Cordyline australis is also commonly called the cabbage palm or giant dracaena. It is a warm-season plant that can be grown indoors but, because it eventually reaches 15 feet tall, it is also an outdoor plant. The tree starts out with a subterranean trunk that will eventually emerge and propel the plant skyward. It is tolerant of a wide range of soil types and thrives in either full sun or partial shade. The plant has few pest or disease issues but is considered invasive in tropical climates.
Cordyline is not considered a pest plant, but it has escaped cultivation in California and become naturalised. The problem with this is the displacement of native species. The plant bears a small cluster of white flowers which become a berrylike fruit. The birds enjoy these fruits and then excrete the seeds into native ranges. In states with climates similar to the native habitat of Cordyline, the plant will germinate readily.
Cordyline requires moderate watering during the growing season. This is from early spring until fall. If the plant is grown indoors, care must be taken not to over water it. When the heat is on in winter the plant needs supplemental humidity because the furnace tends to dry out the air. Both over watering and under watering can damage the plant. Excess water can cause rot and too little can cause outbreaks of spider mites and other problems. The cabbage palm is best grown in well-drained soils. For the exterior plant a soil mix with plenty of sand or grit will ensure adequate drainage. The potted interior plant should be in an unglazed pot with open drainage holes.
Cabbage palm is not really a palm but it is a tropical to semi-tropical plant that has no freeze tolerance. Cordyline is hardy in U.S. Department of Agriculture zones 9 to 11. This means it is only going to grow in southern California, Florida, parts of Texas and a few other very warm regions. The plants are native to New Zealand and thrive in hot temperatures. Temperatures that near freezing cause the tree to go dormant and freezing temperatures will kill the top and usually the root of the tree.
Cordyline plants that are containerised indoors experience the most problems with pests. Scale insects, which are armoured sucking insects, may be found on the leaves and stem but seldom cause any real injury to the plant. Mealy bugs live in the soil and are common in houseplants. They can be difficult to remove but consistent applications of an insecticidal soap or Bacillus thuringiensis can be helpful. Spider mites are also sucking insects and are identified by the presence of webbing on the tips of the leaves. They can be controlled in the same manner as the mealy bugs.