Planting Mock Orange shrubs to make hedge
Your info says to trim annually. Would trimming more often (say 3 times a year) result in the shrubs growing thicker? I am concerned about how the roots grow, i.e. just under the surface of the ground or more down into the soil and how strong the root growth. Will it push against any near-by brick walls to the point of dislocating them? Ok to use hedge trimmers when pruning or use only hand shears? Thank you, David (Live in Hawaii)
Certified GKH Gardening Expert
Pruning more often could lead to lack of flowering.
Use the tool that works best for you and that cleaning makes pruning cuts. Tools should be clean.
In referring to "mock orange", there are several plant species that have this common name. So this is one case where it's best to clarify which one you are referring to in order to get the appropriate information. Botanical names can help.
You're in Hawaii, so I am wondering if you are referring to the native Hawaiian plant: Alahe’e (Psydrax odoratum), aka “Hawaiian Mock Orange”.
Or to one of the other mock oranges, including
Murraya paniculata, Pittosporum tobira, Pittosporum undulatum, and the common US mainland, southern Europe plant by that name, Philadelphus coronarius.
Since you referred to a Gardening Know How article, I will assume you saw the photos and recognized your plant as the Philadelphus that is discussed in the article.
I would stick with the annual pruning recommendation after flowering. Here's more: https://www.gardeningknowhow.com/ornamental/shrubs/mock-orange/mock-orange-pruning.htm
In order to enhance natural form and beauty as best possible, it's better to use hand shears and make individual reduction cuts. It's more time consuming, but more professional and leaves a more natural look than with hedge shears.
As far as invasive roots, I wouldn't worry too much about that with the smaller shrub forms like the Philadelphus. Most of the absorbing roots will be lateral roots in the top six inches of soil. Some structural oblique roots may go deeper. Even with shrubs like this that have primarily fibrous roots, it's best to provide plenty of soil space and don't plant too close to the brick wall. If you have the Pittosporum 'Mock orange", which are large woody shrubs and small trees, then root encroachment and dislodging of an un-reinforced brick planter or header is more likely.
To promote hedge density, concentrate on initial spacing of plants, soil fertility and water management.