Eucalyptus, commonly known "Down Under" as "Gum" trees represent an enormous genus of trees and shrubs. Over 600 species have already been classified, many of these species have numerous cultivars and hybrids. At least as many more species are yet to be classified. Eucalyptus seed is unstable genetically so new species and varieties are constantly being introduced. This genetic instability is one of the reasons for the success of the eucalyptus.
The seed from a single pod often germinates into a wide variety of seedlings that vary in leaf colour and form, ultimate size and shape and even to the growing conditions they prefer! Botanists speculate that this is the reason the gum tree has so successfully colonized most of Australia even though climate and soils vary quite widely. With such a wide variety of seedlings being produced from each gum tree, there are bound to be a few that are perfectly suited to their environment.
And if that environment changes, the parent tree carries the genetic ability to produce more seedlings that are now perfectly suited to the changed situation. Eucalyptus will grow in almost any soil but prefer lighter, loose soils that drain freely. They thrive in sands, gravel, clays mixed with stone, and most poorer soil types.
While they rocket away in rich, moist soils the trees will often become quite "lazy" producing nothing more than a shallow network of surface roots that little more than balance the tree. The first strong winds usually blow these trees over. Yet, if properly planted, sheltered, and maintained eucalyptus can withstand thrashing winds, some ultimately towering to over 300 ft. and surviving for hundreds of years.
Much of the secret to growing a good gum tree lies in it's planting. Choose young, fresh trees, not overly large and in full growth, avoiding larger specimens or any that appear at all root bound. It is essential to give the tree a good, quick start with sustained growth, especially of the root system. Any check of growth in the early years is liable to stunt the root system causing disease, die-back, dropping branches, or uprooting during storms in later years.
It is ironic that most of the bad reputation gum trees have received is much more the fault of bad planting by the gardener rather than a fault of the tree itself! Late winter or spring planting is traditional but gum trees can be planted all year under suitable climatic conditions. Prune back the central leader, tips of side shoots, and remove weak or distorted growth during autumn and winter to keep the trees dense, bushy and in proportion to their root system.
E. ficifolia (Red Flowering Gum) and E. calophylla rosea (Marri) are superior flowering forms for the small garden. E. citriodora (Lemon scented or Citronella Gum), E. linearis (White Peppermint) and E. nichollii (Willow Peppermint) have great perfumed foliage. E. puverulenta (Powder Gum) gives the "blue spiral" foliage of floristry better than it's larger untidy brother, E. cinerea, the infamous Silver Dollar Gum.
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