Alum can indeed turn hydrangeas blue. Alum is a common name for aluminum sulfate, which is a compound that contains aluminum. When aluminum sulfate is applied to the soil around hydrangeas, it reacts with the soil to lower its pH level, making it more acidic. This acidity is what helps the hydrangeas produce blue flowers.
The process by which alum turns hydrangeas blue is quite fascinating. Hydrangea flowers can vary in color depending on the pH level of the soil they are grown in. In acidic soils with a pH below 6, hydrangeas tend to produce blue flowers. On the other hand, in alkaline soils with a pH above 7, they tend to produce pink flowers. This color change is due to the presence of aluminum ions in the soil.
When aluminum sulfate is applied to the soil, it dissolves in water and releases aluminum ions. These aluminum ions are then taken up by the hydrangea plants through their roots. Inside the plants, the aluminum ions react with other compounds to form complexes that can be incorporated into the petals of the flowers. This incorporation of aluminum complexes into the petals leads to the production of blue pigments, resulting in beautiful blue hydrangea flowers.
It is worth mentioning that the use of alum or aluminum sulfate is not the only way to achieve blue hydrangea flowers. Another option is to use elemental sulfur, which is a naturally occurring substance. Elemental sulfur works in a similar way to alum by lowering the pH of the soil and making it more acidic. This acidification of the soil helps the hydrangeas produce blue flowers.
One advantage of using elemental sulfur is that it is usually cheaper compared to aluminum sulfate. However, it is important to note that elemental sulfur takes longer to break down and have an effect on the soil pH. This means that it may take several months or even a year to see the desired blue color in your hydrangeas when using elemental sulfur. On the other hand, aluminum sulfate works faster and is often the preferred choice for gardeners who want quicker results.
In my personal experience as a gardener, I have used both aluminum sulfate and elemental sulfur to turn hydrangeas blue. I have found that aluminum sulfate tends to produce faster and more reliable results. However, I have also used elemental sulfur in situations where I had more time to wait for the color change or when budget constraints were a concern.
It is important to note that while alum or aluminum sulfate can help turn hydrangeas blue, it is essential to use them in the correct dosage and follow the instructions provided. Applying too much aluminum sulfate can lead to excessive acidity in the soil, which can be harmful to the plant. It is always a good idea to test the pH of your soil before applying any amendments and adjust the dosage accordingly.
To summarize, alum or aluminum sulfate can indeed turn hydrangeas blue by acidifying the soil and making aluminum available to the plants. It is a popular choice among gardeners due to its faster results. However, elemental sulfur is also an option, although it takes longer to break down and have an effect on the soil pH. Both options can be effective, and the choice depends on factors such as time constraints and budget considerations.
