Eucalyptus niphophila, Eucalyptus Debeuzevillei, Eucalyptus Eucalyptus archeri, Eucalyptus gunni ‘Divaricata’, Eucalyptus perriniana and Eucalyptus neglecta are among the most hardy trees for a temperate climate. It’s a mystery why these species aren’t generally available in our climes. All you ever see are half-hardy forms of Eucalyptus gunni on sale. The hardiness of a species is largely dependant upon the seed origin. There are places in Australia where extreme frost occurs regularly. Seedlings from such locations are much stronger than those from trees growing in milder circumstances. Eucalyptus gunnii does not only occur in low land Tasmania; it also grows at 1200 meter (3600 feet) and tolerates considerable frost there. Seedlings from these trees have the best chance of success here. During very wet winters Eucalyptus trees are more prone to freezing (if the bark splits) than during normal winters. Fortunately, there are nurseries who pay special attention to the provenance of the seeds, and ‘de Groene Prins’ offers young trees from these sources. De hardiness of seedlings is variable, though, so not every individual of a species is as hardy as the other. In any batch there will be variation. The altitude at which a plant grows in nature is only partly determinant for it’s hardiness. Eucalyptus debeuzevillei is for example hardier than Eucalyptus niphophila, yet it grows 400m (130 feet) lower down the mountainside. To summarize: Eucalyptus debeuzevillei and Eucalyptus niphophila are the hardiest species, which often survive even the severest of winters. Other hardy species survive average winters without any problem.
Rapid growth of Eucalyptus
Growth can be at most 2,5m (7,5 feet) per year! Eucalyptus gunnii, nitens and perriniana are particularly quick growers. The tallest species here attain about 10m (30 feet). All of them can be pruned well. To get a strong tree, it is advisable to prune back even to a half the size – but only this severe with Eucalyptus archeri, Eucalyptus gunni, Eucalyptus gunni ‘Divaricata’, Eucalyptus glaucescens, and Eucalyptus perriniana. This has the advantage of making the trunk somewhat heavier in relation to the top of the tree. If you wish to harvest the green branches, then you can prune the trunk in march at about 50cm (20″) above the ground. The trunk should be at least 5cm (2″) thick, so let the small ones grow a little first. (Eucalyptus debeuzevillei, Eucalyptus nitens, Eucalyptus pauciflora and Eucalyptus niphophila are less suitable for this).
WHERE TO GROW YOUR EUCALYPTUS
Full sun is necessary. Never plant under high trees! Eucalyptus archeri, Eucalyptus debeuzevillei and Eucalyptus niphophila tolerate a windy place. The last two even tolerate sea wind. Choose a permanent place for your eucalyptus straight away, as replanting can turn out badly. Supporting your tree at about 30cm (12″) against a low tree-stake is recommended. Eucalyptus neglecta and Eucalyptus Crenulata tolerate light shadow.
TYPE OF SOIL
It’s not necessary to improve your soil, so don’t use any compost or enriched soil. Heavily fertilized trees can easily blow over. Only work some compost through really poor soil. It is important to keep the earth weed-free to 60cm (25″) from the trunk. This is especially important in the first years to ensure optimal growth. Avoid weed-killers, Eucalyptus is extremely sensitive to these. The best mulch against weeds is pine-bark shavings.
Eucalyptus for wet soil:
Absolute min temp in °F / °C
Eucalyptus aggregata -3 / -19.5
Eucalyptus camphora +3 / -16.5
Eucalyptus cinerea +8 / -13.5
Eucalyptus dalrympleana +3 / -16.5
Eucalyptus glaucescens -2 / -19
Eucalyptus gregsoniana +3 / -16.5
Eucalyptus gunnii -5 / -21
Eucalyptus rodwayi -3 / -19.5
Eucalyptus rubida +3 / -16.5
These minimum temperatures relate to occasional, short cold-snaps and wind-free conditions! Extended periods of frost can be fatal.
On chalky ground (pH > 7.5)
All the species mentioned here have white to creamy-white flowers. The ones with pretty red flowers are unfortunately not hardy here. The flowering period varies from species to species. Eucalyptus debeuzevillei and Eucalyptus niphophila usually flower from their 5th year. Eucalyptus gunni and Eucalyptus perriniana can bloom from their 4th year on. Eucalyptus archeri even flowers from its 3rd year on. Pruning inhibits flowering. Flower buds take a year to turn into flowers! Sometimes flowers, buds and seed pods can be seen on the same branch.
When the trees are still small it’s advisable to protect them in the winter with pine branches or reeds. Winter sun during frost periods can cause damage to the leaves. Also, the bark can split, which can lead to the plant dying. Sometimes the plants freeze off and new shoots will appear from the thickened base of the tree, called lignotuber. Don’t forget that Eucalyptus, whilst not fully winter-hardy, show great adaptability! Selecting the hardiest seedlings and propagating further from these is a process which has only just begun. With luck you can have a magnificent garden tree within years. The trees in our jungle garden are living proof of this! In the following table you can see where each species comes from and how quickly it grows. Hardiness is indicted by the following words: Very good : application everywhere in NL and B is possible, even in unprotected areas. Good: the location should be moderately protected, severe winters could be fatal Reasonable: the location should be well protected by walls, thick conifers etc. Limited: situated only to coastal areas Weak: only survives mild winters.
The following list is limited; there are more species but these have not yet been sufficiently tested. In a protected town garden you can do much better than here in the open countryside!
INFO PER SPECIES
|Species||Speed of growth||Hardiness||Origin|
|coccifera||moderate||limited||Tasmania 1100 m|
|debeuzevillei||moderate||very good||ACT. 1900 m|
|glaucescens||fast||good||N.S.W, 1700 m|
|gregsoniana||moderate||redelijk||N.S.W. 1300 m|
|gunnii||fast||limited||Tasmania 1200 m|
|gunnii ‘Divaricata’||fast||good||Tasmania 1150 m|
|mitchelliana||moderate||limited||Victoria 1700 m|
|neglecta||fast||good||N.S.W. 750 m|
|niphophila||moderate||very good||N.S.W. 2300 m|
|nitens||fast||minimal||N.S.W. 1400 m|
|parvifolia||moderate||good||N.S.W. 1100 m|
|perriniana||fast||good||N.S.W. 1600 m|
|rubida||fast||limited||N.S.W. 1200 m|
|vernicosa||slow||redelijk||Tasmania 1000 m|
Eucalyptus repels insects!
Insects avoid Eucalyptus; because of this they are being planted en masse as an experiment to frighten away tics. We are also removing indigenous trees, as tics prefer oak, beech, etcetera.
(however as long as wildlife wanders around, tick invasion continues)
Eucalyptus and global warming
As extreme winters are possibly consigned to the past, Eucalyptus can have a great future in our climate! Nowadays many more species are being tested than in the past. I test five plants of each species together, the idea being to progressively select the best and increase the chance of improving the plant. Maybe by selection and crossing on a larger scale we will work towards plants which develop well in our climate. 45 years of field trials in Southern France has encouraged us to continue. Many species grow almost year round and are hungry CO² eaters.