NOVEMBER 26, 2008
SO, HOW DO I PRUNE MY HYDRANGEA?
You will recall that a few weeks back I offered some sage advice on how to prune. I covered the basics which included the two main types of pruning cuts and a little bit of information on timing. Then I left you hanging on hydrangeas. So here is the rest of the story with a very brief review of the basics.
There are only two kinds of cuts in the pruning world: thinning cuts and heading back cuts. A heading back cut is where you cut off the end of a branch or stem. Doing this causes lots of branching and growth right below the cut. A thinning cut is where you completely remove a branch down to where it is attached to another branch. Thinning cuts are much less traumatic and donít cause the rampant re-growth that heading back cuts do.
By combining these two types of cuts you should be able to accomplish your pruning goal no matter what kind of plant you are dealing with. If you need to stimulate more growth then you will use a heading back cut. Conversely, if you need to reduce the size or mass of a plant you will use a thinning cut.
In addition to understanding how a plant reacts to either a heading back or thinning cut, knowing when to prune is also important. Generally speaking, if a plant blooms early in the spring before it starts growing new foliage then you should prune it right after it finishes blooming. If on the other hand your plant blooms in the summer on the ends of the new growth then you should prune it at the beginning of the season before it starts to put on new growth.
All of this should make sense to us. But as with all rules, there are always the exceptions and this is where Hydrangeas come into the picture. Actually, there are several shrubs that follow the Hydrangea scenario. Weigela, Mock Orange and Deutzia are three that come to mind. What is it about these plants that confuses us? Let me explain.
These shrubs generally bloom in June after they have put on some new growth. At first glance we might assume that they are blooming on new wood just like a rose and follow the same pruning regime of being cut back hard in the spring. But in reality the flower buds were formed on last yearís growth along the upper portions of those stems. If we were to prune our hydrangea hard in the spring it would have the effect of removing most of the potential flowers for the season.
It helps me to think of a blackberry vine that grows a cane the first year and then flowers and produces fruit on that cane second year. While it is producing fruit on the one year old cane the plant is also growing new canes that will do the same thing the following year. So it is with most hydrangeas. At any one time you should have old canes that are blooming and new canes that will bloom the following year.
But unlike blackberry vines where once the cane has bloomed and produced fruit you should cut it to the ground, year old canes on a hydrangea will bloom again the next season as long as you donít cut them down too far. My rule of thumb is to just remove the old flowers and no more than a few inches of the cane. By doing this you should get more flowers the following season on that same cane and at the same time additional flowers on the new canes that grew the previous season. Have I got you totally confused yet?
Finally, to keep your hydrangea in a state of vigor you will occasionally need to completely remove (as in cut to the ground) some of the older canes which will have the effect of stimulating new growth at the base of the plant. If this pruning is done in early spring then the new growth that is generated should set flower buds and bloom the following season.
If you are following these techniques and your hydrangea is still not blooming then it is either in too much shade or receiving too much TLC. Move it to a sunny location (morning sun is best but they will tolerate full sun), cut back on the water but donít let it wilt and stop the fertilizer applications around July. If this doesnít work then I would threaten to dig it up and give it to your mother-in-law. This seems to work every time for me.
Steve Smith is owner of Sunnyside Nursery in Marysville and can be reached at the nursery at 425-334-2002 or email at email@example.com