Perpetually confused as to when you should prune your hydrangea bushes? The Endless Summer® bigleaf hydrangea (Hydrangea macrophylla 'Bailmer') is your best option, as it flowers on both this year's new growth and last year's woody stems. Provide a moist, humus-rich soil in partial shade and watch the flowers dazzle across the summer in shades of pink, lavender or blue, based on soil pH.
The bigleaf hydrangea (Hydrangea macrophylla) is a round-shaped deciduous shrub native to Japan. In mid- to late summer each year, these shrubs display large, showy clusters of flowers, either sterile or fertile. The bigleaf hydrangea is divided into two types: lacecap or Hortensia, based on the shape and make-up of the flower cluster. Lacecap flowers have tiny fertile blossoms in a flat-topped cluster surrounded by sterile flowers with large, showy sepals that look like petals. Hortensia flowers, also called mopheads, only form the showy sterile flowers in a globe-like mass.
In 1983, Vernon Glen Black of Cottage Grove, Minnesota first encountered a bigleaf hydrangea that performed well in the climate of St. Paul, Minnesota. Tested and then named 'Bailmer' by Bailey Nurseries, Inc. of St. Paul, it was also assigned a trademark name of Endless SummerÂ®. It also has a United States Patent Number of PP15298.
Other than having exceptional cold winter hardiness, surviving in USDA Zone 4, 'Bailmer' typically has disease-free foliage and an ability to continually flower all summer as long as old flower heads are cut away, a process called deadheading.
Although bigleaf hydrangeas usually are pruned only immediately after the summer flowering, 'Bailmer' can be pruned in summer, fall, or early spring. Since it produces flower buds on woody old-growth stems as well as on current-season growth, this cultivar indeed lives up to its trademarked name of Endless Summer®, as it will produce flowers continually up until fall frosts.
This selection is a Hortensia, or mophead, type of bigleaf hydrangea. The flower heads are spherical and comprised of scores of sterile flowers that each have four sepals, or petal-like modified leaves.
The color of the flowers is affected by soil pH. In an acidic soil (pH less than 7.0), flowers attain a bluish color. The more acidic the soil, the deeper the shade of cobalt blue that develops. In alkaline soil (pH greater than 7.0), the flowers blush in tones of pink, culminating in an intense rose shade in higher alkaline ground. Variable shades of pink, lavender and light blue can occur within the same flower head or same plant when growing in soils that are near neutral in pH (pH 6.5 to 7.5).
To drop the soil pH, to make it more acidic, gardeners scatter aluminum sulfate on the ground 3 to 6 months in advance of expecting flowering. To raise soil pH, to make it more alkaline, lime is scattered well in advance of the summer flowering.
Plant bigleaf hydrangeas in partial shade, as in the dappled light under large shade trees, the edges of woodlands or shaded side of a building. Soil must be moist but well-draining and rich in organic matter such as compost, leaf mold, manure or mulch.
In cool-summer regions or where the soil is consistently moist, bigleaf hydrangea can tolerate more exposure to direct sunlight, upwards of 6 hours of direct sun each day. In general, however, the foliage health and durability of the flower color is best when no more than 4 hours of direct early morning or late afternoon sun reaches the shrubs.
Selection 'Bailmer' is hardy in USDA Winter Hardiness Zones 4 through 9. It is a deciduous plant that will lose its foliage in winter, even in Zone 9.
If never pruned, 'Bailmer' will reach a mature height of 4 to 6 feet, and an equal spread. However, annual pruning of shrubs in summer after the initial flowering display can reduce plant size and keep them in the range of 3 to 4 feet in height and spread. In cold winter regions, winter temperatures can naturally kill back stems of this hydrangea to the ground, and the plant will rejuvenate in spring and still bloom on the current growing season's stems.