One of the most interesting aspects of growing Bigleaf hydrangeas is the ability to change their color. It isn't easy and it doesn't happen overnight, but if the beautiful pink or blue hydrangea you brought home from the nursery has started to look a little muddy and pale, you can restore its color (or change it) by adjusting the pH of your soil.
The pH scale runs from 1.0 (strongly acid) to 14.0 (strongly alkaline), 7 being neutral. In general, plants grow best in soil with a pH of 6.5-6.8. This range makes for happy worms and microorganisms and generally supports an abundance of readily available soil nutrients. Bigleaf hydrangeas, however, prefer moderately acidic soil with a pH range of 5.0 to 6.4. A soil pH toward the acidic end of the scale (5.0) will change the color of their flowers to blue. On the other hand, a soil pH toward the neutral end of the scale (6.5) will change their flowers to pink. Tip: It takes about 5 pounds of lime per 100 square feet to raise soil pH by 1 point and 2 to 3 pounds of sulfur per 100 square feet to lower soil pH 1 point.
To get a baseline measurement of the pH in your soil, you're going to need a soil test. Inexpensive test kits are available at garden centers, although you'll get more accurate results if you send a sample to a soil testing lab (ask your county extension office). If you decide to send your sample out for testing, be sure to request organic recommendations for adjusting your pH and ask for an explanation of what each amendment will do. These tests and recommendations can be important because different types of soil (e.g. sandy or clay) will change pH at different rates. If you change the pH too abruptly, plants and soil organisms won't have time to adjust.
If you're just trying to intensify a color you already have, a soil test may not be necessary. You simply need to make your soil more neutral to darken your pinks or more acidic to intensify your blues. The best time to amend your soil is in the fall after the plants go dormant.
Mother nature intended for white hydrangeas to stay white and no amount of soil amendments can change that. If your hydrangeas are white, enjoy them. They are going to stay that way. Sometimes as white plants age the flowers take on a pinkish tint, but that is about as colorful as white hydrangeas will ever get. The blue and pink Bigleaf hydrangeas like Mophead hydrangeas ( Hydrangea macrophylla) and Lacecap hydrangeas (Hydrangea macrophylla normalis) are what you need to grow if you want to change colors.
For a hydrangea to go from pink to blue, aluminum needs to be present in the soil. In one respect, this sounds easy, because you're adding something to the soil instead of taking something away. Most experts recommend applying it in liquid form by dissolving _ oz (1 Tbsp) of aluminum sulfate in a gallon of water. Plants should be watered well with regular water before applying this solution to avoid possible root burn.
Hydrangeas take up aluminum best in acidic soil, so before you apply aluminum sulfate the pH of your soil should needs to be in the 5.2 to 5.5 range. The aluminum sulfate will then work to lower the soil's pH even further. Organic amendments used to lower soil pH include coffee grounds, fruit peels, lawn clippings, peat moss and pine needles. Fertilizers can change soil pH, too. Bone meal, as well as fertilizers high in phosphorus, should be avoided. Instead, use a fertilizer high in potassium.
If you're starting with blue hydrangeas, your soil naturally contains aluminum and your soil is already more acidic. To change your hydrangeas to pink, you'll need to keep aluminum from becoming available to the plant. One way to do this is to raise the soil's pH by adding dolomitic lime or wood ash several times a year to edge up the scale toward 6.0-6.3. The higher pH will make it more difficult for the hydrangeas to take up any aluminum that is present. Fertilizers high in phosphorus will also help prevent hydrangeas from taking up aluminum.
You may be able to change the color of your hydrangeas, but a pale blue will never turn into a deep red. Intensity is somewhat predetermined by genetics, so if you want to change your pink color to a blue color, expect it to be as pale or intense as the original color.
One of the advantages to growing in containers is that you have complete control over the chemistry of the soil because it's contained. If you have naturally alkaline soil and want to grow blue hydrangeas, you can lower the pH of the soil in a container without negatively affecting nearby plants that prefer more alkaline soil. If you live in an area where blue hydrangeas grow naturally, you may want to consider growing pink hydrangeas in containers in order to easily control the amount of aluminum in the soil.
