Non-Blooming Hydrangeas

Weather, pruning may be cause of non-blooming hydrangea

Bill Sevier, Ask a Master Gardener

Saturday, January 28, 2017

Q: I planted some mophead hydrangeas I bought from a local nursery, and they are not blooming. What could cause this? Amy, Tulsa.

A: The short answer is that the non-blooming is most likely related to pruning or weather issues, although there are other causes.

The Tulsa Master Gardeners maintain a helpline at the OSU Extension Office on 15th Street, and this is certainly in the top 10 questions called in during the growing season.

There are 23 different species of hydrangeas and five are cultivated in the U.S. These are smooth, panicle, bigleaf (mophead, lacecap), oakleaf and climbing hydrangeas, and they all share some, but not all, of the flowering habits of your hydrangeas.

In regards to blooming, the mopheads come in two general varieties. The older classic ones that just bloom in spring and the newer remontant (reblooming) varieties that bloom in spring into fall. The spring bloomers form flowers on buds developed during the previous late summer and fall. 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 (bud break). As they do this, 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 the northern states.

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.

For a helpful review of hydrangeas and their problems, the Proven Winner website is worth reading.

Garden tips

•        Begin planting blackberries, raspberries, strawberries, grapes, asparagus and other perennial garden crops in February.

•        One can continue in the month of February spot-spraying weeds in your dormant Bermuda lawn. Use a product containing glyphosate, found in Roundup and others. Use when the temperature is above 50 degrees and always read the label carefully before using.

•        Tomato seeds are best planted into indoor flats around Valentine's Day for mid-April garden transplants. Should you decide to grow your own tomato transplants from seeds, consult OSU fact sheet “Growing Tomatoes in the Home Garden,” which can be found on the Tulsa Master Gardener website. In that same section of the website, you will find additional fact sheets on growing conditions, pests and diseases, which are helpful.