This edited article about the hydrangea originally appeared in Look and Learn issue number 170 published on 17 April 1965.
If you ever see a gardener potting a hydrangea plant like this one and mixing iron filings with the soil do not imagine that he is a victim of absent-mindedness!
The gardener will be well aware of what he is doing – because iron filings mixed with the potting soil of a red or pink hydrangea turns the flowers blue. It is a trick practised by gardeners on this attractive flowering shrub when they want to change their colour scheme.
After the iron filings are added the gardener waters the soil with alum at the rate of one teaspoonful dissolved in a gallon of rain water.
Actually, the iron filings method of turning pink hydrangeas blue has been superseded today by “blueing powders” which do the same job more efficiently when added to the soil.
Many different varieties of these small-petal plants were cultivated in China and Japan centuries before their introduction to Western gardens. European gardeners are particularly fond of the plant for their terrace tubs, and they make a splash of colour in a tub on the patio or veranda of a town flat.
Hydrangeas are grown by taking cuttings, inserted in potting soil between May and August. The pots should be kept in a propagating frame in a greenhouse or in a closed cold frame. On sunny days the cuttings should be shaded from bright sunlight.
When the cuttings are rooted they need some air, and soon the young plants will be ready for separate potting in compost. By autumn or early spring the plants will have grown to the point where they will again need re-potting.
Nearly all hydrangeas lose their leaves in winter and they need a certain amount of protection from severe weather. It is a good idea not to let them suffer a temperature below 45 degrees Fahrenheit.
In early springtime hydrangeas grow fast and this is the time when they enjoy a regular meal of weak liquid manure. With the proper treatment you can get a magnificent head of bloom in the plant’s first spring from cuttings rooted the previous May.
In summer the flower heads fade and as soon as this happens is the best time to prune the plants. In late summer and autumn the flower buds form at the ends of the shoots ready for the following spring, which is why it is important not to prune the plants after the summer is over. Many of them are quite hardy, and make large bushes outdoors.