What fertilizer is suitable for blue hydrangeas? How to dye hydrangea blue and keep the color? Our tips on how to deal with blue-colored hydrangeas.
Peasant hydrangeas (Hydrangea macrophylla) are special when it comes to the color of their flowers, which not only depend on the hydrangea variety, but also on the soil conditions. Garden hydrangeas and hydrangeas of species H. macrophylla, which are summarized under the name farmer's hydrangea, bloom in pink, red, violet, white or even blue. But blue and purple hydrangeas quickly lose their flamboyant color and turn red or pink - we explain how to avoid this.
In the following, we show the conditions under which hydrangeas bloom blue and what the soil conditions have to do with it. You will also find instructions on how to dye your hydrangeas blue yourself.
What makes pink hydrangeas blue?
The reason for the change in color of hydrangea flowers of pink and red varieties is due to the flower pigments of the plant. The red or blue dye is called delphinidin and belongs to the anthocyanin group. This color molecule changes its structure with the help of metal ions (aluminium, iron) and forms so-called chelate complexes. These give the hydrangea blossoms an intense blue color.
In order to color a hydrangea blue, the blossom must first ideally be pink. If their color is too red, the combination with blue delphinidin results in a violet hue. Since white hydrangeas contain no delphinidin at all, you can't turn them blue either.
Requirements for dyeing hydrangeas blue:
Hydrangeas need acidic soil. This is characterized by a pH below 6. Hydrangeas preferably have a pH of around 4.5, they are well adapted to these acidic soil conditions. If the pH value is too high (> 4.5), the iron and aluminum ions that are important for the blue color are presentSoil is no longer readily available and its uptake by the hydrangea roots is severely restricted.
Another prerequisite for successful blue dyeing is that the plant to be dyed is the right species of hydrangea. In addition to white varieties of species H. macrophylla, other hydrangea species such as velvetleaf hydrangea (Hydrangea aspera ssp. sargentiana), climbing hydrangea (Hydrangea petiolaris) and panicle hydrangeas (Hydrangea parniculata) do not turn blue either. Only peasant hydrangeas with violet and pink flowers can achieve this color tone.
Furthermore, the hydrangea must be he althy and sufficiently supplied with nutrients and water. In order to ensure an adequate supply of nutrients, hydrangeas should be fertilized annually with a suitable fertilizer such as our Plantura hydrangea fertilizer.
How to test the pH of blue hydrangeas
An acidic soil (soil pH <5) zählt zu den Grundvoraussetzungen für blaue Hortensienblüten. So Testen Sie den pH-Wert Ihres Bodens:
- Put about 100g of your soil in a mason jar.
- Add 100 ml (distilled) water and mix thoroughly.
- After 10 minutes you can dip a pH test strip into the solution and read the result on a color scale (you can get the pH paper in hardware stores or pharmacies, for example).
- However, the result determined in this way is not exact: the actual pH value is about 0.5 points lower than indicated.
- You can get a more accurate and faster measurement result with a special measuring device, a so-called soil pH meter.
If your pH reading is above 5, you should acidify it as described later in the article.
The lower the pH value, the bluer the hydrangeas become:
- Slightly acidic soil (pH around 5.5): the blue color no longer develops and the blue or purple hydrangeas turn pink or red again.
- Highly acidic soil (pH around 4): the blue hydrangeas will keep their blue tint, pink hydrangeas will turn blue.
To achieve the color change of the hydrangea flowers from pink to the popular hydrangea blue, two main steps are important. The first thing to do is to acidify the soil in which the hydrangea grows. A low pH value is the prerequisite for the uptake of aluminum and iron ions,which can be supplied second by the addition of alum dissolved in water. Finally, maintaining acidic soil pH is important to avoid re-staining.
How to dye pink hydrangeas blue
- To achieve a pH reduction right at planting, you can either use special (usually peat) hydrangea or rhododendron soil or mix your garden soil directly with peat. Since hydrangeas and other ericaceous plants can no longer efficiently absorb the essential iron if the pH value is too high, this measure is necessary anyway to prevent hydrangeas from becoming iron deficient. The acidic pH makes the aluminum in the soil available and the hydrangeas turn blue.
- In order to achieve a faster and more intensive color change in the hydrangea blossoms, you can also artificially add aluminum to the soil. More precisely, potassium aluminum sulphate (alum) or aluminum sulphate is used. You can even get these aluminum compounds in pharmacies.
To produce a blue color right from the start, water the hydrangea during the budding phase, or until the beginning of June, with a solution of three to four grams of alum per liter Water. You should repeat this about four to five times at intervals of 7 days. - You can get "Blue Hydrangeas" from garden retailers. These agents temporarily lower the pH value and turn the hydrangeas blue due to the aluminum. Unfortunately, "Blue Hydrangea" does not keep the flowers permanently blue, but acidifying the soil has a lasting effect. Please do not confuse the hydrangea blue with blue grain. Blue Grain is a universal fertilizer that gets its name from its own color.
Tip: When fertilizing with alum, always use rainwater or tap water acidified with peat to prevent the pH from being raised by the hard, chalky tap water.
Are there home remedies to turn hydrangeas blue?
If you don't want to buy environmentally harmful peat and hydrangea blue or alum, you can try using home remedies to cause the hydrangea blossoms to turn blue. Grape pomace (a by-product of wine production), the needles of conifers or acidic primary rock flour (bas alt, granite) are suitable for lowering the pH value of the soil. Iron and aluminum ions are in mostNatural soils are available in sufficient quantities and do not have to be added. For potted plants, therefore, mix in a good amount of garden soil to introduce iron and aluminum. Incidentally, an exception here is the acidic moor soil, which is found on former, drained moor areas - this is very poor in iron.
How to keep hydrangeas blue
When planting or transplanting blue hydrangeas, the most important thing is choosing the right substrate. The pH value of the soil must then be kept permanently low in order to avoid re-discoloration. One way to get acidic soil with a pH value of 4.5 is to only use low-lime rainwater for watering, which is acidified with peat, vinegar or bark mulch.
You should also regularly mulch with leaf compost, lawn clippings or pine litter, as the organic material releases acids into the soil that lower the pH value. The regular use of grape pomace and sour bedrock meal also helps to keep the soil acidic.
You can use a soil pH meter to check the pH value of the substrate so that you can react in good time to an increase in pH value to be able to.
Tip: If you don't want other plants in the bed to be disturbed by the low pH value, you can also grow your blue hydrangeas in a tub. There it is anyway easier to keep the soil acidic due to the smaller soil volume. Alternatively, it is advisable to create a "bog bed" in which only acid-tolerant plants grow. These include species such as the beautiful berry (Gaultheria procombens) or the lavender heather (Pieris japonica) as well as numerous grasses and the beautiful skimmia ( Skimmia japonica).
Summary Coloring Hydrangeas Blue:
Two conditions must be met for your hydrangeas to turn a beautiful blue:
- Only pink or red hydrangeas of the species Hydrangea macrophylla can be colored blue or dark purple.
- The soil must be acidic, i.e. the pH value must be around 4.5 and kept low: To do this, regularly mulch with acidic material and water with acidified rainwater.
- Due to the smaller volume of soil in the tub, the blue color is easier to achieve than in the garden.
- Aluminum ions must be available in the substrate: the hydrangeas can be watered with aluminum sulphate (alum solution orspecial fertilizer), but aluminum is usually present in natural soils.
In addition to the right pH value, there are other factors that ensure that hydrangeas bloom magnificently. You can find out everything you need to know about caring for hydrangeas in this article.