Perhaps I’ve said it before, but it’s extremely helpful when you know what a plant’s growth habit is before you prune. Growth habit is basically the shape a plant naturally wants to grow into and how the branching structure supports that shape. For example: Arborvitae ‘Green Giant’ is pyramidal in form and proportionately much taller than wide. As a matter of fact, this plant will easily get to 30′ tall and 15′ wide in thirty years. Rapid grower…I think so. Its branching structure is horizontal with some ascending branches as well.
Other characteristics about the plant can be helpful too when deciding your pruning strategy. For instance, Arborvitae ‘Green Giant’ prefers more light (full sun is ideal). The less light it gets the thinner and more open its branching and foliage will be. Prune less aggressively if you know the plant is adapting to less than ideal conditions.
The Pruning Strategy
Let’s assume the ‘Green Giant’ you’re going to prune has been positioned to have enough room to grow and stay somewhat within its “natural boundaries”. If the space is too limited and there’s no future for the plant in that spot, think about transplanting it.
To give ‘Green Giant’ a strong trunk and branching structure, it’s important to prune them in their early years. In the first picture above, these Arbs were undoubtedly pruned early on in their lives. Notice how full they are from the ground to about 4/5ths of their height. However, the last growth at the top is thin and “stretched-out”. This is very typical of rapid-growth plants.
It is this top growth (upper 1/5th) that needs pruning. You should also scout the lower portion of the plant for any branch ends that may have grown more aggressively than others. There should not be many.
I apologize for the picture quality of these “before” and “after” shots, but even the silhouette conveys the degree of pruning I did.
I used a traditional trimming shear along with an orchard ladder. By today’s standards you might call that “old school”. I still think a good quality hand shear gives the best cut and, of course, with total control. I did, however, think how convenient and productive a telescopic gas powered shear would have been. Just take care as those power shears can cut aggressively.
The main goal and concept here is to trim the ends of the longer, fast growing branches to shape the plant and encourage fuller growth.
This is what plant nurseries do while they’re growing the plants for market. You want to continue this trimming routine for as long as it is practical. The idea is to develop a full, nicely shaped plant so that it can continue to grow on its own with this strong foundation you’ve help create.