Hydrangeas are among the most beautiful shrubs in the garden. Their gorgeous blooms make them an instant eye-catcher, and their preference for partial shade makes them one of the most popular plants for the front yard. Depending on the variety, garden hydrangeas bloom between June and September and enchant with lush flower umbels in white, pink, red, blue, purple and green. But what makes this ornamental shrub so special is its ability to change flower color. What this is due to and how to turn hydrangeas blue, we reveal in the article.
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What changes the color of hydrangeas?
Hydrangeas change color (except for the white-flowering species) depending on the pH of the soil in which they grow. The more alkaline the soil, the pinker the flowers. Thus, pink hydrangeas can be dyed blue if the acidity of the soil is increased.
Not all species can be dyed blue
Hydrangeas can bloom blue only under certain conditions. In addition to the acidic soil, the variety plays a crucial role. Only the varieties that contain a certain plant pigment called delphinidin can be colored blue.
If you buy a new hydrangea, pay attention to the plant label. It is usually noted there whether or not color change is possible with that particular variety. The plant itself can also tell you if it is a chameleon or not. For this, you should take a closer look at the flower color – if the hydrangea blooms pale pink, in most cases the color change is possible. On the other hand, species with white or intense pink flowers can not be colored blue.
Blue coloring is possible with these hydrangeas: farmer’s hydrangeas, garden hydrangeas, and plate hydrangeas, such as the “Forever & Ever” and “Endless Summer” varieties.
How to dye your hydrangeas blue.
The first thing you need to do if you want to change the flower color of your hydrangea is to measure the acidity of the soil, that is, to determine the pH. To do this, you should first take a sample. In this article, we explain how to do this.
To promote blue hydrangea flowers, you should grow the plant in soil with a pH of 5.2 – 5.5. For intense blue color, the pH should even be below 5.0. If your soil is more alkaline, you should try to lower the pH to change the flower color to blue. You can use a variety of remedies to do this.
Change color with home remedies
There are several home remedies that can help keep soil pH low. Coffee grounds, for example, are perfect for plants that need acidic soil. The same goes for leaf compost and needle litter. You can work these additives into the soil to lower the pH of the soil. It is also recommended that you plant hydrangeas in hydrangea or rhododendron soil, which are also acidic.
But beware. Some home remedies, such as vinegar and vinegar essence, have a low pH, but they are completely unsuitable if you want to make the soil more acidic. Vinegar is even a real plant killer, so you should keep your hands off of it if you want to turn your hydrangeas blue.
Dyeing hydrangeas blue with alum
In order for hydrangea to have blue flowers, the plant still needs the mineral alum. It contains aluminum ions that are responsible for changing the color of the flowers to blue. You can buy the alum either in pure form in the pharmacy, or even easier – get a suitable hydrangea fertilizer, which is already enriched with the mineral.
But the application of the pure alum is also not difficult. The powder is simply added to the water – 3 g per liter of water is sufficient. The less calcareous the water, the better, of course, rainwater is best. From the beginning of May, you should then water the hydrangeas with the alum solution once a week over the course of 4 to 5 weeks.
The color change works best with hydrangeas in a tub, because it is easier to regulate the pH of the soil in a tub.
How long does it take for the flower color to change?
To get uniformly blue blooms, the pH of your soil will likely need to be adjusted regularly. To do this, carefully work acidifying soil amendments into the top layer of soil around the root when you normally fertilize your hydrangeas, usually in early spring. Even if you start from an alkaline or neutral soil and try to make it more acidic, keep in mind that your hydrangeas will not suddenly turn blue overnight. It will probably take several applications of fertilizer to make the soil acidic enough, and if your hydrangeas have already bloomed pink, you may not see blue flowers until next year.