Have you ever had a blue hydrangea turn pink? Here are some things you need to know on how to keep or change the color of your hydrangeas.
Hydrangea flowers dress to impress and put on quite the summer/fall show when in full bloom. Many gardeners favor hydrangeas and they’re certainly a cottage garden staple. These fast-growing shrubs have large flowers in a wide range of forms, types, and colors. One flower practically makes a whole bouquet!
A reader emailed me asking why her gorgeous blue mophead hydrangea was turning pink one year after she planted it. This was happening with my client’s Endless Summer Hydrangeas so I knew the answer.
Why Do Hydrangeas Change Color?
First off, hydrangeas prefer and do best in soil on the acid side just like rhododendrons, azaleas, Japanese maples, pieris, etc. The change in the color of your hydrangea is due to the pH of your soil. Soil runs from acidic to alkaline with varying degrees in between.
The health of your plants is dependent on the health of your soil. In regards to hydrangeas, the flower color is affected and determined by the soil pH.
If your soil is more alkaline, then your hydrangeas will be pink or pinker. Alkaline soils, with a pH approximately from 7 – 9, generally contain clay. If your soil is more acidic, pH around or less than 5.5, then your blue hydrangeas stay blue or bluer.
If you know your soil is more on the alkaline side, you want to apply the garden sulfur or soil acidifier upon planting blue hydrangeas. Aren’t sure? If you’re unsure of your soil’s pH, you can find a soil lab in your state or buy a simple soil pH test kit or pH meter online.
5 Important Things To Know
It’s best to start the color changing or color keeping treatment right when you plant a blue hydrangea.
1 application doesn’t do it. You want to apply a soil acidifier 2-3 times a year. In climates with warmer winters and a longer growing season, 3 applications is optimum.
Turning a pink hydrangea blue is easier than turning a blue hydrangea pink.
You would think that white hydrangeas (including Pee Gee and Oakleaf), being like a blank canvas, would be easy to turn blue. Not so and don’t bother trying. They’re unaffected by soil pH.
I find it easiest to control the soil pH with container planted hydrangeas. More on this below.
How to Make or Keep Hydrangeas Blue in Color
Some ask if coffee grounds, epsom salt, rusty nails, or vinegar can change hydrangea color. I’ve never tried any of these but the truth is, you have to focus on the soil.
I changed the color of my client’s Endless Summer Hydrangea back to blue with a soil acidifier. This product is organic and derived from elemental sulfur and gypsum.
I worked it into the soil, to a depth of around 4”, in a circle halfway between the drip line and the base of the plant.
Be sure to follow the directions and use the recommended amount for the size of your hydrangea. You don’t want to overdo it hoping to get a deep blue hydrangea. Even though this is an organic element, you can easily overdo it.
Make sure the soil is moist when you apply the acidifier and water it in well when you’re done. The water which works it in and makes it effective. If your garden isn’t on drip or you don’t get consistent summer rains, then water with the hose or a watering can.
A 2 – 3” layer of compost around the root ball will add nourishment and help to conserve moisture. Hydrangeas aren’t drought-tolerant plants so you should be watering them anyway!
Applying this is a slow process when it comes to changing the color – don’t expect immediate results. However, the results are long-lasting but it will need to be applied in subsequent years to keep the color blue(ish). It’s not a 1 season deal and your hydrangea stays blue.
I did this 3 times a year in temperate coastal California because the hydrangeas have a long bloom time here. If you’re in a cold climate, you may only have to do it 2 times a year.
Have you ever wondered why florist hydrangeas have such vibrant, deep colors and yours in the garden don’t? It’s because the growers make alterations to the soil mix right from the get-go and throughout the growing process. Plus, these small plants are bred to have big blooms.
Hydrangeas In Containers
It’s much easier to change or keep the color of hydrangeas in containers than it is in the garden. This is because you can plant them in a planting mix formulated for acid-loving plants so the soil pH is lower, to begin with.
And, because the soil is looser than it would be in the garden, it’s much easier to apply the soil acidifier. You may only have to do it once or twice a year.
When I started applying garden sulphur to my client’s endless summer hydrangea, it took all season for the flowers to start to turn blue. After 3 applications, the flowers were turning a pale bluish/lavender in September.
It depends on the sun & the amount of heat.
Most hydrangeas do best in full sun up to noon or 1, especially if you live in a climate with a good amount of summer sun. Hot afternoon sun will burn a hydrangea in no time. I live in Tucson, Arizona so I wouldn’t even think of trying a hydrangea here not only because of the heat & sun, but because of the water issue.
The client I refer to in this post lives just south of San Francisco, 6 blocks from the Pacific Ocean. This is a cooler area with quite a bit of fog. Most of her many hydrangeas grow in full sun & do great. We had hydrangeas growing on our property in Connecticut & they did fine in full sun also.
The flowers opening up after the soil acidifier had been applied a few times.
Yes you should. I always did because the plant looks better. Some people leave them on for the winter & prune them off in spring.
I never fertilized hydrangeas when I was a professional gardener. They grew healthy, looked just fine & bloomed away (although some years heavier than others).
I would apply a good layer of compost from local landscape supply companies every year or 2. It not only nourished the plants but helped to conserve moisture.
I’m a big proponent of working with the soil you have and planting plants appropriate for that soil type. That being said, if you must have blue hydrangeas and your soil is on the alkaline side, have at it with the garden sulfur or another soil acidifier.
You may well get some lavender/blue flowers on your hydrangea. The colors can vary, that’s for sure.
You may never get your hydrangeas back to that intense blue they were or that you want them to be. In the case of my client’s hydrangea, the flowers turned pale blue and lavender blue (see the picture directly below).
May your garden stay blue(ish)!
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