If you’re wondering how to make hydrangeas blue with pennies, you’ve likely heard this classic garden hack. The old gardening tip about using pennies to turn hydrangeas blue is rooted in a scientific principle, though modern methods may be more reliable. This article will explain the penny method, the science behind it, and give you practical steps to try it yourself.
We’ll also cover more effective ways to manage your soil’s pH for those stunning blue blooms. Understanding why this works is the first step to becoming a hydrangea color expert.
How To Make Hydrangeas Blue With Pennies
The idea behind using pennies is simple. It relies on the copper content in pre-1982 pennies. As the penny corrodes in the soil, it releases tiny amounts of copper. This copper can theoretically lower the soil pH, making it more acidic.
Acidic soil is the key to blue hydrangea blooms. In acidic conditions, aluminum in the soil becomes available for the plant to absorb. This aluminum reacts with pigments in the flowers, creating that iconic blue color.
It’s a charming idea that connects gardening to history and chemistry. However, the amount of copper released is very small and slow. For gardeners with neutral or alkaline soil, pennies alone are rarely enough to cause a significant color change.
The Science Of Hydrangea Color
Not all hydrangeas can change color. This magic only happens with bigleaf hydrangeas, specifically Hydrangea macrophylla. These are the classic mophead and lacecap varieties. Their flower color is directly influenced by soil pH and the presence of aluminum.
Here is the basic color guide based on soil conditions:
- Blue Flowers: Occur in acidic soil (pH below 6.0). Aluminum is available and taken up by the plant.
- Pink Flowers: Occur in alkaline to neutral soil (pH above 7.0). Aluminum is locked up and unavailable.
- Purple Flowers: A mix of both, often found in slightly acidic to neutral soil (pH around 6.0 to 6.5).
White hydrangeas, like the popular ‘Annabelle’ type, are not affected by soil pH. Their color is genetically set to white or green.
What You Need For The Penny Method
Gathering your supplies is easy. You likely have most of them at home already. Here is what you’ll need to try the traditional penny method.
- Pre-1982 U.S. Pennies: These are essential. Pennies minted before 1982 are 95% copper. After 1982, they are mostly zinc with a thin copper plating, which won’t work as well.
- A Small Trowel or Digging Tool: For burying the pennies around the plant’s root zone.
- Watering Can or Hose: To water the area after applying the pennies.
- Vinegar (Optional): Some gardeners add a cup of white vinegar to a gallon of water to boost acidity when watering.
Before you start, it’s wise to test your soil pH. You can buy an inexpensive test kit from any garden center. This tells you your starting point and how much change you need to aim for.
Identifying the Right Hydrangeas
First, confirm you have a bigleaf hydrangea. Look for these features: broad, glossy leaves and large, round flower clusters (mophead) or flat clusters with tiny center flowers surrounded by larger ones (lacecap). If your hydrangea has always been white, it will not turn blue.
Finding Pre-1982 Pennies
Check your coin jar or ask friends and family. You can also visit a local bank and ask for rolls of pennies to sort through. You’ll need about 20-30 old pennies for one established shrub. The older and more worn they are, the better they may corrode.
Step-by-Step Guide To Using Pennies
Follow these steps to apply the penny method to your hydrangeas. The best time to start is in early spring, as the plant begins its active growth.
- Test Your Soil pH: Use a home test kit. This gives you a baseline. If your soil is very alkaline (pH above 7.5), the penny method will likely need supplementation.
- Prepare the Area: Remove any thick mulch from around the base of the hydrangea. You want the soil exposed in a circle extending out to the drip line (where the branches end).
- Bury the Pennies: Use your trowel to dig small holes, 2-4 inches deep, around the root zone. Space them evenly. Place 2-3 pennies in each hole and cover them with soil.
- Water Thoroughly: Soak the area well. If using the vinegar mixture, apply it now. The moisture helps start the slow corrosion process.
- Reapply and Monitor: Add a few more pennies every 4-6 weeks during the growing season. Observe the color of new blooms. The change, if it occurs, will be gradual over one or two seasons.
Remember, patience is key. This is a slow, folk method. Don’t expect overnight miracles from a few cents buried in the ground.
More Reliable Methods For Blue Hydrangeas
For more consistent and faster results, most gardeners use targeted soil amendments. These methods directly adjust soil pH and add aluminum.
Using Aluminum Sulfate
Aluminum sulfate is the most effective product for turning hydrangeas blue. It both acidifies the soil and adds the necessary aluminum. Follow package instructions carefully, as too much can harm plant roots.