Weather can also play a role in color intensity, as can plant stress or environmental variables like nearby concrete walls or paths leeching lime. Don't try to change the pH of your soil dramatically over one season. Doing it over the course of several seasons will give beneficial soil organisms time to adapt and you'll get to experience the many shades of color in between your starting point and end results!
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How can I turn my hydrangea blue? I am hoping it is something that I would have on hand.
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I like your article about changing hydrangeas colours. You talk about lime added to the soil to change the acidity of the soil and plant colour.
What I was reading is that changing the acidity levels of the soil, as well as manipulating the plant's access to aluminum can change the colours of the hydrangeas. If eggshell can change or repel/attract aluminum, it would work.
"Generally, an acidic or low pH will induce 'blueness'; whereas, a higher or alkaline pH will induce 'pinkness or redness'. Work in England seems to indicate that higher aluminum content influences blueness more than pH levels."
eggshells are considered alkaline and here's an actual study saying whether they could be useful for liming: www.agronext.iastate.edu/
There is a purple hydrangea bush in our neighborhood. How was that effect achieved?
Hardiness Zone: 8a
Nana from Hattiesburg, MS
My grandfather use to put rusty nails in the ground around his hydrangeas. I am guessing the iron is what changed the colors. He had pinks, whites, blues and purples. It was one of my treats to get to help him do that.
I have a blue purple hydrangea in our backyard, it's just the variety. But I do know you can tweak the colors by adding things to the soil. I would google it on-line.
It's usually due to genetics. Why not just ask the owner? A little flattery will go a long way.
You can change the colors of most of the hydrangeas by changing the PH level of the soil surrounding the plant. You can also look this up on this site. I was reading up on it just this week. Good luck!
When we had finished building our home 20 yrs ago i planted a Hydrangea Plant and it came up all diffrent colors its a solid pink on one side and a solid blue on the other side and a two toned pink and blue and some purple in the middle and this is all on one bush i trim it down every yr and it comes up just the same i just take care of it and enjoy it and the Beautiful Blooms
Hydrangeas change color due to the acidic content of the soil. Depending on the soil you may get blue, pink or purple ones. I'm gussing that is why nails in the soil change the color of the flowers. You might ask your neighbor if she adds anything to the soil or if she just has soil that grows the flowers that color.
maybe one of these links will help
How do I turn a pink or white hydrangea blue?
I had some hydrangeas that were blue, and now they are pink. What can I do to make them blue again? My grandmother used to dump her coffee grounds on them, but I'm not sure that's what kept them blue.
By mara from Seattle, WA
How do you get blue hydrangeas?
Hardiness Zone: 8a
By Meg from GA
My grandmother always said to put a rusty nail in the ground next to your plant, that will change the color.
Rusty nail is for iron deficiencies. I think you add aluminum sulfate to the soil to get the blue color.
How do hydrangeas get their color?
Hardiness Zone: 8a
Martha from Cherryville, NC
Address: 115 W Main St, Lincolnton, NC 28092
Phone: (704) 736-8452
Contact your local county extension office for details, but I was told that it has to do with the level of ph in your soil. I bought one years ago because it was white and after transplanting it became a light blue.
I think I read somewhere that they get their color based on how acidic the soil is. If the soil is more acidic, the flowers are more pink in color. If it's more basic they are more purple in color.
Is it true you can add cold coffee to a hydrangea bush to keep it blue? How much do I use?
I started out with pink and blue hydrangeas in pots and they have now turned green. What can I do to get them colorful again?
Ii brought a red hydrangea on my holiday in Daylsford. I brought it home and sat it on my bench in its original pot and watered it the very next day. It turned purple why?
By Jess D.
I have a hydrangea I got from my daughter last year for Mother's Day. It's taking root, but I need to know how to add the ash and in what quantity, and where to place it. Dry on earth? Dilute in water in root area? Teaspoons or tablespoon? Thanks ahead of time.