Sweetshade (Hymenosporum flavum) has yellow flowers that fade quickly to white so that, when in full bloom, the tree appears to be covered in popcorn. Sweetshade is nearly always placed in a wind-protected location, or against a building, since its vertical growth habit and brittle branching structure cause it to break apart in stormy weather if planted in an open area. To create a stronger tree with a broad and wind-resistant canopy, pinch terminal shoots when it is young to encourage lateral growth.
Sweetshade, an Australian native which can easily withstand freezing temperatures, is also known as Queensland frangipani, since its flowers’ scent resembles that of common frangipani (plumeria). It is in the Pittosporum family and shares the lush green foliage of Victorian box (Pittosporum undulatum), a wonderful background tree suitable for a tall, informal hedge and mock orange (Pittosporum tobira), a tough evergreen shrub.
The purple orchid tree (Bauhinia variegata or purpurea) is hard to miss this time of year, even though its flowers seem to have more pink than purple in them. I have seen it grown as a street tree here and there in Southern California. It has a difficult time standing up straight and requires conscientious pruning to create a balanced specimen that can be relieved of stake support.
It produces large quantities of seed that germinate with ease. A fascinating example of this is visible in the greenway running along the south side of the Los Angeles River in the east Valley, where a small Bauhinia forest has sprung up.
Buahinia blakeana, the Hong Kong orchid tree, is a sterile, seedless species with larger flowers than those of the purple orchid but with less cold tolerance.
Robinia x ambigua ‘Purple Robe’, even without training, grows into a highly symmetrical specimen that is covered with a vivid mantle of reddish violet flowers in the spring.
‘Purple Robe’ is a leguminous tree that grows just fine in desert soil with little water. The related Idaho locust (Robinia x ambigua ‘Idahoensis’), with deep magenta pink flowers, may be observed growing in the Chandler Boulevard median in Sherman Oaks.
The fringe tree (Chionanthus) is slow but will eventually reach 20 feet in height. In its early years, you will think it nothing more than a tall shrub but, with patience and appropriate pruning, it will eventually be transformed into a tree. Its generous clusters of white-tasseled flowers are highly fragrant. An outstanding specimen grows just inside the entrance of the Descanso Gardens in La Canada.
As long as we are on the subject of large shrubs that turn into trees, I cannot help but mention the strawberry tree (Arbutus unedo). So-called because of its edible, if insipid, red fruit, the strawberry tree is suitable for nearly every type of soil and will grow anywhere in Southern California, including Palmdale and Lancaster, to a height and spread of 30 feet.
Cold weather is not a concern but it will grow best in our hot valleys when protected from afternoon sun.
If you are wondering about its flowers, which are visible in fall and winter, take a look at any currently flowering manzanita (Arctostaphylos), whose urn-shaped blooms are identical to those of the strawberry tree.
I was recently on Catalina Island and marveled at the large Pride of Madeira plantings adjacent to the landmark Casino building in Avalon. Pride of Madeira (Echium candicans) is probably the most ostentatious spring bloomer. It is a perennial with thick, giant flower spires which may appear in lilac, mauve, or any shade of blue.
Although individual plants only live for a few years, seedlings come up readily and clonal propagation may be achieved by detaching four inch shoot tip cuttings, dipping them in root hormone, and inserting them into fast-draining soil or into an artificial mix consisting of two parts sand or perlite and one part peat moss.