The only bright spots I see are provided by two Tibouchina urvilleana (princess flower), 15-foot trees that brighten the garden with eye-catching, vase-shaped, brilliantly royal purple blossoms. These deeply colored blossoms held on terminal panicles above the foliage create a spectacular sight. Flowers open throughout the year, but are especially plentiful from May to January. Tibouchina urvilleana prefer well-drained soil until they are established but, as they are drought tolerant, will adapt to very dry soil. Flowering is best, however, if the tree receives full sun and is watered regularly.
My research for other winter-blooming trees hardy in our Mediterranean climate led me to Azara microphylla (boxleaf azara), an evergreen, shrubby tree that matures at about 15 feet. In late winter into early spring, it produces little fluffy yellow pompom flowers at the leaf axils that smell like chocolate to some people, vanilla to others. The dark green foliage is glossy and held tightly on spray-like branches for an airy effect. Its open habit and fine texture are very attractive in the shade garden. Azara microphylla is a narrow-growing tree, which grows best in part shade in well-drained soil.
For a significant addition of color, consider a Calliandra haematocephala (Calliandra inaequilaterai) or powderpuff, a native of Bolivia that grows to a height of 10 to 15 feet. The tree produces large, rounded, vase-shaped powderpuffs composed of watermelon red stamens from fall to early spring. Pinching the new growth increases the number of branches, which, in turn, produces more flowers on a more-compact, more-dense plant. The long, unbranched stems on this evergreen tree form a vase-shaped canopy suitable for creating some shade for a small patio. The tree tolerates drought and will grow in very dry soil, but prefers well-drained loamy, sandy or clay soil. A partially to fully sunny site produces a fast-growing tree, especially if supplied with regular watering while young. The tree serves as a host for statira sulfur (Phoebis statira) butterfly larvae.
A tree that gets attention through all seasons because of its thorny trunk is the Chorisia insignis (floss silk tree). Chorisia insignis is a deciduous tree in the Bombacaceae family, which reaches a height of 25 to 50 feet. Grafted trees are preferred as they bloom earlier and at a smaller size. Although most seedlings in California have thorny trunks studded with thick spines, some seedlings may be nearly thornless. The tree produces large showy blossoms that resemble narrow-petaled hibiscus blooms throughout the fall and winter, especially if the tree benefits from full sun. Flower color ranges from magenta to light pink, dark burgundy, creamy yellow or white with a yellow throat. Silk trees will thrive in any reasonably fertile soil with good drainage. Trees cast light shade under the canopy making it easier to grow turf under the tree than under other trees with a denser canopy. Chorisia insignis is known for its large seedpods, which contain notable amounts of a cottony fiber that has been used as stuffing in pillows and as insulation in parkas and other cold-weather clothing. The pollen from this tree may cause some people to have allergic symptoms.
Another beautiful tree that is valued for its flowers, fruit and foliage and provides all-year interest is Cercis occidentalis (Western redbud). The Western redbud is a relatively small, multitrunked tree with spreading branches and is native to California. The tree is one of the earliest flowering trees and is often used to add color to gardens. Clusters of small, sweet pea-shaped, rosy to purplish-pink blossoms appear in early spring along the outward-reaching stems, ultimately covering the branches in an explosion of color. In early summer, the branches are adorned with magenta seedpods. In the fall, the foliage turns bright yellow or red; bare branches holding reddish brown seedpods provide interest in winter. If you add the dangling heart-shaped leaves to this beautifully changing picture, you can understand why redbud trees are so popular as ornamental trees.
Other wonderful additions to the winter garden include Camellia sasanqua (Sasanqua camellia), which produces a plethora of lightly fragrant, white or pink flowers in autumn and early winter, or Mahonia lomariifolia with its clusters of yellow flowers in midwinter. Plants with colored stems - Cornus (dogwood) and Salix (willow) - provide bold splashes of color from November through early March.
The winter garden brings together colored stems, colored leaves and winter flowers with variations in texture and form. Together these specimens brighten the winter landscape and enchant the viewer, especially when the garden is flooded with the light of the winter sun.
The University of California Marin Master Gardeners are sponsored by UC Cooperative Extension.ÊFor questions about gardening, plant pests or diseases, call 499-4204 from 9 a.m. to noon, and 1 to 4 p.m. weekdays, or bring in samples or pictures to 1682 Novato Blvd., Suite 150B, Novato