HOW TO GROW A EUCALYPTUS


This page deals with the aspects of growing eucs assuming you have started with a potted plant.  To read about starting from seeds, please read Growing eucalypts from seed.

PLANT SELECTION: First off, you must decide right from the start whether you intend to keep the plant permanently in a pot or whether it will go in the ground.  If the euc is to stay in a pot all its life, you need not be too choosy as long as the plant looks healthy and appeals to you.  However, choosing a euc to plant out into the ground requires being much more selective and careful about what sort of tree you choose.  (To determine which species is most suitable for your outdoor site, please see Choosing a Eucalyptus for your site and climate.)

Eucs are very sensitive to root damage and restriction.  It is therefore essential to select a small tree (generally about 1 - 1.5' tall) that is not potbound, and that looks healthy and vigorous.  It is very much to the benefit of the tree for it to get established in the ground and growing in the native soil as a small plant.  There are numerous other benefits to starting with small plants.  Large, top-heavy, or rootbound potted eucs are generally problematic.  For more information about why this is so, please read Eucalyptus growth rate, and the importance of planting small.  More specific information about how to select a euc can be found under What size tree to choose and what to avoid.

PLANTING TIME:  Once you have obtained your euc, it is important to plant it out in its permanent location immediately before it has a chance to become rootbound and lose its vigor.  Generally, eucs can be planted at any time of the year.  However, if you live in a climate where your euc is expected to be marginally hardy, I would advise planting it in mid-spring so that it can reach the maximum possible size before the following winter.  Similarly, if you have hot dry summers and anticipate that it will be difficult to keep the euc watered, it may be best to plant it in the autumn (or the beginning of the rainy season).  These are very important factors to keep in mind while deciding when to purchase your euc, because it should be planted immediately after purchase!

If you have got yourself in a fix and purchased your euc at a less than ideal time of year for planting, there are several things you can do.  If you did not pay too much for it and another one can easily be obtained in the future, I would suggest planting it immediately in spite of the risk.  The risk of losing your euc to heat or cold is worth it, considering how much faster it will grow if planted immediately upon receipt.  If the risk is winter cold, potting the euc into a somewhat larger pot and placing it in a very sunny window indoors (or in a sunroom) just for the winter is an option.  But be aware that they demand a great deal more light than indoor plants and may become unstable or rootbound from remaining too long in a pot.  If the risk is heat/drought, bear in mind that about any euc (if that species is heat tolerant to begin with) will probably be all right if watered daily though hot periods.

PLANTING METHOD: Once you have chosen a healthy tree of the suitable species for your site, there is nothing too complex about planting eucs:

Dealing with rootbound trees: If you have a potbound tree to plant in the ground, it can still possibly make a good tree.  Generally the guidelines above should still be followed.  The most important thing to do is ensure that the roots are untangled very thoroughly and spread out straight from the center (as described above) when it is set in the ground.  You may have to break quite a few roots to make this happen, but try to break as few as possible.  Do not slice the rootball up with a knife or rip off large mats of roots - just untangle as much as possible, cutting only as a last resort.  Water the tree in.  Do not expect vigorous growth until the tree has been well cared for over a couple of years.

Dealing with root-damaged trees: Trees that have had a large amount of their roots cut off lose their vigor.  This includes trees that have been dug up and moved.  They can be planted as described above, but if the root loss is significant, it some of the top growth should be cut off to compensate for the root loss.  They too will not make vigorous growth very soon after planting.

Dealing with top-heavy trees: If the tree is top heavy and will not stand on its own when planted, or appears at risk for windthrow, it should be cut back hard to reduce the weight of the top growth.  You can even remove 60 - 80% of the tree's top growth and it will be fine - it will grow back very vigorously and much more sturdy.  In extreme cases, it may be a good idea to cut the tree back all the way to within a couple inches of the base - it will still regrow, and have a nice big sturdy stump to hold it in place.  Staking the tree will not correct top-heaviness; it will just worsen the problem.


Why staking is harmful

Eucs can be somewhat succeptible to blowing down in heavy winds.  Staking is useful for some kinds of trees to train them to develop a good straight leader, when they might not do so on their own.  It does not actually strengthen the trunk.

Eucs are very capable of growing a strong leader on their own, and therefore do not require staking.  The leader is not always straight, but it often is, and even slightly leaning trunks are very picturesque and not undesirable.  Staking a euc causes it to grow a weak trunk, and the tree will be succeptible to blowing over.  The trunk will be much stronger if it is allowed to sway and flex with the wind.  Even if the tree does not stand quite as straight as you would like it when larger, it is invariably better off without a stake.

CARE AFTER PLANTING: Eucs require relatively little care after planting.  Although many eucs are very drought tolerant once established, they must not be allowed to dry out when they have just been planted and are small and vulnerable.  You may need to water the euc as often as once a week to once a day, depending on the consistency of your soil.  Just do whatever it takes to keep the soil moist until the euc is well established and has grown several feet.  Of course if the soil remains moist because of frequent rains (i.e. in the eastern U.S. or Europe) or lawn irrigation, then no supplemental watering is needed at all.

