Growing Eucalyptus From Seed

Table of Contents and IntroductionAfrican Violets: the Doyen of House PlantsAgapanthusAlstroemeriasAmerican SagebrushesAmerican WildflowersAndean Nymph - a pink mimulusAquilegias (Columbines)AuriculasAustralian AnnualsBellis Perennis (Daisies)Black-Eyed SusanBlue African LiliesBreeding DelphiniumsBreeding Fuchsias: Part 1: From SeedBreeding Fuchsias: Part 2: HybridisationBromeliads from SeedButterflies in Soy SauceCacti RaisingCampanulasChilean Bell FlowerChilly Treatment for Peruvian LiliesCollecting SeedConserving Annuals and BiennialsCosmosCucumbersCycads: Living FossilsCyclamen for IndoorsDahlias from SeedDamping OffErythroniumsF1 Hybrid - What Is it?F2 and Open Pollinated VarietiesFrom Obscurity to the Height of FashionGentiansGeraniumsGermination to Pricking OutGolden Impatiens - The StoryGrowing Alpines From Seed: Part 1Growing Alpines From Seed: Part 2Growing Bananas From SeedGrowing Cyclamen From SeedGrowing Eucalyptus From SeedGrowing Ferns from SporesGrowing Foxgloves From SeedGrowing Fritillarias From SeedGrowing From Seed: From Packet to SoilGrowing Hardy Ferns from SporesGrowing Hardy Geraniums From SeedGrowing Lewisias From SeedGrowing Magnolias From SeedGrowing Meconopsis From SeedGrowing Proteas and Related Genera from SeedHandling Small SeedsHardy Annuals: Part 1Hardy Annuals: Part 2Hardy CyclamenHardy SpurgesHelleboresIncreasing your Violas and ViolettasKeeping Records of Seed SowingLettuce - the Vital Part of any SaladLord Anson's PeaMagnolias - the Root of the ProblemMimulus from Seed to Seed in Sixty DaysNew Guinea ImpatiensOld-fashioned Sweet PeasOnions with EverythingPansies are not Difficult to Grow from SeedParsleyPerennials for American GardensPetuniasPhygelius - their cultivation and propagationPinks: Evocation of the PastPlants That Flower OncePrickly but NicePropagatorsRadishesRaising PalmsRaising PrimulasSalad Leaves - a lot to be desiredShow Stoppers Twice OverSowing SeedsSowing in Open GroundSowing to Feed our FriendsSturt's Desert PeaSweet Peas - Autumn SownSweet Peas - Sowing and GerminatingTall and HandsomeTechniques with Tiny SeedTexas BluebellThe Effect of Light on Germination and SeedlingsThe Nervous PeaThe Scarlet Welsh PoppyThe Search for the Yellow Sweet PeaToad LiliesTomatoesTreasure Hunt for TasteUnderstanding Latin NamesUnique Poppy (Mother of Pearl)Viability of VegetablesWeaning SeedlingsWill the Real Mimosa Please Stand Up

Unique amongst trees, eucalyptus are fast growing and elegant but also have some more unusual characteristics. John Kelly describes their features and dispels a few myths about how to raise them.

Eucalyptus is a strange genus, consisting of trees that are quite unlike anything else. Their flowers, whose beauty is owed entirely to the stamens, are fairly typical of other genera in the family Myrtaceae, such as Callistemon and Melaleuca, but beyond that they stand alone. Evolution has taken them along a path that has been followed by no other trees or shrubs so that, although you can spot a eucalyptus at a glance, you may find it very hard, even if you are pretty knowledgeable, to tell what species it belongs to.

All except two or three species have rounded juvenile leaves and more or less sickle-shaped adult ones. Moreover, the juvenile leaves are opposite, while the adult foliage is alternate. The adult leaves do not spread their surfaces to the sun, as do those of almost all other broad-leafed trees, but hang in a way that actually minimises the incidence of sunlight on their surfaces. As an adaptation to a hot, dry climate, this cannot be bettered; it also allows every drop of available rain to reach the root area and it means that eucalyptus do not cast heavy shade in our gardens.

All eucalypts contain a gum which is highly volatile and which becomes a gas in fire conditions, so that a forest fire can jump what could be substantial fire breaks in any other kind of forest. The gums and oils do, however, lend a delicious range of aromas to the foliage. On the other hand, like resinous trees, eucalypts are just about impossible to propagate from cuttings and must be raised from seed.

Another peculiarity is that most of the species grow in a very wide range of conditions, especially altitudes. This is a major reason for many of the misunderstandings and dogmatic statements that occur concerning their hardiness.

Hardiness

The provenance of a eucalypt - what part of its range the seed came from - is all-important. Where a species occupies a range in which altitude changes markedly, those specimens at the higher levels will be hardier than those lower down, and their seed will produce plants that are hardier as well.

One of the myths that gardeners put about is that eucalyptus become acclimatised to their conditions in cultivation and that successive generations grown from garden-saved seed will produce hardier and hardier trees. This is arrant nonsense and implies the inheritance of acquired characteristics, a notion that went out with Darwin. What happens is that trees from hardy provenances are the ones that survive to produce seed in cultivation, while those that are not die out.

Imported wild seed should, then, be from as hardy a provenance as possible unless one is doing one's gardening in Southern California, Florida, or at one's holiday villa in the Canaries. Even so, the tropical eucalyptus, such as E. ficifolia, will succumb in such freezes as occurred in Northern and Central Florida in 1983 and 1985. The importance of provenance can be well illustrated by a tree of E. nicholii which reached 60ft (18m) in Dorset, England and survived many severe frosts. Only temperatures of 10F (-12C) caused it to lose its branches, after which it regenerated from the trunk. All the available literature says that it is not hardy in the British Isles, but that is based on trees from the lower part of its altitudinal range.

