How To Make Hydrangeas Blue With Pennies

Pennies contain copper, which can slightly acidify soil and shift hydrangea blooms toward blue. If you’ve been searching for how to make hydrangeas blue with pennies, you likely have a pink or purple shrub that just won’t cooperate. This old gardener’s trick is cheap, simple, and surprisingly fun to try.

But here’s the honest truth: pennies alone are not a magic wand. They work best when combined with a few other soil adjustments. Let’s break down exactly what copper does, why your hydrangeas are pink, and how to give those pennies a fighting chance.

The science is straightforward. Hydrangea color depends on soil pH and the availability of aluminum ions. Pink blooms mean your soil is too alkaline (pH above 6.5) or lacks aluminum. Blue blooms require acidic soil (pH below 5.5) with soluble aluminum present.

Copper from pennies does not directly turn flowers blue. Instead, copper can help lower soil pH slightly, which in turn makes aluminum more available to the plant. Think of pennies as a gentle nudge, not a bulldozer.

Why Copper Helps Acidify Soil

When copper oxidizes in moist soil, it releases copper ions. These ions can displace other minerals and contribute to a lower pH reading. However, the effect is slow and localized. You won’t see a dramatic change overnight.

For pennies to work, they must be placed near the root zone, not just scattered on top of the soil. The roots need to absorb the copper and the surrounding soil needs to become more acidic over time.

What Kind Of Pennies To Use

Not all pennies are created equal. Pennies minted before 1982 are 95% copper. Those minted after 1982 are 97.5% zinc with a thin copper plating. The older pennies are more effective because they contain more copper.

Check the date on your coins. If you have a jar of old pennies from the 1970s or earlier, those are your best bet. Newer pennies still work, but they degrade faster and release less copper.

Step-By-Step Guide To Using Pennies

Follow these steps to give your hydrangeas the best chance of turning blue. Remember, this is a slow process that requires patience.

Test your soil pH first. You can buy a cheap test kit online or at a garden center. If your pH is above 6.5, you need to lower it significantly. Pennies alone won’t do that.
Scratch the pennies. Use sandpaper or a file to rough up the surface. This exposes more copper to the soil and speeds up oxidation. Clean pennies are less effective.
Dig small holes around the drip line. The drip line is where the outermost branches end. Dig 3-4 holes, about 4 inches deep, evenly spaced around the shrub.
Drop 5-10 pennies in each hole. Bury them and cover with soil. Do not place them directly against the main stem.
Water deeply. Moisture is essential for copper to leach into the soil. Water the entire root zone thoroughly after burying the pennies.
Repeat every 3-4 months. The copper will slowly dissolve. Reapply to maintain the effect, especially during the growing season.

Why Pennies Might Not Be Enough

Here is where many gardeners get frustrated. They bury a dozen pennies, wait a year, and still see pink flowers. The reason is simple: copper’s effect on pH is minimal compared to other soil amendments.

If your soil is heavily alkaline (pH 7.5 or higher), pennies will not fix the problem. You need a more aggressive approach. Think of pennies as a supplement, not a primary treatment.

Combining Pennies With Other Methods

To actually see blue blooms, you must address both pH and aluminum levels. Here are the most effective ways to do that, used alongside your pennies.

Lower Soil pH With Sulfur

Elemental sulfur is the gold standard for acidifying soil. It works slowly but reliably. Apply it in early spring or fall according to package instructions. The sulfur bacteria in the soil convert it to sulfuric acid, which lowers pH.

Apply 1/2 cup of sulfur per 10 square feet for a slight pH drop.
For a bigger drop, use 1 cup per 10 square feet.
Water it in well after application.

Add Aluminum Sulfate

This is the quickest fix. Aluminum sulfate both acidifies the soil and adds soluble aluminum directly. It’s the most reliable way to turn hydrangeas blue, but it must be used carefully.

Dissolve 1 tablespoon of aluminum sulfate in 1 gallon of water.
Pour this solution around the base of the plant in early spring.
Repeat every 2-3 weeks during the growing season.
Do not overdo it, as too much can burn the roots.

Use Coffee Grounds And Pine Needles

Organic matter can help maintain acidity over time. Coffee grounds are mildly acidic and add nitrogen. Pine needles are excellent mulch for acid-loving plants. Both work well with your buried pennies.

