Brrrrrrrrrrrrrrrrr its cold out there
Kind of brutal on skin and the tender leaves of sub-tropical and tropical plants. Although it hasn't dropped down below 20 degrees, which is when I really start to worry, we have had some seriously cold nights.
Things to cover when it gets down into those cold temps are small Citrus, Hibiscus, Bougainvillea, Orchids, tropical pond plants and landscape plants, Pelargoniums (Geraniums), Cuphea, Mandevilla, Tree Ferns, Brugmansia, succulents and tender new plantings. Many flowering vines are subtropicals i.e. Trumpet vines, Bower vine, Hardenbergia- anti-desiccant sprays (see below) would be good for these.
Use cloth not plastic sheets to cover the plants and if you can, support the sheets off the foliage to avoid frost burn. Remove the sheeting in the day if it is sunny out. For further warmth you can use a light or single bulb below the sheets- this actually works believe it or not. Avoid contact of sheet to bulb!
There are sprays that can also help such as "Wilt-pruf" and "Cloud Cover" which are anti-desiccants
that help to keep leaves from "freeze drying". Follow manufacturers specs. for application and re-spray after rains.
Keep plants well watered between sporadic rains as this helps the leaves of all plants from becoming to wilted in the frosty weather.
Many plants will have frost burned foliage and go dormant in the cold weather but will recover in the late spring or summer growing from the roots or base. Leave any damaged plants well into the warm weather to make sure that they are really lost before replacing them.
The best advice is to avoid the use of plants not suited to your climate zone. We are having a significant climate change so have had good luck with sub-tropical here but hard freezes are cyclical so they are bound to hit gardens at some point.
Enjoy the frost and snow in the mountains- a pretty sight for Christmas time.