The increasing availability of seed from hardy provenances has greatly increased the number of species that can be grown in frosty climates. Whereas some years ago there were about three, this has now increased to well over a dozen with about thirty in all that are able to withstand the milder kinds of cool-temperate climates.

This means that the sub-tropical effect that is given by eucalyptus, especially by means of their often strikingly blue-grey foliage, can be obtained in gardens that are far from sub-tropical. Their use is not confined to large gardens either as there are several that are quite small. Not only that, but there is another peculiarity of the genus that allows a great many of its members to be used in gardens in a way that is unique among trees.

Use in the garden

Eucalyptus are lavishly furnished with latent buds and there is a high concentration of these just above ground level. In some of the smaller ones there is a woody swelling at the base of the trunk called a lignotuber. This contains a great many buds and it is this that produces a dense thicket of quite short stems if the tree is damaged or, in many cases, even if it is not. These eucalyptus are called 'mallees'.

Others, if cut to ground-level by frosts, will react as mallees do and produce a great many new stems. It is possible either to allow the newly bushy plant to grow as it will, or to select one strong stem and to encourage it to grow up as a new trunk. Similarly, a eucalypt in a small garden can be cut down by the gardener and grown either as a multi-stemmed shrub or be given a fresh start as a tree.

The seed-pods are important in the identification of Ecalyptus. They are very varied in their sizes and shapes and may be, for example, urn-shaped, top-shaped, hemispherical, or rather like small pears. They are furnished with valves which open to release the seeds, but the capsules are hard and woody and it is not easy to tell when the seeds are ready for collection; all that happens is that the valves, which are rather small, open. There is no splitting of the capsules such as occurs with so many plants and which is relatively easy to observe.

Seed will usually take at least a year to ripen and it is not easy to know when this will happen for a given species in cultivation. Indeed, some species will obstinately refuse to release their seeds for several years although oven-heat will often do the job for them.

Those who have established specimens of Eucalyptus species will soon learn when to be on the look-out for ripened seed. It is certainly a good thing if seed from trees that are known to survive hard conditions can be saved, so home-harvesting is to be encouraged. Where this is not possible, though, the best and most reputable seed lists should be sought out as it is likely that responsible seedsmen will have recognised the necessity for securing seed from hardy provenances.

Seed sowing

To those of us who apply some thought and a lot of empiricism to gardening, it is a constant source of amazement to find that it is the subject of so much bunkum and claptrap. We have already seen one example of kindergarten logic being applied to Eucalyptus; another has to do with sowing their seeds.

It is perfectly true that species which have adapted to surviving forest fires will store their seeds against such an eventuality so that, after the passing of the fire, there is an abundant germination in order that the population should regenerate. However, it is complete poppycock to aver that fire is necessary for their germination. It is, in fact, to fall into that most elementary of logical traps, post hoc ergo propter hoc - the belief that if one event follows another, the first one caused the second.

Why then, has the legend been perpetuated that it is necessary to subject eucalyptus seeds to fire in order that they will germinate? Possibly because plant material that comes into our hands is precious and we are reluctant to experiment. If someone who appears to be knowledgeable, or who has a reputation as a writer or broadcaster of some standing, tells you that a certain method is essential, then it takes courage to ignore him and try something else. The chances of wasting the material appear to be high.

The great majority of eucalyptus seeds will germinate perfectly well and very quickly if they are merely gently pressed into the firmed surface of a compost, preferably a soil-less one, and not covered with soil at all. The often larger seeds of the tropical species, such as E. ficifolia, will benefit from a light covering of sharp sand but that is all. Bottom heat is very desirable indeed and will promote a high rate of germination, but its absence does not mean that total failure will ensue - cold conditions will enable a reasonable proportion of seedlings to result.

Many of the ovules in a seed capsule will not have been fertilised and these emerge as red, or reddish-orange granules among which are the fertile black seeds. Failure has often been ascribed to other factors when, in fact, there has been little or no true seed present in a batch. There is no point in wasting time trying to separate the seed from the red bits; sow the lot, it does no harm.

Apart from these provisos, eucalyptus seed requires the same conditions for germination as most other trees and shrubs and is best sown in the very early spring. In the northern hemisphere, February is the best month, and about the middle of the month at that.

Planting

One of the reasons for recommending sowing as early as possible is that the planting of Eucalyptus species should be done in the mid-summer of the same year, so they need as much time as possible to attain some size. Most will be about 8-9 inches (20-23cm) high by this time.

If this sounds odd, there is a good reason. It is odd. Eucalyptus are extremely difficult to make wind-firm, and they will never become so if they are the slightest bit root-bound. They should never be staked. The Australians, who should know, say the bigger the stake, the taller the eucalypt will be when it falls down. It is possible to plant much larger plants, but they will eventually have to be cut down to ground level and started again - a great waste of time. Nurserymen advocate this method because they want to sell plants that will command much higher prices than four-month-old seedlings.

Such a little plant will, on the other hand, grow rapidly until the autumn and will continue to grow during mild spells in the winter. Given a little protection during cold periods it will really take hold the next year and will grow into a pencil-straight tree which will stand up to the strongest winds.

Finally, just to be different again, eucalyptus should never be planted with any manure. Once they have grown to some size and strength a top-dressing around the root area is a good thing, but manure at planting time will have one certain effect. They will fall over.

Hardy species

The following species have proved to be hardy in climates where temperatures as low as 5F (-15C) have occurred for periods of some days:- archeri, cocci/era, fraxinoides, gunnii, johnstonii, niphophila, nitens, pauciflora, perriniana, stellulata, viminalis.

Plants from tender provenances may succumb to higher temperatures.