Spread a 1-inch layer of coffee grounds around the base.
Mulch with 2-3 inches of pine needles.
Reapply these every few months as they decompose.

How Long Until Blooms Turn Blue

Do not expect instant results. Hydrangeas set their flower buds in late summer for the following year. If you start now, you may see a color shift in the next blooming cycle, not the current one.

Typically, it takes 6-12 months to see a noticeable change. The flowers may first turn a muddy purple or mauve before becoming blue. That is a good sign that the pH is dropping.

Common Mistakes To Avoid

Many people try this trick and fail because of simple errors. Here is what not to do.

Do not place pennies on top of the soil. They will oxidize but the copper won’t reach the roots effectively.
Do not use pennies on potted hydrangeas. The confined soil volume makes copper toxicity more likely.
Do not expect results in alkaline clay soil. You must amend the soil aggressively first.
Do not combine pennies with lime. Lime raises pH and cancels out your efforts.

Which Hydrangea Varieties Respond Best

Not all hydrangeas can turn blue. Bigleaf hydrangeas (Hydrangea macrophylla) are the classic color changers. They respond strongly to soil pH. Mountain hydrangeas (Hydrangea serrata) also respond well.

White hydrangeas, oakleaf hydrangeas, and panicle hydrangeas do not change color based on soil pH. They stay white or cream regardless of what you do. Do not waste your pennies on these.

Testing Your Soil After Treatment

You should retest your soil every few months to monitor progress. This tells you if your efforts are working or if you need to adjust your approach. Aim for a pH between 5.0 and 5.5 for the bluest blooms.

If the pH is still above 6.0 after several months, increase your sulfur application. If it drops below 5.0, ease off, as the soil may become too acidic for the plant’s health.

Alternative Copper Sources

If you don’t have enough old pennies, you can use other copper-rich materials. Copper wire, copper pipe scraps, or even copper fungicides can provide the same effect. Just bury them near the roots like you would with pennies.

Some gardeners swear by placing a few copper nails in the soil. These release copper slowly and are easier to find than pre-1982 pennies. The principle is exactly the same.

Maintaining Blue Blooms Year After Year

Once your hydrangeas turn blue, the work isn’t over. Soil pH naturally drifts back toward its original level over time. You must keep up with your amendments to maintain the color.

Reapply sulfur or aluminum sulfate every spring.
Keep mulching with pine needles.
Bury fresh pennies every 6 months.
Monitor pH twice a year.

Frequently Asked Questions

Do pennies really turn hydrangeas blue?
Pennies can help by adding copper to the soil, which slightly lowers pH. However, they are rarely enough on their own. You usually need sulfur or aluminum sulfate for a reliable color change.

How many pennies do I need per hydrangea?
Use about 20-40 pennies per mature shrub. Bury them in clusters of 5-10 around the root zone. More is not better, as excessive copper can harm the plant.

Can I use any copper coin?
Old pennies (pre-1982) are best because they are mostly copper. Newer pennies are mostly zinc. Copper wire or small copper pipe pieces work just as well.

How long does it take for pennies to work?
You may see a slight color shift in 6-12 months. Full blue blooms may take up to two growing seasons, especially if your soil is very alkaline.

Will pennies hurt my hydrangea?
In normal amounts, pennies are safe. Too much copper can be toxic, so stick to the recommended number. Never place pennies directly against the main stem or roots.

Final Thoughts On The Penny Trick

Using pennies is a fun, low-cost experiment that can contribute to blue hydrangeas. But it works best as part of a broader soil management plan. Test your soil, amend with sulfur or aluminum sulfate, and use pennies as a supplemental boost.

Patience is your best tool here. Hydrangeas are slow to respond to soil changes, but when they finally shift from pink to blue, the wait feels worth it. Keep your soil acidic, keep those old pennies buried, and enjoy the show.

Remember, the exact keyword how to make hydrangeas blue with pennies is a starting point, not a complete solution. Combine it with proper soil care, and you’ll have the blue blooms you’ve been dreaming of. Just don’t forget to water, mulch, and test your soil regularly. Happy gardening.