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EUCALYPTUS


311


Eucalyptus Myrtaceae


EVERGREEN TREES AND SHRUBS


ZZONES 5, 6, 8–24; H1, H2 (SEE HARDINESS IN ENTRIES)


FFULL SUN


N LITTLE OR NO WATER, EXCEPT AS NOTED


litter that is also quite fl amma- ble. Do not plant eucalypts near homes or other fl ammable structures. Also pay attention to plant size; many species are best suited to larger properties. A few species grow as much as 10 ft. annually in their early years. Such a growth rate is typically associated with short- lived trees, but not in this case—fast-growing tree euca- lypts can live for at least a cen- tury if given proper care from the start. Occasional deep or prolonged freezes may kill even large eucalyptus trees. Don’t be too quick to remove them; they can sprout new growth from trunk or large branches, though heavy freeze damage may alter their appearance.


Eucalyptus polyanthemos


Impressive plants native to Aus- tralia. They range from sprawl- ing shrubs (many bearing the common name “mallee”) to sky- line trees. They are the most widely planted nonnative trees in California and Arizona, where they’ve been used for wind- breaks, shade, fi rewood, and hardwood timber.


Eucalypts are appealing on


several levels: Depending on the species, they may have attractive form, striking bark, good-looking foliage, or some combination of these features. Most have two conspicuously different kinds of foliage: soft, variously shaped juvenile leaves, found on seedlings, sap- lings, and new branches that grow from stumps; and (typi- cally) tougher adult or mature leaves. Almost all leaves, juve- nile and adult, have a distinc- tive pungent aroma, though some must be crushed to release it. Most eucalypts have small, inconspicuous white fl ow- ers followed by small, woody seed capsules; exceptions are noted in the text. Although they were popular landscape trees through much of the latter part of the 20th century, serious pest problems and smaller lot sizes have less- ened their popularity, especially in California. In addition, they contain highly combustible oil, and many drop considerable


Some botanists now divide Eucalyptus into several genera, with many of the plants listed here assigned to Symphyomyr- tus. Other new names are listed in parentheses. E. cinerea. SILVER DOLLAR TREE. Hardy to 14°F to 17°F (–10°C to –8°C). Grows 20– 50 ft. tall and 20–40 ft. wide. Juvenile leaves are gray-green, roundish to heart-shaped. Mature leaves are long, narrow, and mid-green. Cut back often for a supply of decorative juve- nile foliage, which lasts well in cut or dried arrangements. With- stands wind; grows best in a dry site or one with fast drain- age. Can be used as a peren- nial in borderline climates. E. citriodora (Corymbia


citriodora). LEMON-SCENTED GUM. Hardy to 24°F to 28°F (–4°C to –2°C). A stately tree to 45–90 ft. tall, 15–45 ft. wide, or considerably larger with great age. Mature leaves are golden green and powerfully lemon scented. Bark is smooth and powdery white, sometimes with a blush of pink or blue. An attractive, narrow tree that can be grown close to walls and walks, as the lower half to two- thirds of the tree is bare trunk. Stake young trees, as trunk is weak. Cut back and thin often to strengthen. Can take much or little water. E. cladocalyx. SUGAR GUM. Hardy to 23°F to 28°F (–5°C to –2°C). Growing at least 45–90 ft. tall and 45–75 ft. wide, sugar gum is familiar as


How to Grow Eucalyptus


PLANTING Buy vigorous- looking plants; they are not necessarily the biggest. Avoid those with many leafl ess twigs or evidence of hard pruning. If possible, do not buy rootbound plants. If such plants are all you can get, loosen the rootball and cut off any kinked roots that cannot be straightened; then spread remaining roots out as straight as possible (in a fan shape) in premoistened planting hole, with stem’s old soil line 1⁄2–1 in. below grade. Immediately fi ll in around the roots with moistened soil and irrigate heavily. If the plants are top-heavy, cut back and stake.


FEEDING & WATERING Complete fertilizer is seldom needed, although iron often is required for eucalypts whose leaves chronically turn yellow between veins (chloro- sis). In the desert, plants are especially subject to chloro- sis in dense or shallow soils. Iron chelate applied in spring and fall is helpful for young trees. Overwatering can cause chlorosis. Newly planted trees may need water every day for their fi rst week if weather is hot and dry. Soak deeply once every week or 10 days for the rest of the fi rst growing season. Once established, most eucalypts need no watering at all, except in the low desert.


PRUNING This is best done in early spring. Many euca- lypts need selective pruning to improve their shape or to remove dead or dying growth. Some benefi t from cutting back to make them bushier or stouter; wait until they have been in the ground for at least a year, then cut back to just above a side branch or bud. If there are no side branches or visible buds, cut back trunk to desired height— if the plant is established, new growth will break out beneath the cut. Later, remove all excess new branches that form; keep only those that are well placed.


PESTS The eucalyptus long- horned beetle—fi rst observed in Southern California in 1984—has now been suc- cessfully controlled by natural predators introduced from Australia. But several other beetles, at least one gall wasp species, and as many as eight psyllid species have been introduced since then. Without natural predators to keep them in check, many have become serious pests, especially on stressed trees.


Beetles. Signs of long- horned beetle infestation include oval holes in the plant’s wood, and individual branches or the whole plant dying with its leaves still attached. If you see tunnels under bark of fi rewood, imme- diately burn or bury the wood. Remove dead or dying trees; bury logs or cover tightly with tarpaulins for at least 6 months. Tightly cover eucalyptus fi rewood and do not transport it.


Psyllids. These tiny insects suck sap from leaves, excret- ing honeydew in the process; foliage may look black due to sooty mold growing on the honeydew. If present in high numbers, the pest can cause severe leaf drop. Infested plants are more susceptible to attack by other pests, including borers. Minimize stress by irrigat- ing deeply (but not near the trunk) during long dry spells; don’t fertilize. Don’t spray leaves with any kind of insec- ticide—parasitoid wasps have been released to control the psyllid. Soil drenches and trunk injections of the sys- temic insecticide imidacloprid protect healthy trees from psyllids. For the most current


information on pests of eucalyptus, including resis- tant species, contact your county’s Cooperative Exten- sion Offi ce.


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