California is a bit of a gardener's paradise. Especially in those areas of the state with mild winters, gardening can be a year-round endeavor. California has many microclimates: the coastal areas to the inland valleys and the cold northern regions to the desert-like south. Whichever microclimate you live in, there are many perennial plants that will thrive in the California garden and bloom all year.
In many areas of the U.S., the petunia is treated as an annual. It is actually a perennial that will bloom year-round in many parts of California. It does tend to get a bit sparse and leggy during the heat of summer. When that happens, just cut it way back, to about 2 inches, and it will grow back bushier than ever and soon bloom again.
Also known as Indian Mallow (its botanical name is Abutilon striatum), Flowering maple is not a true maple and is in fact related to the hibiscus. Its hibiscus-like, bell-shaped flowers bloom all year in the milder areas of California so long as you give it partial shade and rich soil. Most flowering maples suffer from mosaic virus that does not harm the plants but will show up as mottled leaves when the plant is grown in the sun.
This ivy-leaved geranium does especially well in coastal areas, blooming in pink, white and dark purple. Deadheading (pinching off fading flowers at the base of the stem) will encourage year-round flowering. This plant needs sun in the morning and some shade in the afternoon and protection from the wind.