I generally recommend mulching the euc, especially if it is growing in a site where the soil is liable to dry up or freeze or become infested with weeds or grass.  If you have a mild climate, mulch might not be necessary in a garden setting where weeds remain under control and the soil remains moist.

There are several benefits to mulching.  The mulch will help prevent the soil from losing moisture through evaporation.  It will help keep the soil from freezing, which can be a crucial factor in winter survival.  Weeds and grass should not be allowed to grow up around the base of the euc or they will slow its growth by competing for nutrients and moisture.  Mulch can prevent this as well.  (This problem, it should be noted, is not as serious as the problem of eucs being slowed from having their roots restricted, because it is very easy to correct.  In some situations, grass competition is not even regarded as a problem, since eucs are subjected to these conditions when growing in their native habitat.)

Mulch the euc heavily - about 3 - 6" thick is fine (so long as the weeds/grass can't grow up through it), and mulch the ground about 1.5 - 2' out (or farther) from the trunk of the plant.  With eucs it is OK to bury the base of the tree a little bit.  Many products can be suitable for use as a mulch, including bark, wood chips, leaves and grass clippings.  Compost, manure and other products containing a lot of nitrogen are generally less suitable, because weeds will grow up in them more readily, and because they will cause the tree to produce too much top growth for the size of the root system.

If browsing by animals is likely to be a problem, a wire cage of some sort can be set up around the euc to protect it.  Creatures such as deer do not generally like eucs, but may nibble a branch or two off, or scrape the bark of with their antlers.  The euc will recover from this, but of course it will be damaged some.
 

Eucs should not be transplanted.  That is, if you have planted it in one place in the ground, and it becomes established there, you should not move it.  Eucs are much more sensitive to root damage than normal trees when young.  If you dig it up and fail to get at least 40 - 80% of the roots (this can vary according to the time of year), then the tree is likely to die outright.  Even if it survives transplanting, its vigor will be greatly reduced.  "It is therefore important to ensure that they are planted where they are to grow to maturity in the first place." (- Quote from Eucalyptus Nurseries website)

LONG TERM CARE: Eucs need relatively little care in the long run.  They do drop a lot of leaves and bark, but these do not necessarily need to be cleaned up (depending on the situation) since they will provide beneficial mulch for the tree.  The only problems that may require extensive care are generally a result of choosing the wrong species for the site.  Examples of this would be having to frequently irrigate a species that is not drought tolerant, or having to cut the roots of a tree that was planted too close to a sewer line, or having to top a tree that was planted too close to the power lines.

Preventing and correcting windthrow: Windthrow is liable to occur with eucs that were planted as large or top-heavy trees, but may even occur with trees that were planted small.  It is especially prone to occur in wet, heavy soil when it is very saturated.  Several factors come into play here.

If you have an exposed, windy site; it is important to choose a species that will stand up to those conditions - see Choosing a Eucalyptus for your site and climate.  A clue can be taken from the conditions under which each species is found in its native habitat.

One preventative measure is to "grow the tree tough" - that is, withholding mulch, allowing grass to grow up around the tree, allowing the tree to go somewhat dry during the dry season, and other such practices will prevent an excessive amount of top growth from developing.  Such conditions are reminiscent of how eucs grow in Australia, but the drawback to this treatment in cultivation is that they will not grow very quickly.  Another preventative technique is to cut back the euc hard just once after a year or two of growth (or periodically) so that a very thick, sturdy trunk will build up at the base.  This should not be done in the autumn or frost may severely injur the cut.  A third possible technique would be to prune out a large fraction of the branches in the crown without reducing the tree's height.  I am not sure how well this works in the long-term, as it is liable to cause vigorous regrowth near the top which will just start the problem over again.

If the tree is windthrown, the solution is not to stake the tree - this only worsens the problem.  The trunk can only regain its strength if it is allowed to sway and move with the wind.  Windthrown trees can be restored by tying them to sturdy, stationary objects several feet away from the trunk (sometimes even quite far away), or tying them to each other, in such a way that the tree will still stand reasonably upright but can still move around some when the wind blows.

Pruning: Eucs do not generally need to be pruned.  However they are very responsive to pruning and will resprout vigorously from very large branches.  A large proportion of the foliage can be removed from the tree if necessary.

Generally speaking, there are so special techniques for pruning eucs that differ greatly from the pruning of other trees (besides the special treatments prescribed for certain problems as discussed above).  However, a few points should be noted:

If the euc freezes: Most eucs develop a swollen root called a lignotuber (see pictures below).  The lignotuber enables the tree to grow back from the base after fire (which is common in Australia), or a freeze which kills the top, or if the tree is cut down, or destroyed by severe coppicing or grazing.  Even if the entire top of the tree is lost, new growth will begin to emerge from the lignotuber some time after the damage.  It begins to develop several months into the tree's life at ground level.  It is very prominent and visible in many multi-trunked (mallee) species, and less prominent but still present in most other species.  Many species such as E. regnans, E. fraxinoides, some forms of E. nitens, E. obliqua, E. globulus, E. delegatensis, and others, do not develop lignotubers.  They will not regrow if the top freezes (and make poor coppicing subjects).

