Master tips from a Master Gardener (2/16/17)

Bill Koellner · Wednesday, February 15, 2017
Most Iowans have many different types of plants in their landscape. One of the most popular plantings sold for landscapes is the hydrangea bush. It is popular for many reasons, beauty, lushness of the vegetation, large and showy flowers, adaptability to soils in Iowa, and resistance to disease, many of which can be controlled using environmental solutions.

There are five types of hydrangeas grown in Muscatine County. Muscatine County’s plant hardiness zone is 5b which are temperatures between -23 and -26 degrees Fahrenheit. This zone covers southeast Iowa to include Iowa City, Clinton and southwest to Taylor County.

Northwest of that location is zone 5a which are temperatures between -26 and -29 degrees Fahrenheit. The five hydrangeas that will survive in zone 5b are called smooth, panicle, bigleaf sometimes referred to as mophead or lacecap, oakleaf and climbing hydrangeas. These hydrangeas share some, but not all, of the same flowering habits.

The bigleaf mopheads come in two general varieties. The classic ones only bloom in spring and the newer hybrids called remontant or reblooming varieties, bloom from spring in to fall. The spring bloomers form flowers on buds developed during the previous late summer and fall’s old wood.

Pruning these shrubs during fall, winter or early spring will remove the flower buds with a loss of blooms for that season. Hydrangeas in the reblooming group have last season’s buds as the others do but also form buds in the current summer, which bloom that summer and fall. If these are pruned winter or spring, the spring blooms will be lost, but the plant should still bloom in summer and fall.

Another cause of non-blooming of hydrangeas relates to the weather. Spring-blooming plants whose buds were developed the previous year may lose those buds with a late spring freeze.

As it warms in early spring, the flower buds expand with water and begin to soften and cause the buds to break. When this happens, they lose their cold tolerance and a late freeze may kill them. The reblooming hydrangeas also may lose their spring flowers with a late freeze but will still bloom later in the summer. That is why this type of hydrangea is popular in our area.

These are the main causes of hydrangeas not blooming, but there are others.

Most varieties need about four hours of sun to bloom. If a hydrangea is planted in full or mostly shade, it will have nice green leaves, grow tall but not bloom.

Another factor to consider is that these plants need time to develop root systems and develop height before they consider blooming. Some plants may take two or more years to do this, so if everything else seems optimal and the plant doesn’t bloom, give it more time.

A last possible cause relates to most all plants in the flower or vegetable garden. If you use too much nitrogen fertilizer, plants will grow tall and green and not flower.

Bigleaf hydrangea:  Examples of bigleaf hydrangea:  Let’s Dance®, Edgy®. Abracdabra® and Pink Shira®

Hortensia: an old-fashioned common name for mophead forms of Hydrangea macrophylla. It is also the French and the Spanish word for hydrangea.

Smooth hydrangea: Examples of smooth hydrangea: Invincibelle® Spirit II, Incrediball®, and White Dome®

Oakleaf hydrangea:  A North American native hydrangea with large, cone-like white flowers and large leaves that resemble those of the oak tree. It is widely known for its excellent autumn color and unusual peeling bark as well as for its showy blooms.

Panicle hydrangea: Examples of Panicle hydrangeas: ‘Limelight,’ Little Lime™, Quick Fire®, Pinky Winky™, ‘Little Lamb’ and Bobo™

Mountain hydrangea: Relatively new to North American gardeners, mountain hydrangea is much like bigleaf hydrangea in terms of its rich pink or blue flower colors and attractive, dark green foliage. Examples of mountain hydrangea: Tuff Stuff™ 

Compact hydrangeas: As with other plants, compact (sometimes seen as dwarf) hydrangeas are smaller versions of their bigger kin. Because they stay small, there is no temptation or need to prune them, eliminating the pruning errors that so often complicate hydrangeas. Examples of compact hydrangeas: Bobo™, Little Lime®, and ‘Little Lamb,’

Hydrangeas can be grown in containers. Like Quick Fire®, it is early blooming, flowering about a month before other hydrangeas. White flowers transform to pink-red as summer progresses. This dwarf plant fits easily into any landscape in container gardens. The white flowers turn pink in later summer and will grow at maturity to 36 inches in a container. This is a panicle type of hydrangea. Purchase the dwarf variety for your patio or container.

Another very hardy reblooming hydrangea is Lacy pink flowers reblooming mountain hydrangea called Tough Stuff and only grows to 24 inches. The flowers are blue-purple in acidic soils, pink in basic soil.

We planted the BoBo® hydrangeas at the Kent Feed sign on the Muscatine County Fairgrounds. It is a dwarf panicle with abundant white summer flowers that turn pink in autumn. These hydrangeas bloom every year.

Consider purchasing a hydrangea for your landscape. There are many colors, shapes and sizes that will fit your yard, patio or pot.
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