There are a number of different varieties of Hydrangea shrubs that are often grown into tree form. Many people don’t realize that a Tree Hydrangea is actually a Hydrangea shrub that was simply trained to grow as a flowering tree. This is also done with Rose of Sharon, I’ve seen it done with Red Twig Dogwood, a number of different viburnums and even Wisteria can be trained to grow as ornamental trees.
The steps to do this are as follows and there’s also a video on this page as well.
In this example I am using a variegated weigela that we just potted up as an example because . . . it’s what I had handy to write this article. And this plant is a good example of what you are typically starting with when you train a flowering shrub into tree form.
This plant doesn’t look like it would make a nice tree because it has side branches and it has a serious case of “double leader”. Two stems each competing to grow upright as the main stem of the plant. To grow this plant into a single stem flowering tree do the following;
1. Remove one of those double leaders. In this example they are about equal so which one you remove doesn’t matter. But at this point remove one and also remove that little stub that at one time was the leader but it was either pruned off or it died back.
2. At this point I would only make those two cuts because we need those other side branches to make leaves and feed this plant through photosynthesis until the main leader puts on new growth and leaves. As that happens and the tree has plenty of leaves coming off the main leader you can remove those lower branches that will eventually detract from the tree.
3. Never allow any branches that need to be remove get larger than 3/8 of an inch in diameter. Ideally remove them when they are 1/4″ or about as thick as a pencil.
4. Using some kind of a plant stake, bamboo or other wise, stake up the main leader and secure it to the stake so it grows nice and straight. I often use duct tape for this because when the tape is out in the sun it only holds up for about 12 months before the glue dries and the tape falls off. Other tape might not come off as easily and it will eventually damage the tree.
5. Allow the main leader to grow straight as a single stem. If the main leader produces side shoots they will eventually have to be removed, but keep in mind that the tree needs lots of leaves in the early stages so you may want to leave those side shoots temporarily.
6. Early next spring you need to cut the top off of the main leader at the point where you want the branching to begin. Usually about 30 to 36 inches off the ground is ideal. Just snip the top off.
7. The snipping off the terminal bud will force the plant to start putting out lateral branches right below where you make that cut. Those branches will develop into the head of the tree.
8. As the branches that will make up the head of the tree start to develop and produce lots of leaves, you can remove all of the growth (side branches) from the ground to the point where the head of the tree starts.
9. As the head of the tree grows it’s important to do some trimming so the head grows nice and full and not lanky. In the video you can see where the trees I am using as examples were trimmed and how much the trees filled out after each pruning.
That’s it! That’s how you train flowering shrubs like P.G. Hydrangea into Tree Hydrangeas.
And here’s a new video on Growing Tree Hydrangeas.
You can easily propagate hydrangeas from cuttings. See this technique for doing them during the summer as softwood cuttings and this technique for doing them in the winter as hardwood cuttings.
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