers. Aluminum binds to the anthocyanin pigments in the flowers, changing the color from pink to blue.
If hydrangeas are grown in more alkaline soil with a higher pH above 5.5, they will produce pink flowers. In less acidic conditions, hydrangeas cannot properly uptake aluminum from the soil, so the flowers remain pink.
Therefore, the key to getting blue hydrangea flowers is to lower the pH of the soil by making it more acidic. This allows the plant to absorb aluminum. One easy way to do this is by applying vinegar around the hydrangea’s roots. The acetic acid in vinegar helps lower the pH.
Why Vinegar Works to Change Hydrangea Color
Vinegar contains acetic acid, which lowers the pH of soil, making it more acidic. Most types of vinegars, including white vinegar, apple cider vinegar, and red wine vinegar contain between 4-8% acetic acid.
Adding vinegar to the soil around hydrangeas introduces more acidity, allowing aluminum uptake by the roots. This causes the flowers to turn a blue or purple hue.
Distilled white vinegar or apple cider vinegar work best for changing hydrangea color. Regular, 5% acidity household vinegar provides enough acetic acid to lower the soil pH without harming the plant. Avoid more potent vinegars like 20% acetic acid solutions.
How to Use Vinegar to Turn Hydrangeas Blue
It’s quite simple to use vinegar to alter hydrangea flower color. Follow these steps:
– Test the soil pH around the hydrangeas. Ideal is between 4.5-5.5 pH for blue blooms.
– Obtain white distilled vinegar or apple cider vinegar. Use a 5% acidity solution.
– Mix 1 part vinegar with 3 parts water. This dilutes the acetic acid slightly.
– Apply the diluted vinegar generously around the base of the hydrangea shrubs, about 1-2 cups worth. Focus on soaking the root zone.
– Reapply the vinegar solution every 1-2 weeks during the growing season before the flowers bloom.
– Monitor the soil pH, aiming to keep it between 4.5-5.5. Add more vinegar as needed if pH rises.
– Discontinue vinegar applications once hydrangea flowers turn blue.
When to Apply Vinegar to Hydrangeas
The optimal time to apply vinegar is in early spring, just as the hydrangea leaves begin to emerge. This gives the acetic acid time to thoroughly penetrate the soil around the roots before flowers form.
Continue treating with vinegar every week or two from early spring until the hydrangea blooms, which is typically mid to late summer. The acetic acid will lower the soil pH over time, allowing for aluminum uptake.
Stop adding more vinegar once the hydrangea blooms have shifted to your desired blue or purple shade. Further applications are not necessary after that point.
Where to Apply the Vinegar
It’s important to apply the diluted vinegar solution directly to the soil around the hydrangea roots and avoid getting it on the leaves and stems. Pour or spray the vinegar generously onto the ground around the outer perimeter of the shrub about 6-12 inches from the main stem.
Water the vinegar into the root zone for maximum effectiveness. As the acetic acid leaches down into the soil, it will lower the pH in the rhizosphere where the plant is absorbing minerals. Focus on saturating the area below where the blooms emerge.
Alternative Acidic Soil Amendments Besides Vinegar
While vinegar is an easy, safe way to acidify soil around hydrangeas, there are some other amendments you can use to turn flowers blue as well:
– Aluminum sulfate – introducing more aluminum causes blue blooms. Mix granules into soil.
– Peat moss – made from decayed sphagnum moss, so it’s naturally acidic. Mix with existing soil.
– Coffee grounds – contain acids that lower pH. Sprinkle around plant and till in.
– Composted leaves – as they break down, leaves release tannins and humic acid.
– Elemental sulfur – oxidizes into sulfuric acid. Sprinkle powder onto soil.
– Pine needles – decomposing needles increase acidity. Spread around plant as mulch.
– Vitamin C tablets – contain citric acid. Crush and mix into root zone.
Factors that Impact Hydrangea Color
While soil pH is the main factor controlling hydrangea flower color, there are some other elements that can influence the blooms:
– Variety – some hydrangea species and cultivars are bred to be specific colors.
– Age – older plants may not absorb as much aluminum.
– Climate – cooler regions tend to produce more vivid blue colors.
– Fertilizer – avoid excessive nitrogen which makes soil more alkaline.
– Watering – too much can make soil pH rise. Aim to keep soil moderately moist.