A typical application involves dissolving 1 tablespoon of aluminum sulfate in a gallon of water. Apply this to the soil around the plant in early spring, avoiding getting it on the leaves. Repeat every 2-4 weeks during the growing season, but stop once buds begin to show color.
Using Elemental Sulfur or Soil Acidifiers
Elemental sulfur is a slow-acting but long-lasting soil acidifier. It works by encouraging soil bacteria to produce acid. It’s best applied in fall, as it takes months to change pH.
Granular soil acidifiers, often made from sulfur and iron, are available at garden stores. They are easy to apply according to the label directions based on your soil type and current pH.
Choosing the Right Fertilizer
Fertilizer plays a big role. To encourage blue flowers, use a fertilizer that is low in phosphorus. High phosphorus levels (the middle number in N-P-K) can bind aluminum in the soil, making it unavailable.
Look for a fertilizer labeled for acid-loving plants, like azaleas or rhododendrons. These typically have a formulation that supports lower soil pH. A slow-release fertilizer applied in spring is often the best choice.
Common Mistakes And How To Avoid Them
Even with good intentions, it’s easy to make errors when trying to change hydrangea color. Here are common pitfalls and how to steer clear.
- Not Testing Soil First: Applying amendments blindly can stress the plant. Always test your pH first.
- Using Post-1982 Pennies: Modern pennies won’t provide enough copper. Make sure you have the older ones.
- Over-Applying Amendments: More is not better. Excessive aluminum sulfate or sulfur can burn roots and damage the plant. Follow rates on the package.
- Expecting Instant Results: Color change happens on new growth. You may not see a significant shift until the next flowering cycle.
- Watering with Hard Water: Tap water that is high in lime (alkaline) can slowly raise your soil pH, counteracting your efforts. Use rainwater when possible for watering your hydrangeas.
Avoiding these mistakes will save you time and keep your hydrangeas healthy through the process. Consistency is more important than intensity.
Maintaining Blue Blooms Year After Year
Once you achieve those beautiful blue flowers, you’ll want to keep them. Maintenance is simpler than the initial change, but it requires regular attention.
Test your soil pH annually, preferably in early spring. If the pH begins to creep above 6.0, apply a maintenance dose of your chosen acidifier. A single application of aluminum sulfate or an acid-loving plant fertilizer in spring is often sufficient.
Continue to use low-phosphorus fertilizer. Mulch around the plant with organic matter like pine needles or oak leaves, which break down and help maintain slight acidity. Collecting and using rainwater for irrigation is one of the best long-term practices for sustaining blue blooms.
FAQ Section
Here are answers to some frequently asked questions about changing hydrangea color.
Can I Use Other Copper Items Instead of Pennies?
Some gardeners experiment with copper piping scraps or copper wire. The principle is the same, but surface area and corrosion rates differ. Pennies are a convenient, small-dose option. Larger copper pieces are not recommended as they could potentially release too much copper too quickly, which can be toxic to soil life in high concentrations.
How Long Does the Penny Method Take to Work?
If it works, you might see a slight shift toward purple or blue hues in the same season, but a full, vibrant blue often takes a full year or more. The change is very gradual because the copper release is minimal. For quicker results, combine pennies with other acidifying methods.
Will Pennies Harm My Soil or Plants?
In the small quantities used for this hack, pre-1982 pennies are generally considered safe. The copper release is very slow. However, in very large quantities, copper can accumulate and become toxic to earthworms and microorganisms. Stick to the recommended amount of 20-30 pennies per shrub.
Why Are My Hydrangeas Still Pink After Trying Everything?
If your soil is naturally very alkaline or contains a lot of limestone, it has a high “buffering capacity.” This means it resists pH change. In such cases, growing hydrangeas in containers where you can completely control the soil mix might be the most reliable way to get blue flowers. Also, double-check that you have a color-changing variety.
Is It Easier to Keep Blue Hydrangeas Blue or Change Pink Ones?
It is generally easier to maintain a blue hydrangea than to change a pink one to blue. If you purchase a hydrangea that is already blue, it’s a sign it’s growing in acidic conditions. Your main job is to maintain that acidity with annual amendments and proper watering.
In conclusion, the method of how to make hydrangeas blue with pennies is a fascinating piece of gardening folklore with a basis in science. While it may not be the most potent or fast-acting solution, especially in challenging soils, it’s a fun experiment that connects us to past generations of gardeners. For more assured results, combining the penny method with targeted soil acidifiers and aluminum sulfate is a smart strategy. The most important steps are always to know your soil pH, confirm you have the right type of hydrangea, and be patient. With consistent care, you can influence your garden’s palette and enjoy the serene beauty of blue hydrangeas.