Why these water-holding trees are good choices for dry-climate gardens
Joshua Siskin writes about gardening in Southern California.
I have always had an affection for kurrajong trees. This could be on account of their suberized trunks, distinctive foliage, bell-shaped flowers with scalloped edges, or tightly arranged seeds, ensconced in woody follicles, which look like they belong on an ear of corn.
Kurrajong is the Aboriginal word for fishing line which may be produced from the fibers of its trunk. The botanical genus name given to these trees is Brachychiton, a combination of Greek words meaning short (brachys) and tunic (chiton), in reference to the coats that cover their seeds. These seeds are commonly eaten after being roasted.
Several kurrajongs are known as bottle trees but the one that stands out is the Queensland bottle tree (Brachychiton rupestris). The trunk of this species does resemble a bottle in its early years; it becomes bulbous or barrel-shaped at 7-10 years of age with its mid-trunk bulge eventually reaching a diameter of up to 11 feet, even while the tree in a dry climate like ours is unlikely to reach for than 30 feet in height.
The trunk resembles a bottle not only when young but throughout its life when you take its water-holding capacity into account. You can uproot this species and leave it alone for three months without worrying about desiccation. Transplant it following such a significant pause of root contact with the earth and it will soon show signs of new growth. During periods of drought, it becomes summer deciduous, dropping its leaves during this season. The species name of rupestris refers to rocks and indicates its ability to grow in rocky soil of inferior drainage. Its comely narrow leaves, evoking willow tree foliage, offer a refined contrast to the bulky look of its trunk.
The more common, if less dramatic, bottle tree has leaves similar to those on a poplar tree; hence its botanical name of Brachychiton populneus. This species is widely planted as a street tree because of its columnar growth habit and roots that grow straight down and are not a threat to lifting sidewalks. Australian flame tree (Brachychiton acerifolius) has generous panicles of flowers whose vivid scarlet color is not seen on the blooms of any other tree. Finally, lacebark or pink flame tree (Brachichyton discolor) is notable for its large clusters of salmon pink flowers.
You can find all four trees mentioned above in the Australia section of the Los Angeles County Arboretum in Arcadia.
Bottle trees are in the hibiscus family (Malvaceae), which includes several other notable trees. One is the baobab, made famous in the children’s literature classic, “The Little Prince.” Another is the cacao tree (Theobroma cacao), from whose so-called beans (which are actually seeds) chocolate is made.
The best-known ornamental tree in this family is the floss silk or kapok (Ceiba/Chorisia speciosa). For most of the year, this outlandish tree from Brazil is noticed primarily for its unique trunk that is covered with suberous, pea-green bark and large, squat, keep-your-distance thorns. These thorns keep Amazonian animals, especially monkeys, from chewing on the trunks. Thorns also collect dew that condenses into water and runs along the thorns to their pointed ends from where it drips onto the soil below, a useful strategy for self-irrigation in the event of a prolonged dry spell.
A silk tree’s starry, orchid blooms in late summer are followed by football-sized fruits. Soon, these fruits split open to reveal fluffy, silky fibers known as kapok that can be used as stuffing for pillows and seat cushions.
Until the 1950s and the advent of synthetic fibers, kapok — which is extremely lightweight and highly hydrophobic — was the exclusive material used for filling life preservers. It also served as padding in the upholstery of every automobile made in the U.S.A. Entire plantations of floss silk trees in East Asia were cultivated for kapok production.
Floss silk trees are deciduous and conveniently lose their leaves just before blooming. In their rainforest habitat, the loss of foliage eases access to their flowers by pollinating bats. Floss silk seeds stick to kapok fibers to assist in seed dissemination over long distances. Kapok’s buoyancy and water-repellent properties explain the fact that floss silk trees have naturalized in West Africa, their seed-embedded fibers having floated all the way there, across the ocean, from South America. Although the tree can put on massive growth and reach a height of 60 feet, Pink Princess is a dwarf cultivar that grows only 12 feet tall.
California native of the week: Island tree mallow (Lavatera assurgentiflora), a member of the hibiscus family, has the most explosive growth of any California native. Indigenous to Santa Catalina and Santa Barbara islands, it makes a quick hedge screen. Plant a seed in the fall in full sun and the seedling that sprouts from it will sky up to 10 feet tall within a year. It blooms on and off throughout the year but flowers most heavily in spring and summer. Flowers are dark pink to lavender pinwheels with white stripes on each petal. Maple leaf-looking foliage is dull green to vibrant green, depending on microclimate, watering regime, and season. California tree mallow is structurally weak and its branches will break as it ages unless it is regularly pruned. This plant is available at Tree of Life Nursery (californianativeplants.com) in San Juan Capistrano.
Please send questions and comments as well as gardening predicaments and successes to Joshua@perfectplants.com. If you have an unusual or exotic plant that most people might not know about or have an original approach to growing a familiar plant, you are invited to share your experience here.