All the colorful blooming plants you can see in a December garden

It’s December in Los Angeles, but if you just arrived here from Chicago or New York and have never been here before, you may be in shock when witnessing certain plants in full bloom. I saw some Iceberg rose bushes the other day that were completely covered in wedding white flowers. How ironic that Iceberg roses are blooming in December just as icicles, if not icebergs, are forming in colder climes. 

Then there is the hibiscus bush I noticed with an opulent display of yellow flowers as if we were in the midst of a Hawaiian spring. Sweet pea bush (Polygala x dalmaisiana) is another December bloomer. It’s a rangy plant that can grow six feet or taller and has a flower color that combines pink, magenta, and a dash of purple. It blooms from summer through fall and beyond. Cut it back to keep its form more compact, but planted on your property line, it does provide separation from neighbors’ yards. Sweet pea bush does best growing in full sun but it can handle a bit of shade. There is a dwarf version of this plant (Polygala fruticosa var. Petite Butterfly) that only grows three feet tall and keeps its more compact form. And then, of course, the staunch woody shrubs we call orange bells and yellow bells (Tecoma Stans varieties) are bursting with blooms, as is cigar plant (Cuphea ignea).

Another way to bring color into the December garden is to plant two ornamental grasses with pink flowers that bloom at this time of year. The first is pink muhly grass (Muhlenbergia capillaris). Its thin kinetic flower stalks offer a glistening, glittering pink display. Then there is ruby grass (Melinus nerviglumis), with thick flower heads in every shade of pink with occasional outbursts of ruby red. Both grasses are clumping but non-invasive in Southern California. While pink muhly grass rises to four feet tall, ruby grass is diminutive, with a height of around one foot. Both species are available from nurseries supplied by San Marcos Growers (smgrowers.com) and pink muhly may be ordered through retail outlets of El Nativo Growers. When you reach their website at elnativogrowers.com, click on “How to Buy” and then “retail locations” to find an outlet for their plants in your area. 

Trees, of course, are the plant kingdom’s classic purveyors of fall color. Each year during December, I witness the foliage of several ginkgos in my neighborhood turn gold. Other commonly seen local trees with golden foliage include honey locust (Gleditsia triacanthos) and Lombardy poplar (Populus nigra Italica). Chinese tallow tree (Sapium sebiferum) is a mixed blessing. Although its foliage is unmatched for luminescent leaves in every version of yellow, orange, and red, and its mature height is a modest 40 feet, its roots can grow along the soil surface. In addition, its fruits are slippery so make sure not to plant it next to sidewalks or paved surfaces where people walk. Chinese flame tree (Koelreuteria bipinnata) is noteworthy for its unusual papery seed capsules that turn magenta at this time of year. Its large panicles of golden flowers bloom in the spring with a mild fragrance. 

Sweet gum (Liqauidambar styraciflua) displays all the classic fall colors in its leaves, whose shape closely resembles maple leaves. This species has a strong vertical growth habit but its downfall is highly invasive surface roots. Chinese pistachio (Pistacia chinensis) shows off brilliant red-orange leaves before dropping. This is an unmatched species for fall color and has a symmetrical domed canopy with a mature height in Southern California of 30-40 feet. The ubiquitous crepe myrtle may also show off colorful fall foliage but here it is best to examine specimens in the nursery before purchase because some crepe myrtles have more colorful fall foliage than others.

When it comes to shrubs with fall colors, evergreen members of the barberry genus steal the show. Japanese barberry (Berberis thunbergii) has multiple varieties with a mix of foliar colors that become more vivid as temperatures cool. Similarly, heavenly bamboo (Nandina domestic) has a fiery December presence, especially as seen on the foliage of its compact and dwarf varieties.

There are California natives that change color, too. Oregon grape (Mahonia aquifolium) is one and the Roger’s Red variety of California grape (Vitis californix) is another. Roger’s Red is a suitable candidate for covering a gazebo or arbor while the native California blackberry (Rubus ursinus) grows six feet tall and is suitable for disguising a chain link fence of a similar size. Pacific blackberry, in the manner of all blackberry species, has foliage that may turn yellow, orange, red, and purple at this time of year. Boston ivy (Parthenocissus tricuspidata), although native to East Asia, offers a memorable kaleidoscope of color when allow to grow up a wall. It is this plant, incidentally, from which the Ivy League got its name, due to its function in covering brick walls of colleges throughout the East.

Plant physiologists have determined that coloration of leaves depends on carotenoid and anthocyanin pigments. Carotenoids are always present in leaves but are invisible until fall when, with the collapse of green chlorophyll molecules, the yellow or gold pigments are revealed. During this same period, red and purple anthocyanin pigments are synthesized.

Red pigments in plants, including those on flowers, stems and fruits, act as a kind of sunscreen, blocking out harmful ultraviolet rays and, in general, reducing the impact of excessive light exposure. This is especially important when temperatures cool and cells are more susceptible to sun damage; to defend against this possibility, red anthocyanins are synthesized in autumn leaves.

California native of the week: Two California native trees have foliage that turns a vibrant gold at this time of year. One of them is velvet or Modesto ash (Fraxinus velutina var. Modesto). This tree has a beautiful natural form and you never want to prune it for this reason, especially since its mature height is only about 40 feet. It is susceptible to disease which seems to be more of a problem after the tree is pruned and is in a weakened condition. California black walnut (Juglans californica) is widely seen throughout the state and its golden leaves are currently on display before they drop. Its nuts are small but with an intense and pleasing flavor. There is no more drought-tolerant tree than California black walnut and it will not require irrigation one year after planting. Should it come up as a volunteer seedling, it will never need to be watered unless we are subject to a prolonged drought. California black walnut, due to its disease resistance, is used as a rootstock for most of the English walnut varieties that are planted in California. About 99% of commercial walnuts grown in the US are English walnuts grown in California. English walnut, however, is a misnomer since this nut is actually native to mountainous areas of central Asia and southeastern Europe.

Email Joshua@perfectplants.com with your gardening questions, comments and success stories.