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Eucalyptus - Growing Guide
Gum tree, Ironbark
There are literally hundreds of different species of eucalyptus in Australia but relatively few of them are fully hardy in our UK climate. Ventnor Botanic Garden in the Isle of Wight has a large collection of at least 60 different species but one should not think that many of them would survive outside this strange coastal microclimate.
Eucalyptus trees grow exponentially quickly; arguably quicker even than leylandii (x Cupressocyparis leyandii), the quickest growing conifer. In a hot, dry, sunny situation their growth rates are quite remarkable and they are very resilient against wind. A huge plant of E. pauciflora by the mist houses at Burncoose stood through the 1990 hurricane when everything else around it was uprooted.
While I am only talking here about the hardier varieties which we grow that are frost tolerant in southerly UK gardens all eucalyptus are grown for their aromatic foliage and attractive bark formations. Older and more established plants will eventually begin to flower and these too can be quite dramatic in some hardier species. These are petalless but are in large clusters or umbels of stamens which appear like ‘bottle brushes’ in shades of white, creamy-yellow or red-pink.
If you wish to keep your eucalyptus under control and stop it becoming a huge tree you need to top the main stem or trunk back to around 5-6ft. The plant will then produce a mass of side shoots which are ideal for cutting and flower arranging. In Cornwall eucalyptus are grown in this way on a field scale on a few farms for the foliage market. You may well miss out on the bark and flowers but you will have a repeatable and ongoing source of cut foliage stems.
Eucalyptus are most easily grown from seed which will germinate quickly when sown in late spring or summer when the weather warms up. In Australia eucalyptus regenerate quickly from seed after bushfires.
If you live in colder areas you may have to grow (and keep cut back) more tender species of eucalyptus under glass perhaps standing them outside in large pots in the summer.
You should remember that juvenile foliage on some species of eucalyptus is very different from the leaf form of mature plants. This can, and does, cause confusion when naming them properly.
E. gunnii, the Cider gum, is perhaps the best known eucalyptus in the UK and the most widely grown. It can readily grow to 60-80ft in the right environment. Juvenile leaves are ovate to rounded but adult leaves are elliptic or ovate to lance shaped. The flowers are creamy-white in late summer.
E. nicholii has grown into a 50-60ft tree at Caerhays. It is a spreading and dense tree with a rounded crown when in full maturity. Juvenile leaves are grey to blue-green and bluish-green to green in adulthood. The flowers are white in the autumn but the Caerhays plant took 30 years to flower properly, and then, only after a hot summer. The leaves have a strong peppermint smell when crushed.
E. pauciflora subsp. niphophila, the Snow gum has a (relatively speaking) slow growth rate. The trunks display wonderful patchworks of green, grey and cream when mature. It is very hardy and the twigs have a waxy-white bloom. The leaves are narrowly lance shaped and the flower umbels are white. The tree grows with us to about 20ft.
E. perriniana, the Spinning gum, has rounded bluish-green juvenile leaves joined at the bases around the stem. Adult leaves are totally different with a glaucous pendant lance shape. This species is not so sturdy against wind and grows, with us, to around 20ft.
At Caerhays we have trialled other species. E. globulus, the Tasman blue gum, is one we have not dared put out in the garden yet and it resides by the greenhouse in a large container. This species is often used as a feature in municipal bedding schemes so definitely is not hardy. However at Ventnor it is spectacular.
Species which have been hit by the cold include E. crenulata and E. leucoxlyn ‘Rosea’. Species which so far have not been hurt by cold winters and are now established trees with great bark colourations include E. simonosii and E. mannifera var. praecox.