Mophead hydrangea (Hydrangea macrophylla) was part of every garden I remember from childhood.
Usually they were situated on the north side of the house in perpetual shade.
In early summer the huge rounded flower clusters looked like giant scoops of ice cream.
These hydrangeas are native to Japan but probably were first introduced into China before they made it west to Holland. The Dutch grew them in greenhouses and introduced new varieties into other European countries.
The mopheads are cold hardy only to Zone 6. In the U. S. they are strictly a southern thing and southern gardeners have truly embraced then.
Most hydrangea bloom clusters are a combination of showy sterile flowers that look like paper cutouts and tiny fertile flowers that can actually produce seed. It is easy to see both these flower types in a lacecap hydrangea inflorescence. The mophead cousins have only sterile flowers and are not capable of producing fruit capsules or setting seed.
The hydrangeas of my childhood were usually pink. I grew up in a town that was situated on Blackbelt prairie soil. The soil was derived from limestone and so pH was high or alkaline. In this type soil there is little free aluminum and mophead hydrangea blooms are often pink.
As a result, the blue flower clusters were more exotic to local gardeners and many resorted to chemistry to obtain the desired hue. Iron sulfate, aluminum sulfate or ground sulfur were used to lower the pH. The resulting acid soil contained more free aluminum and flowers were blue.
Creative gardeners sometimes even put sulfur compounds only on one side of the shrub resulting in a half pink / half blue / purple in the middle blooming shrub. It was also common practice to bury rusty nails when planting one of these hydrangeas. As the nails continued to rust in the soil they served as a timed release source of iron and the blooms remained blue.
During the years that I worked as a retail garden center salesperson, I sold lots of mophead hydrangeas. They were also called bigleaf hydrangeas, garden hydrangeas, French hydrangeas or even “high geraniums”.
I advised my customers that no matter what they called the plant, it should be sited in an irrigated bed or in a situation where water could be supplied during drought.
The most common cultural question that customers asked me was about the pruning needs of the plant. This hydrangea blooms on old wood. In other words, if the shrub was cut to the ground or burned back during a hard winter it would skip a year of bloom. So old established plants can be pruned like any old fashioned shrub – by cutting one third of the oldest stems to the ground. Two-thirds of the stems remain and are capable of flowering. This pruning method also will stimulate new growth from the shrub’s base and enhance the natural mounding growth habit.
Younger plants without so many stems can be shaped by cutting stems that flowered in the current season back to the desired height. This is best done in summer after flowering when dried blooms are still present. So a few of the stems with dried flowers can be headed back and the remaining stems will surely bloom the following season.
The mopheads are not what I would call a subtle plant. They are startling in full bloom with huge leaves and many rounded unusually colored flowers.
I think their main claim to fame is their usefulness in floral design. Fresh flower stems will last for days. They can then gradually dehydrate in the vase or hanging in a dark well ventilated area. They retain their color and are popular in wreaths and dried flower arrangements.
Most old varieties bloom for about a month in late spring and early summer. A few cultivars do bloom on new wood and so can rebloom through the summer whenever new stems are produced. Penny McHenry, a hydrangea expert in the Atlanta area, discovered a reblooming variety that is called ‘Penny Mac’ in the trade.
A similar reblooming variety was patented and given the name ‘Endless Summer’.
I don’t much care for the concept of an “Endless Summer”. Here in Mississippi most of us are well over our romance with summer by the middle of July. The thought of an endless Mississippi summer makes my head hurt.
So… I usually spec ‘Penny Mac’ on my landscape drawings. It does rebloom and is cheaper because it is not a patented plant.