Methods for Altering Hydrangea Blooms: Simple Adjustments for Pink, Blue, and Purple Blossoms
### How to Change the Colour of Hydrangeas by Adjusting Soil pH
Hydrangeas, known for their vibrant and versatile blooms, can have their colour changed by manipulating the soil's pH levels. This chemical adjustment allows gardeners to customise their garden displays year after year.
#### Understanding pH and Hydrangea Colours
The colour of hydrangeas, particularly bigleaf, mophead, lacecap, and French types, is influenced by the soil's pH, which controls the availability of aluminium, a key element for blue flower formation. White-flowered hydrangeas, such as oakleaf and panicle hydrangeas, do not change colour based on pH.
| Soil pH Range | Hydrangea Colour | Aluminium Availability | |---------------------|-------------------------------|-----------------------------| | pH 4.5–5.5 (acidic) | Blue | Available | | pH 5.5–6.5 (mid) | Purple, mauve, or mixed colours| Somewhat available | | pH 6.5+ (neutral/alkaline) | Pink/reddish-purple | Unavailable |
#### Changing Soil pH to Achieve Desired Colours
To make hydrangeas **blue**, decrease the soil pH by applying elemental sulfur or ammonium sulfate to acidify the soil, aiming for a pH of 5.0–5.5. Additionally, water with dissolved aluminium sulfate, which both acidifies the soil and supplies aluminium, the crucial nutrient for blue flowers. This process may require multiple attempts and patience.
To make hydrangeas **pink**, raise the soil pH by adding lime (calcium carbonate or dolomitic lime), aiming for a pH above 6.5. Avoid fertilisers that contain aluminium. Again, gradual and monitored application is key, as rapid changes can stress the plant.
#### Practical Tips
- Before adding amendments, test your soil pH to know your starting point. - Only certain hydrangea types change colour; choose mophead, lacecap, bigleaf, or French hydrangeas if you want adjustability. - Colour changes will not be instant and may require maintenance to sustain the desired pH level.
> "For a hydrangea with blue flowers, the soil pH should be acidic with a pH between 5 and 5.5. Acidic soil allows aluminium to be available to the plant and results in blue flowers. A soil pH of 6 or more will cause aluminium in the soil to not be available to the plant and results in a hydrangea with pink flowers."
#### Summary
| Desired Colour | Target Soil pH | Main Action Needed | |---------------|---------------|--------------------------------------| | Blue | 5.0–5.5 | Acidify soil, add aluminium sulfate | | Purple | 5.5–6.5 | Mildly acidic to neutral soil | | Pink | 6.5+ | Raise pH (add lime), no aluminium |
Hydrangeas planted in pots offer more control over the soil conditions and thus the colours. Some popular varieties that can change colours include Nikko Blue Hydrangea, Endless Summer hydrangeas, and Let's Dance® Starlight Hydrangea. When transplanted, hydrangeas may change colours on their own due to adjusting to their new environment.
However, there are limitations to changing the colours of hydrangeas, such as not being able to change white hydrangeas to pink or blue, and difficulty in changing the intensity of a hydrangea bloom's colour. To ensure hydrangeas get the aluminium they need, avoid using lime when aiming for blue flowers.
Adjusting the colour of hydrangeas is a unique aspect of gardening where chemistry meets horticulture, allowing gardeners to create a stunning and ever-changing display in their gardens.
- To achieve blue hydrangea flowers, it's essential to have acidic soil with a pH range of 5.0 to 5.5, allowing aluminium availability and promoting blue blooms.
- For pink hydrangea flowers, gardeners should aim for a soil pH of 6.5 or higher, which can be accomplished by adding lime, and avoid fertilisers containing aluminium.
- When deciding on hydrangea species for colour change, consider mophead, lacecap, bigleaf, or French hydrangeas that are known to respond to pH alterations.
- To maintain the desired colour of hydrangeas, test your soil pH before making any amendments, adjusting the soil pH can be a gradual process requiring patience.
- Organic and decorative elements in home-and-garden settings can enhance the aesthetics of the landscaping, making a beautiful and personalized outdoor living space, with blooming blue or pink hydrangeas as part of the lifestyle choice.
