Blue wave hydrangea and rose of Sharon doing horribly! - Knowledgebase Question

dudley, Ma
Question by sjlingner
July 9, 2007
Hi, I had Lanscapers plant two blue wave hydrangea and two rose of Sharon in my yard 3 years ago. They are right near a pond and my soil does tend to be a bit sandy. They were doing well for two years and seamed to be getting bigger. The Rose of Sharon bloomed for two years and the Hydreangea bloomed once (one bloom each) last year. This year, one of the Rose of Sharon looks dead and the other only has tiny leaves on it and it is July. The hydrangea are growing leaves out of the dead looking stocks but are WAY less developed than several others that I see around the pond and smaller and less developed that they were at this time last year. How do I help them?? Should I have pruned and if so when? What should I feed them if anything. Everyone else's look great so I know they can grow in my area. Please help!! I will do anything!!Thanks

Answer from NGA
July 9, 2007


Last winter's oscillating temperatures were very stressful on many plants and caused winter damage on many plants. Both of these are winter hardy into zone 5, and you are located at the edge of their hardiness, so a difficult winter could set them back badly. The hydrangea blooms on old wood, so excessive winter damage could prevent them from blooming. Spring frosts/freezes can also damage tender new growth and prevent blooming as a result.

Depending on your microclimate where they are planted, you may find that these hydrangeas do not bloom well (or at all) most years. A spot with protection from sweeping winter wind as well as avoiding a low spot (frost pocket) might be an important factor in how well they perform.

Hydrangeas also need a rich, organic soil that stays evenly moist yet is well drained. This means it should be damp like a wrung out sponge, not sopping wet and not dried out. Overly wet soil or dry soil would both cause poor growth.

This type of hydrangea is pruned in spring only to remove dead wood, then in summer if needed it can be thinned or lightly shaped after bloom.

The Hibiscus syriacus shrubs tend to suffer winter damage in cold winter climates such as yours and usually need to be pruned in the spring to cut off the winter killed branches. If necessary, they can be pruned a bit more to restore a symmetrical look. Early spring is the only time these should be pruned. They come into growth fairly late in the spring, but you should see vigorous growth by now. These shrubs bloom on the new growth of the season, so they go on to bloom later in the summer.

Rose of Sharon needs full sun all day long to bloom its best, it likes heat and sun. Average soil is fine, but it must have a well drained location. In a poorly drained spot it will be less winter hardy and will also sometimes suffer root problems.

Another issue that could be causing poor performance would be related to whether or not they are rooting into the soil as they should. If planted with encircling roots left intact rather than cut or untwined and directed outward, they could be suffering from constricted roots that have stayed in the original planting hole.

As far as fertilizing, an annual spring top dressing of compost along with a slow release granular fertilizer per the label directions should be adequate. Using an organic mulch year round will also help feed the soil slowly as it breaks down over time.

I hope this helps you trouble shoot.

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