Many folks were disappointed that their hydrangea shrubs had few, if any, flowers last year. It was thought to be caused by the exceptionally harsh winter
There are many species of hydrangea, but the genus, Hydrangea macrophylla, encompasses most planted by homeowners in their gardens.
H. macrophylla is divided into two groups based on the shape of their flowers. The mopheads have a large round form that may be red, pink, white, blue, violet and green — and many shades in between. The lacecaps, similarly colored, are flattened corymbs with fertile flowers in the center surrounded by showy clusters of sepals of varying sizes.
The hardiness zones for H. macrophylla are 6 to 9. Effectively, a hydrangea should be able to sustain a temperature of minus-10 degrees. But in the real world, temperatures as low as 12 degrees — and late fall or early spring freezes — may reduce the flowering capability of this hydrangea.
The flower buds of H. macrophylla form in the summer and the autumn in response to shortened days and cooler temperatures. The bud must be chilled for 1,000 to 1,200 hours (about seven weeks) to satisfy the requirement of bud dormancy.
As the temperatures warm up, buds break, shoots emerge and flowers develop. If this occurs at the end of February, as it did last year, and may again this year, flower buds and vegetative stems will be killed. The plant may regenerate from its base in the spring, but it will not flower. It is root hardy, but flower bud tender.
H. macrophylla blooms on new wood, on the current year’s woody stems. If a shrub needs pruning, this should have been done last year when it had just finished blooming. Do not prune it now — you will be cutting off any developing flower buds.
My favorite H. macrophylla,, which I have grown for about 15 years, is a cultivar called ‘Blue Billows.’
This lacecap, Hydrangea serrata, was originally grown from seed collected in the mountains of Korea and selected by Dr. Richard Lighty of the Mount Cuba Center in Hockessin, Delaware. The outer sterile flowers are blue with a flush of pink and the inner fertile flowers are a darker blue.
H. serrata variety was a subspecies of macrophylla until very recently, when the taxonomists separated it out as its own species. It has all of the characteristics discussed previously as H. macrophylla. However, the leaves are smaller and it has brilliant copper-red fall color. It flowers from June to October and as fall approaches the flowers turn upside down, showing pink undersides.
I have located it in fairly heavy shade with well-drained soil. It is described as a “robust plant.”
Most recently when I moved it to a shadier location, the large root ball fell into two parts. And then I noticed it had produced three smaller plants through suckering or air layering.
It is a dense shrub, growing about 3 feet tall and wide, full of foliage and flowers — so much so that I did not realize I had those four extra plants until I began to move it.
This is a low-maintenance shrub that can be used as a foundation plant or in a shrub border. And it will reward you with proliferation that you can keep or give to friends. It was selected as a Gold Medal Plant in 1990 by the Pennsylvania Horticulture Society.
The color of the flower changes, depending on the concentration of aluminum ions in the soil. The concentration is higher in acidic soil and lower in more alkaline soils. For most H. macrophylla and H. serrata cultivars, blue flowers will be produced in acidic soil (pH 5.5 and lower), whereas neutral to alkaline soils (pH 6.5 and higher) will usually produce pink flowers. Between pH 5.5 and pH 6.5, the flowers will be purple or a mixture of blue and pink flowers will be found on the same plant.
However, the most consistent rule in growing hydrangeas is that there is no hard and fast rule and there is a great deal of variability.
Another hydrangea that should be talked about at this time of year is Hydrangea arborescens. It also comes in both mophead and lacecap flower forms. Some popular cultivars are called ‘Annabelle,’ Invincible Spirit,’ and ‘Grandiflora.’ These all bloom on new wood. So now, in late winter, is the time to cut them to the ground and lightly fertilize them.
The flowers are often too heavy for the stems to hold the plant upright, so place a support structure around it before the growth begins.
In June or July, the new plant will produce beautiful flowers for several weeks.
If you want to dry them, as the flowers fade, cut the stem at the base and strip off the leaves. Cut them to a desired length and hang them upside down. They are excellent dried flowers and may also be spray painted for added color.
Ann Auerbach is a Rutgers Master Gardener in Camden County. Send your lawn and garden questions to njgarden@camden county.com, and include ‘Courier-Post’ in the subject line if you’d like to be considered for write-up in the column. A Rutgers Master Gardener will respond to all questions received. Visit our offices at the Camden County Environmental Center, 1301 Park Blvd., Cherry Hill, 08002, (856) 216-7130. Master Gardeners are there from 9 a.m. to noon, Monday through Friday.
