The houseplants that might have been placed in the garden to get rinsed by the rain should have already been brought back indoors. Even before actual frost, some houseplants may be distressed by prolonged exposure to cool weather, particularly since most are tropical or subtropical. Those that have grown in shade within the home for a long time may also be sensitive to direct sun exposure, even though daytime temperatures remain rather cool and sunlight intensity is diminished even during the clearest of winter weather. (The sun is lower on the horizon, so sunlight is diminished as it passed through more of the atmosphere. Duration of daylight is also diminished.)

The most effective method of frost protection is to simply not grow anything that is very sensitive to frost. If this technique is too restrictive, frost-sensitive species should be grown in portable containers or located where they are sheltered from frost by the canopies of larger trees or architectural features, such as lanais, eaves or carports. Sensitive species that must be grown in exposed (unsheltered) soil will unfortunately require protection from frost.

Potted or tubbed tropical plants can be moved to sheltered locations prior to a freeze and then returned to their original locations, or can simply be relocated for the winter. Because most are somewhat dormant and inactive during winter, there is not much advantage to returning them to optimum locations until weather warms in spring, ending the threat of frost and initiating resumption of vascular activity. Temporary relocation is so brief that the sheltered location does not need to be luxurious, but a seasonal relocation site should be comfortable enough to sustain frost sensitive guests through winter.

Larger "uncontainerized" specimens or even smaller plants grown directly in the garden soil can be protected by simple tent-like structures that slightly but effectively disrupt radiation of heat during the night. Vinyl or fabric (such as burlap) should be suspended by simple frames of bamboo, stakes or even pruning scraps (branches), so that condensation on the covering material can not touch and freeze onto the foliage below. Cardboard, newspaper or even scraps of carpet or vinyl flooring are useful for small plants. The protected plants will be much more comfortable if coverings are removed every morning. Opaque coverings obstruct sunlight, and clear vinyl retains too much heat when exposed to sunlight.

As unsightly as frost damage is, it should not be removed from damaged plants until spring, as it will help to insulate undamaged tissue below. Premature removal will only stimulate emergence of new growth, which will be even more sensitive to frost. I actually prefer to allow my geraniums to freeze and do not disturb them until I prune them back hard in spring. I find that protection is too much work and is as unsightly as the damage it is intended to prevent.

Vine of the Week:
Grape ivy

Grape ivy, Cissus rhombifolia, can be grown in gardens of the Santa Clara Valley if protected from frost, but is almost exclusively grown as a houseplant. There are so many more resilient vines for the garden, but not much that is comparable to it indoors. Like related grape, it climbs with tendrils and may eventually get 20 feet high, but it usually sprawls or hangs from hanging pots as a houseplant. Grape ivy is not discriminating about sun exposure and will be happy with full sun or considerable shade.

The dark green leaves are divided into three slightly serrate, two- or three-inch long leaflets. Reddish tomentum (fuzz) may seem dusty, particularly among young foliage. At least two cultivars and some of the others species of Cissus that may be marketed as grape ivy all exhibit distinct foliar variation. Flowers are almost never seen.

Horticulturist Tony Tomeo can be contacted at 408.358.2574 or at LGHORTICULTURE@aol.com.