I have two Hydrangeas growing up the side of my house in a northeastern exposure. This will be their 4th year. Leaf growth is robust… flower growth almost non-existent (on one of the shrubs, one bloom last year; one forming this year). What can I do to encourage bloom or should I start over?
According to the Plant Addicts website, there could be several reasons why yours are not blooming well. Check out their page, “Why Won’t My Hydrangeas Bloom?”
There is another useful resource that may be of help. Try Why Plants Fail to Bloom, by Leonard P. Perry, a professor at the University of Vermont Extension. Perry suggests there are five possible reasons: Age, Temperature, Alternate Flowering, Light, Nutrition and Pruning.
In addition, I consulted two books on hydrangeas. Both mentioned that Hydrangea anomala subsp. petiolaris can take time to bloom. According to Michael A. Dirr’s Hydrangeas for American Gardens, Time is [the climbing hydrangea’s] biggest ally. That is, once it gets established, there is no stopping it.
Michael A Dirr. Hydrangeas for American Gardens. Timber Press, 2004. p. 24.
Toni Lawson-Hall’s Hydrangeas: A Gardener’s Guide also says that Hydrangea anomala subsp. petiolaris “grows well on north-facing walls but takes a while to get established.”
Toni Lawson-Hall. Hydrangeas: A Gardener’s Guide. 1995. p. 81.
You are probably wondering how long a while is. Alas, I was unable to locate a specific timeframe for when you might expect those gorgeous blooms to start, but from what I can gather, time may help.