A Gardening Journal
Today in the Garden of a Lifetime: Hardy Orange, Hardy Indeed
- Published: March 14 2015
The wide shot of the magnolia espalier in the March 10 post was only possible with my twelve-foot stepladder. Otherwise, the huge cake-stand topiary of hardy orange would have been in the way. In the shot below, the camera hadn't yet cleared the top branch of the topiary, which I had tied to a stake just last Fall as part of its training as the topiary's newest, highest layer.
The ball-in-training will only form if that top twig survived. The Winter was historic in its severity—and the topmost twigs of woody plants are most susceptible to damage. How did this one do?
Great! Even at a closer look, below, no winterkill is visible.
This seems all the more impressive in that this species itself isn't thought to be hardy colder than Zone 6, and this Winter has brought some temperatures below zero Fahrenheit, as well as weeks in a row when the temperature never rose above freezing. A woody plant's youngest twigs are also its most slender—and, usually, also its outer and, therefore, most exposed growth. They are the most vulnerable to desiccation from sustained dry and cold wind, and from freezes deep enough to cause cell rupture. And because they are the farthest away from the plant's roots, they are the most difficult to resupply with groundwater, especially when the ground itself might be frozen.
The picture below shows the full-length of this topiary of Poncirus trifoliata. (Here's how unkempt it was before its late-December pruning.) The freshly-staked young twig was this tree's most at-risk branch—and yet it's unscathed.
Provided its roots experience reasonable drainage in Winter, and the tree is sited in plenty of heat and sun so that its new growth can ripen fully in Summer and Fall, Poncirus trifoliata is probably hardy to Zone 6 at any age and size. But younger individuals can show some tip dieback after a rough Winter. At almost twenty-five years old, this specimen has always enjoyed full sun, rich soil, and decent drainage. No surprise, then, that its roots are wide spreading and deep, its trunk and limbs are thick—and it's displaying maximal hardiness.
Here's how to grow hardy orange. The pruning strategies I recommend in the link maximize the amount of time in each year that the shrub has a tidy shape—but also mean that the best show of flowers and fruit will be every other year.