– Sunlight – flowers in shade may appear brighter blue than flowers in sun.
– Soil composition – sandy soils often remain more acidic. Clay soils tend to be less acidic.
– Previous color – plants accustomed to producing pink flowers may not turn blue instantly with acidification.
How Long Does it Take for Vinegar to Change Color?
If your hydrangea blooms are currently pink, it can take some patience for vinegar to change the flowers completely blue. It may require a full growing season or longer to see the color shift.
When vinegar is applied in early spring before blooming, its effects are not instantaneous. The acetic acid takes time to thoroughly permeate the soil and reduce the pH around the roots. Although the flowers may take on a purplish hue the first season of vinegar applications, they likely won’t become vivid blue until the following year.
Continue treating the hydrangeas with regular vinegar applications for 1-2 years. This allows the acidity levels in the soil to drop sufficiently to encourage aluminum uptake and blue pigments. With persistence using vinegar to acidify the soil, your hydrangea flowers will eventually transform into a brilliant sapphire blue.
How to Maintain Blue Hydrangeas
Once your hydrangea flowers have turned blue after acidifying the soil with vinegar, there are some maintenance steps to keep them that vibrant shade in future years:
– Monitor soil pH – test pH 1-2 times per year. Vinegar again if pH creeps above 5.5.
– Mulch annually – place compost, leaves, pine needles or peat around plants. Acidic mulch helps keep pH low.
– Limited nitrogen – avoid excessive nitrogen fertilizer, which can make soil alkaline. Use a low nitrogen, acidic plant food.
– Water carefully – too much water can leach acids from soil. Let soil partially dry between waterings.
– Prune selectively – remove spent blooms but avoid heavy pruning which reduces flower buds.
– Monitor changes – if flowers show signs of pink returning, retest soil and reacidify with vinegar as needed.
– Remove faded blooms – deadheading spent flowers encourages more acid-toned blooms.
– Avoid lime – never apply lime or dolomitic limestone, which raises pH making soil more alkaline.
Potential Issues When Using Vinegar
Vinegar is generally safe for use on hydrangeas when diluted properly, but there are a few potential issues to be aware of:
– Leaf burn – undiluted or very strong vinegar can burn leaves. Always dilute vinegar before applying to soil.
– Root damage – excessive amounts of even diluted vinegar can harm roots. Use caution when pouring onto root zone.
– Plant stress – altering soil pH drastically in short timeframe may impact health. Change pH gradually over time.
– Salt buildup – vinegar breaks down into salts that can accumulate. Flush soil occasionally with hose to avoid excess salts.
– Flower loss – if pH swings drastically up and down, plants may not bloom well. Strive for stable acidity.
– Lack of nutrients – overly acidic soil can limit nutrient availability. Supplement with acidic fertilizer to provide needed minerals.
– Weed growth – vinegar application kills some weeds, but may increase growth of acid-loving weeds like moss over time.
When Not to Use Vinegar on Hydrangeas
Avoid using vinegar in these situations:
– On varieties bred to be pink – vinegar won’t necessarily change their flower color.
– On aluminum-sensitive varieties – it can cause toxicity leading to yellow leaves.
– During a drought – vinegar application without watering can harm roots.
– On new transplants – wait until they are established before altering soil pH.
– On sick plants – vinegar can compound problems for stressed or diseased plants.
– Near other acid-sensitive plants – vinegar could unintentionally change the surrounding soil pH.
– With non-diluted concentrations – high levels of acetic acid act as an herbicide.
– On flowers and leaves – vinegar should only touch the soil to change pH safely.
– With other synthetic acidifiers – combining different pH altering chemicals can harm plants.
– Indiscriminately without testing – monitor soil pH and only apply vinegar when pH is above ideal range.
Conclusion
Vinegar can successfully turn pink hydrangea blooms blue when used properly. Diluted white vinegar or cider vinegar acidifies the soil, which allows hydrangeas to uptake aluminum and produce blue pigments. Apply vinegar around the roots early in the growing season and drench regularly to lower soil pH between 4.5-5.5. Acidifying the soil with vinegar takes patience and persistence to change the color, but it offers an inexpensive, natural method to alter hydrangea flower color over time. Monitor soil pH and continue acidifying as needed to maintain an acidic soil environment for beautiful blue hydrangea blooms.
