NEIGHBORHOOD GARDEN FOR MAY 2, 2015 *************************************************************

HYDRANGEAS PART #3

PRUNING AND FERTILIZING

BY GEORGE EDGAR

            If your Hydrangea blooms on new wood (this year’s new growth) cut back these shrubs all the way to the ground in late winter or early spring before new growth begins.  This includes Panicle hydrangea and Smooth hydrangea. They will grow and set buds the same year that they bloom. Shrubs that flower on new wood generally start blooming later than old-growth bloomers, beginning in midsummer and continuing until the first frost.  These shrubs are forgiving if pruning is not done at a certain time as long as you avoid pruning when the flower buds are opening.

          Some branches of new wood flowering hydrangeas often fall over under the weight of their blooms. One way to alleviate this flopping is to cut the stems to a height of 18 to 24 inches instead of clear to the ground in order to provide a sturdy framework to support the new growth. A framework like a peony ring also works.

          When pruning your Hydrangea that blooms on old wood (last year’s growth) PRUNE AFTER BLOOMS FADE!!! This includes Bigleaf hydrangea (Hydrangea macrophylla), Hydrangea serrata, and Oakleaf hydrangeas (Hydrangea quercifolia). To determine if your hydrangea blooms on old wood (last year’s growth), think about when it flowers. Generally shrubs that bloom before July 1st are considered to bloom on old wood.  These shrubs form next years flower buds in late summer or early fall as the days get shorter and temperatures cool off. To reduce the risk of removing these buds, prune just after the flowers begin to fade. Pruning other than right after blooming removes all of next year’s flower buds. Often, the earlier you get it done after bloom, the quicker the shrub can recover, producing more and larger blooms next season. When you do prune Hydrangeas that bloom on old wood, just snip off spent blooms just below the flower head and remove any wayward, straggly, or dead canes at the soil line.

          If you are not sure what kind of Hydrangea you have, cut off a 12 to 14 inch cane (with leaves and preferably a flower) and take it to a full service garden center or your local County Extension Office for identification. He/she will want to know if it flowers before July 1st or after July 1st, how tall the plant is, and what the flower looks like. A digital picture really helps.

          He/she can then tell you what family the Hydrangea belongs to but probably not the specific cultivar, and can instruct you on when and how to prune, best location in your landscape, and when to fertilize.

          Many Hydrangeas will do fine in our soil but they prefer a slightly more acidic soil than the 6.5 to 7.5 pH that we have in Eastern and Central Nebraska. Some hydrangea species will develop blue flowers. Aluminum is what turns the flower blue. Most of our soils have enough aluminum to turn the flower blue if the pH is low enough (4.7 to 6.0). Too much aluminum can be toxic to many plants including Hydrangeas. Therefore, Gladys and I use granular horticultural sulphur rather than Aluminum Sulphate. Or you can apply “Holly Tone” which has both a slow release fertilizer and granular sulfur. When planting a Hydrangea that has blue flowers, I put lots (up to one-third maximum) of Canadian Peat Moss (which is acidic) in the soil and at least one cup of granular sulphur per plant. Then at least every spring and many times in the fall I put a cup of granular horticultural sulphur around each acid loving plant.

                   In regard to fertilization, Dr. Michael A. Dirr, Professor of Horticulture at the University of Georgia, and recognized international expert on trees, and shrubs, recommends application of a 10-10-10 slow release granular fertilizer. He recommends application of a small amount of this slow release fertilizer scattered around the base of the plant and outward in early spring as the plant is leafing out and then another application after flowering.    

          Liquid fertilizers like Miracle Gro or Miracid are effective but most are not slow release and provide more rapid greening, so must be applied more often. Miracid by its self does have enough sulphur to accomplish what you need to lower the pH, but only if you apply it every time you water. There is a danger here in doing this as you may apply too much nitrogen. Remember that one of the reasons some plants do not bloom is because they get too much nitrogen fertilizer in relation to the phosphorous. Nitrogen makes your foliage grow but it is the phosphorous that is needed to produce flowers.

          Dr. Dirr also recommends that you not fertilize any tree or shrub after the middle of August. A fertilizer at this time of year stimulates growth that will probably not mature and thus will winter kill. Your plant needs to start getting ready for winter and not put on new growth. You may think you are doing your plant a favor by giving it a good shot before winter, but you may be doing more harm than good.

Many people driving around see what they call a “Snowball Bush”. It may be a Smooth hydrangea (Hydrangea arborescens ‘Annabelle’ or the new ‘Incrediball’) with creamy white flowers a foot across. It also maybe a “Snowball Viburnum” (Viburnum opulus ‘Roseum’). ‘Roseum’ will take full sun whereas ‘Annabelle’ likes partial shade. Another example why you need to find out about your plant and keep the tag so you know when to fertilize, how to prune, and does it need sun or shade. Common names can be deceiving.

There is a new pink Hydrangea arborescens on the market called “Bella Anna”. I have not seen it in Lincoln but check with your local full service garden center or you may have to order it on line.   

RESOURCES:

·        “Hydrangeas for the American Gardens” by Michael A. Dirr, (Timber Press: Portland) 2004

·        “Hardy Hydrangeas” by Cindy Haynes, Department of Horticulture, Iowa           State University, Horticulture and Home Pest News for June 22, 2001 (www.ipm.iastate.edu/ipm/hortnews)

·        HydrangeasPlus.com newsletter (Hydrangeas Plus: A division of VanHoose Enterprises, LLC, and P.O Box 389, Aurora, OR 97002)

·        Hydrangea. COM (Wilkerson Mill Garden, Palmetto, GA 30268)

·        “Pruning Hydrangeas”, Fine Gardening Magazine, The Taunton Press: Newtown, CT 06470-5506, May-June 2007, pages 51-53.

Copyright 2015