What you need
A hydrangea plant
Advertisement
A soil pH test kit
Aluminium sulphate or garden lime powder
RECENTLY, my friend emailed me with a question:鈥漌hat鈥檚 happened to my hydrangeas?鈥� She had been given a bush with beautiful blue flowers, yet within a few months they had turned a drab green.
Hydrangeas are a group of plants that are usually a wonderful addition to a garden as they bear large, striking flowers for several months from midsummer. Some popular varieties also have a unique quality: the colour of their blooms is remarkably sensitive to their growing conditions.
Depending on soil chemistry, these hues can range from dark red through pink and green to the deepest blue. While this may be annoying if you have your heart set on one colour, it also lets canny gardeners play with their palette.
Hydrangeas鈥� malleability stems from a pigment in their flowers called delphinidin-3-glucoside that is blue when it binds to aluminium and red when it doesn鈥檛. Under acidic conditions with a pH of around 5 or below, the plant can take up more aluminium from the soil, making the flowers blue. With neutral or alkaline conditions, less aluminium means pinker flowers.
Many home remedies are said to alter soil鈥檚 pH, like sprinkling epsom salts or coffee grounds on it, but these don鈥檛 always work well. Better to buy commercial products such as aluminium sulphate, which both lowers pH and boosts aluminium, or garden lime powder for alkalinity. It is easy to find your soil鈥檚 pH using test kits sold at garden centres.
It isn鈥檛 all plain sailing, though. There are many different species and varieties of hydrangea, and some incline more to one hue than others, so check the label before you buy if you have a particular colour in mind.
Soil in some areas can also be stubborn. 鈥淚f you garden on a chalk soil or limestone, no matter how acid you try to make the soil, it will act as a buffer and restore to alkaline,鈥� says Guy Barter at the UK鈥檚 Royal Horticultural Society. 鈥淚n those situations, a container is your best bet.鈥� Be sure to use a planting compost with the right pH, too.
Back to my friend. By the time I replied to her message, her flowers had changed colour again. She lives in Oregon and her plant had been subjected to showers of ash from the wildfires that are ravaging the western US states.
Within days, her hydrangeas were multicoloured, with different parts of the same flowers now pink, white and green. That is because wood ash contains compounds that make soil alkaline, although I am surprised how quickly they acted in this case, as colour changing often takes months.
My friend plans to continue pinking up her flowers in this rough and ready way by applying wood ash from her home fireplace, rather than buying products from a store. This is fine as long as the wood hasn鈥檛 been treated with preservatives.
The science of gardening appears every four weeks
Next week
Science of cooking
These articles are posted each week at
