UNITED STATES—This really is the best climate for gardening. Even though summers are mild, there are not many plants that want for more warmth. Even though winters are mild, it gets just cool enough for many plants that require winter chilling. Yet, there are a few plants, particularly plants from tropical climates, that can be damaged by frost. The best way to protect such plants from frost is to not grow them.
Of course, this oversimplified technique would prevent the cultivation of familiar plants like banana, angel wing begonia and angel’s trumpet. In cooler regions, it might involve bougainvillea, philodendron and some types of citrus. Most of us would prefer to take some degree of risk to grow marginal plants. Some may get damaged by frost and then recover. Others may be killed by frost.
Potted plants can be moved to sheltered spots when threatened by frost. Some can be brought into the home or garage temporarily. For some, the simple shelter of a porch or a dense evergreen tree might be sufficient. Bougainvillea and other plants that do not like to be potted might prefer to be planted under the eaves against a warm south-facing wall. A bit of warmth radiates from walls at night.
During the coldest nights, some of the most sensitive plants that can not be moved to shelter may need shelter brought to them. Burlap, plastic, paper or any sort of sheeting that can be temporarily suspended on stakes above the foliage should be sufficient. Leaves that touch the sheeting can potentially get frozen. The sheeting should be removed during the day so that it does not get too warm in the sunlight.
Foliage that does get damaged by frost should not be pruned away immediately. It may be unsightly, but if left for later, it helps to insulate inner foliage and stems from subsequent damage from later frost. Besides, immediate pruning stimulates new growth that will be even more sensitive to frost than was the foliage and stems that had already been damaged.
Highlight: ornamental grape
Boston ivy is not really ivy at all; but is more closely related to grape. Along with creeping fig, it is one of the two best vines for freeway sound-walls. It protects the walls from graffiti and muffles sound. Unlike creeping fig, which is evergreen, Boston ivy is surprisingly colorful through autumn. Unfortunately, it clings to whatever it climbs with holdfast discs, so ruins paint, stucco, and any other surface it gets a hold of.
Then there is ornamental grape, Vitis vinifera. It is about as colorful as Boston ivy, and can climb almost as aggressively to thirty feet, but lacks the damaging holdfast discs. It is nearly fruitless, which may seem like a waste of an otherwise perfectly good grape vine; but it will not make much of a mess until it defoliates. If any of the tiny fruit actually matures, it will almost certainly get eaten by birds before anyone notices.
Since it does not grip so tightly to what it climbs, ornamental grape can get rather shrubby. Outer growth can overwhelm and shade out inner growth, and can eventually produce a thicket of dead canes. Pruning back superfluous shrubby growth while bare in winter promotes more vigorous new growth the following spring and summer. Ornamental grape likes full sun exposure.