The full blossoms of hydrangea shrubs are an absolute show-stopper in the garden. It’s no wonder they’re still an old-fashioned favorite. As someone with a degree in landscape architecture, I’ve always appreciated the eye-catching balls of blossoms, especially when the colors are vibrant.
But there’s something truly special Hydrangea macrophylla — the blossoms can change color depending on the soil.
Gardeners first noticed this anomaly back in the 18th century, and they experimented with changing hydrangea colors by pouring tea on the plants, burying rusty nails and coffee grounds in the soil, and even chanting spells.
But it wasn’t magic that changed the color of the hydrangea flowers.
It was the soil pH. Specifically, whether or not the hydrangeas were absorbing aluminum from the soil.
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6 Facts to Know Before You Try to Change Hydrangea Color
Sounds like a simple solution — if you want to change the color of your hydrangea flowers, just change the pH of the soil.
But there’s a little more to it than that.
Here’s what you need to know before you start playing with the soil conditions of your hydrangeas:
- Even if the soil conditions are correct, not all varieties of hydrangeas will pick up aluminum from the soil effectively enough to change the blossom color. If you want a blue hydrangea, your safest bet is to start with a blue variety from your local nursery.
- White hydrangeas seem like they should be a blank canvas, but unfortunately, they will stay white regardless of the soil. The blossoms might adopt a greenish hue as they age, but they aren’t going to turn blue, pink, or purple.
- Turning a blue hydrangea pink is harder than turning a pink hydrangea blue.
- It’s not a one-and-done annual soil treatment. You’ll need to treat the soil 1-3 times a year (depending on your climate and growing season) in order to achieve results.
- The soil is easier to control if the hydrangea is potted in a container.
- The intensity of the hue, whether you’re trying to change your hydrangea color to pink, blue, or purple, is going to largely depend on the variety of hydrangea you have. Some varieties will adopt a deep, rich color, but others will be a pale hue no matter how much you change the soil conditions. (Tip: Hydrangea macrophylla ‘Mathilda Gutges’ is a GREAT variety to buy if you want a deep pink or intense blue in your garden.)
Hydrangeas, like azaleas and rhododendrons, prefer soil that is more acidic than alkaline to start with.
Before you start adjusting the soil acidity, you should consider purchasing a simple soil pH test kit or a soil pH meter so you know what type of soil you’re starting out with.
Acidic soils will have a pH below 6.
Alkaline soils will have a pH above 6, and they often contain clay.
Make sure your plants are in good health if you want them to put on a show in the summer and fall with large, colorful blooms. If you notice your plant isn’t looking healthy (wilting, brown edges on the leaves, sparse foliage), stop putting additives in the soil and focus on making the hydrangea happy first, especially if it’s been recently planted and needs to establish itself.
Hydrangeas do like sun, but too much can scorch the leaves, and they’re not drought tolerant. I live in the Midwest and prefer to grow mine in light shade so they don’t get fried in the summer heat. Pay attention to your hydrangea’s needs — they’re quick to let you know when they’re thirsty, but they’re also quick to perk back up after a drink.
How to Change Hydrangea Color to Pink
Pink hydrangea blossoms indicate that the plant is absorbing aluminum from the soil. In order to turn (or keep) hydrangeas pink or red, the shrub will need alkaline soil.
Working garden lime into the soil until you’ve achieved a pH of at least 7.0 will give you the proper soil conditions needed to change your hydrangea color to pink.
Pay close attention to the health of your hydrangea and be cautious about how much / how often you add the garden lime so you don’t damage the roots.
How to Change Hydrangea Color to Blue
When a hydrangea isn’t taking in aluminum, the blossoms will be blue or lavender-blue. In order to achieve blue hydrangea flowers, the soil needs to be acidic.
You can add garden sulfur or aluminum sulfate to acidify the soil below 6.0 pH. Aim for a 5.0 pH or a little lower for maximum blue color.
If you have hard water, try to collect and use rainwater instead when you water your hydrangea. You’ll likely need to use the soil acidifier several times during the growing season to maintain blue hydrangea flowers. Read the instructions carefully to make sure you don’t use too much and burn the roots.
Remember, some hydrangea varieties won’t turn blue, even if the soil is acidic. Others may respond but stay more of a lavender or pale blue despite your best efforts.
How to Change Hydrangea Color to Purple
Purple hydrangea blossoms walk the line between pink and blue, alkaline and acidic. The optimal pH for changing hydrangea color purple is between 6.0 and 7.0.
Ideally, you should test the soil’s pH so you know what adjustments to make.
If your hydrangea flowers are too blue for your taste, work a little garden lime into the soil to make it more alkaline. If your hydrangea flowers are too pink, add some garden sulfur or aluminum sulfate into the soil to make it more acidic.
Transform Your Garden by Experimenting with Hydrangeas
Changing hydrangea colors is a fun way to push the limits of your garden. It’ll take some trial and error to get the color you want.
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If your hydrangeas aren’t responding to your efforts by the end of the growing season, you probably have a variety that isn’t receptive to soil changes. You can simply love them as they are, or take a trip out to your local plant nursery to find a different variety to plant.
Best of luck, and happy gardening!
Award-winning fantasy author, freelance writer, spiritual explorer, and sole founder of Green Witch Lunar Witch. She created her first website in 2016 and published her first novel two years later. Sara spends most of her time writing, creating, and daydreaming.