Hydrangeas can be colored blue – you just need to lower the pH of the hydrangea soil and add enough metal compounds at the right time. A game with a few variables that can still work, and there are also some home remedies that can help with a forced color change.
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The secret of the blue flowers
Plants use various pigments to create color in flowers and leaves: chlorophylls color light green to blue-green; Carotenoids color yellow, orange, dark green; Anthocyanins such as cyanidin and delphinidin color sky blue to black blue. Delphinidin is so called because it is also the dye in the bright blue / blue-violet field barbarian spur and was named after it “Delphinium consolida”. The secondary plant matter also provides a touch of blue in aubergines, violets and black currants, Cabernet Sauvignon grapes, cranberries and blueberries; and he is responsible for the fact that the flowers of hydrangeas turn blue.
In order for the color to work, the plant must have the genetic make-up to develop the color. If a plant has the genetic make-up to develop delphinidin, the result is not a “blue”, as the examples just mentioned show. Delphinidin is pH-sensitive and colors “its” plants depending on the pH value of the soil. In acidic soils with pH values below 6.5, delphinidin would turn reddish, in neutral soils with pH values between 6.5 and 7.5 blue-violet to purple, in basic soils with pH values above 7.5 the color always goes clearer towards blue.
If you have already dealt with blue hydrangeas, the statements about the pH values and tints of delphinidin could confuse you, because you can read everywhere that hydrangeas can only “turn blue” in acidic soils. That’s also true, hydrangeas don’t just need delphinidin to develop blue flowers. They only transform the delphinidin into blue color when metal salts (aluminum or iron salts) are added. However, these metal salts can only be absorbed by the hydrangeas in acidic soils in a form available to plants (apart from the fact that hydrangeas do not grow well or not grow in limestone soils with basic pH values).
Hydrangeas turn blue under the following conditions:
- The hydrangea species or variety contains delphinidin (is genetically capable of producing delphinidin)
- Well-known carriers of delphinidin are the normal garden hydrangea Hydrangea macrophylla and the plate hydrangea Hydrangea serrata
- Hybrid varieties can contain delphinidin if garden hydrangeas or plate hydrangeas were involved in breeding
- Only with white flowering hydrangeas will you never be “blue lucky” because they lack all of the genes for developing flower colors
- The soil must have a low pH below 5
- Metal compounds are added to this soil, which the hydrangeas can absorb in an acidic environment shortly before flowering
The acidic soil
In order for hydrangea flowers to turn blue, the soil around the hydrangeas must first have an acidic pH value. No problem a few years ago – “Hydrangea blue” was bought, along with the products suggested on the sales package for changing the soil pH value, and then half of the garden soil was forcibly acidified in order to produce wonderfully blue hydrangeas (practically not really, but rather rarely).
Today it is different: In the 1980s it was recognized that acid rain led to forest death, since then environmental efforts in government and society have ensured that the rain today (often, almost) has neutral values again. As a result, the realization dawned that the soils of our country not only need to be protected from traffic and industrial emissions. But that these are separate areas of life in which vast numbers of microorganisms and (larger) small animals work and are just as sensitive to acids as they are to pesticides. That is why the Germans’ favorite plants growing in acidic soils are now bred in such a way that they also grow in neutral soils (although many of these plants like acidic bog soils, they have always grown in soils with neutral pH values),
Scientific knowledge about the composition of our soils and the susceptibility of this sensitive biotope to failure are slowly penetrating the population; Since the “Year of the Soil” (2015) at the latest, more and more garden owners have been looking after their garden soils. This also includes maintaining a healthy pH value, which in normal garden soil is around the neutral range (or slightly below; the greatest intersection of plant nutrients dissolves best at pH values of 6.3 – 6.8). Any gardener who has understood or lived through these new findings and developments will therefore refuse to change the pH value of their garden soil through external violent interventions.
In the case of the blue hydrangeas, the sensible treatment of the soil seems to collide with the meaning of garden culture (garden as a human-shaped image of the natural landscape), but this does not have to be the case:
- Unusual designs have adorned gardens for thousands of years
- The trends that were not feasible disappeared, never to be seen again
- For example, “florists” bred spotted georgines (dahlias) that could not withstand everyday life in the garden
- Ximenia were supposed to bring fruits and sandalwood, but as semi-parasites they tapped the neighboring roots
- “Hotbeds” brought great vegetables, but also stink and pests
- The feasible trends remained or came (come) again and again into fashion
- E.g. Topiary became a lasting success because many plants don’t care how they are pruned
- And a zen garden in Europe can also be designed with and not against the plants
- It is exactly the same with the “blue hydrangeas”
- If the acidic earth is put in a bucket, not a single bed needs to be “poisoned”
- The blue hydrangeas decorate the garden wherever you want
You can of course do whatever you want with your beds, theoretically pouring liters of vinegar essence into the bed (practically not, if enough of it gets into the sewer system, that can cause quite a problem). But acidifying the garden soil is also not a particularly promising route to blue hydrangeas, because you cannot calculate the required amounts of acid and metals really well and control the spread in the soil even worse.
Color hydrangea flowers blue
The flowers of hydrangeas in the tub can be easily colored blue with the following (house) remedies:
- Means to lower the pH value
- Lawn cuttings, leaf compost, needle litter and coffee grounds are suitable household remedies
- If the hydrangea is already potted and sits well in the bucket, vinegar will do the same
- Hard water or soda (baking powder) helps against inadvertently acidic soil
- pH measuring strips, from garden centers, hardware stores, pharmacies
- Metal compounds that react with delphinidin: alum or aluminum sulfate
- Aluminum sulfate is a combination of aluminum and sulfur
- The colorless powder occurs naturally in minerals (sulfuric acid clay) or is obtained from alums
- Alum traditionally describes the crystallized sulfuric acid double salt of potassium and aluminum
- This combined metal sulfate is also known as potassium aluminum sulfate
- Today alums with a different composition are also used and subsumed under the term “alum”
- In the household, alum can be found in the classic razor pen, which stills the blood after small shaving cuts
- If you don’t want it to disappear dissolved in hydrangea soil, you can get potash alum and aluminum sulphate in the pharmacy
- Iron would theoretically work and should be part of the fertilizer as an important nutrient for hydrangeas
- “Making blue” with iron is difficult and not practical
- Better forget about commercially available hydrangea blue
- With this “blue fertilizer” the hydrangea either gets too much blue or too much fertilizer
- In the past, washing water with laundry blue (starch flour with blue pigments) was tipped onto the hydrangeas
- However, there is no practical experience for this procedure
- The similarly stored coloring with blue ink in the irrigation water should not work, however
If you want to lower the pH value of the bucket soil with lawn clippings and the like, it is difficult to make recommendations on the quantities; you would have to use pH test strips to find the optimal result. For acidification with vinegar and blue coloration with alum or aluminum sulphate, empirical values exist for 30 l pails, which are applied below. This is how the blue dyeing of the hydrangea works step by step:
- Bring the pail earth to pH 4.5 – 5 by mixing in the acidifying substances
- Or brutally mix a generous splash of vinegar essence into the watering water
- Determine the pH value with test strips, readjust if necessary
- Take into account the pH value of the irrigation water:
- Strongly alkaline tap water causes low pH values to rise again quickly
- Before the hydrangeas begin to flower, it is time to adjust the pH
- As soon as the time comes, approx. 5 g of aluminum sulfate or alum per 30 l of soil are dissolved in 1 liter of irrigation water
- While the flowers are in bloom, the hydrangea is watered 2 to 4 times with this solution
- The optimal time is disputed
- Experts tend to assume that the flowers are “ready-made” when they are 2 – 3 cm in size and are then difficult to recolor
- They recommend giving the alum by then
- Practitioners recommend that the acidifying metal compounds be administered exactly when the flower roots are about to develop color
- Then the first petal should turn bluish from the tip
- If it doesn’t, the hydrangea gets a little “blue feed”, which at least benefits the following flowers
- Latecomer flowers can usually use a dash of blue
The whole thing is a game with pH values, metal compounds, various components in potting soil and water and a variably functioning plant metabolism. So you don’t flick a switch to “blue”, but screw on many small cogs to which the hydrangea gradually reacts. Perhaps you will find the perfect mix right from the start, perhaps it takes a certain amount of experience before the hydrangea shines blue. This is one of the reasons why it is advisable to color hydrangeas in the tub, in the garden it is almost impossible to fall back on past experiences with a little more or less alum, acid, etc., because there are even more factors involved.
Conclusion
The blue coloration of hydrangea flowers is feasible, but a rather difficult exercise in the garden if you do not want to acidify half the garden soil. Even in the bucket, you will not necessarily see a blue blossom immediately; But that’s no reason to be angry, because every shade on the way to blue is beautiful to look at.