Eucs are inclined to grow more prominent lignotubers under "tougher" conditions.  If a tree is growing in good garden soil and has made a lot of very vigorous top growth, the lignotuber will not be as well developed.  This can make it difficult for the tree to recover if the top freezes.  This is part of the reason I recommend against feeding eucs a lot of nitrogen, besides that it will be succeptible to blowing over.  A strong lignotuber and root system will reduce the risk of the tree being lost both from blowdown and from freezing.

If a severe freeze strikes, the degree of damage to a euc is usually not apparent immediately.  On occasion it may even take a year or two to tell whether a certain part of the tree is dead or not.  There are many mechanisms which determine where and how extensively freeze damage takes place on the plant, and these mechanisms are not well understood.  One major problem tends to be when the bark splits at the base of the tree.  When this occurs it is a sign that the growing tissues (cambium) in the tree's trunk have been damaged by cold.  This is especially a problem for younger eucs, because they have very thin bark at the base of the tree which does not insulate the cambium.  Often the top of the tree may appear to survive the cold, only to shrivel when damage to the trunk manifests itself.  It might be possible to reduce this risk by burying the lower trunk in leaves or some other light mulch for the winter.

Obviously, if the tree freezes, the dead portion should be removed so that it may grow back.  But sometimes it may take a while to tell if the top of the tree is dead.  If the tree has a prominent lignotuber and was healthy prior to the freeze, it generally works to wait until you are certain which parts are dead before removing them.  By this time perhaps it will already be growing back.

Because trunk damage is often difficult to assess before it is too late, it may occasionally be beneficial to remove the top before it is obviously dead.  Although I do not know this as a fact, I would speculate that there are some cases in which this would save the life of the tree.  The reason is that on occasion, if a marginal species incurs some bark damage at the trunk base but the top is still healthy, the bark damage may catch up with the tree later in the spring when more water and nutrients are demanded from the root system, causing the top to shrivel.  And when regrowth from the lignotuber occurs, it may not survive, because the tree has expended all of its energy trying to restore the top growth.  So in theory if the tree could be stopped from expending its energy on the top growth in cases where the top will eventually die (by cutting the top off early), its chances of survival by regrowing from the base would be increased.  This is especially true of trees that are marginal for the freeze and that have lignotubers that are present but not prominent.  It would take very careful judgement to apply this idea.
 

Growing eucs for cut foliage (coppicing)

Because eucs have attractive juvenile foliage, there has always been an interest in growing eucs strictly to use for cut foliage in floral arrangements.  E. pulverulenta is the species most commonly used for this, but almost any species will work as long as it is fast growing and can recover from frequent hard pruning.  (Species that do not develop lignotubers as discussed above are less than ideal.)  Other popular species include E. glaucescens, E. parvula, E. crenulata, E. cinerea, E. urnigera, and E. coccifera.  In my opinion E. bridgesiana, E. perriniana and E. risdonii also have great potential.

The usual method is to allow the euc to establish and grow in the ground for 2 - 3 years, then cut it back hard to within a foot or two of ground level.  It will then produce a lot of attractive new growth at once which can be harvested and treated a few months later.  The eucs should never be pruned hard when there is the risk of frost in the near future - this is a frequent cause of failure for cut foliage operations in cold climates.  The frost causes the bark to split away from the cut before it can heal and damages the tree even further.


Eucs as potted plants

Eucs can be grown as potted plants or tub plants, although they generally do not make good long-term pot subjects.  They grow so fast that they can outgrow their pots and become leggy very quickly.  The larger the pot is, the longer the euc will last - I suggest using at least a 10 - 12 gallon pot, or better yet, a half-whiskey-barrel.  Once the euc gets too large for its pot, it ought to be discarded rather than planted in the ground, because of the problems associated with planting large or potbound eucs as mentioned elsewhere on the page (see Eucalyptus growth rate and the importance of planting small).  Therefore it is important to decide very early on whether you wish to grow your euc as a permanently potted plant or a permanent landscape subject, rather than changing your mind after it is too late.

If you intend to keep your euc permanently as a potted plant, you need not be so choosy as to what to look for when selecting one.  Even if the euc is slightly overgrown or rootbound, it does not matter so much since you do not need it to be extremely vigorous.    If you want it to last as long as possible, I would suggest using a smaller species such as E. vernicosa, E. kybeanensis or E. gregsoniana.

Eucs in pots must never be allowed to go completely dry.  Although many euc species are very drought tolerant once established in the ground, this is not the case when they are growing in pots.  The soil may be very nearly dry and the euc will be fine, but if it becomes completely dry the plant will shrivel very quickly.  Usually once they begin to wilt, the wilted foliage will not regrow - if the whole plant wilts, it may die.  This can happen very quickly so the amount of soil moisture should be monitored closely.  Do not flood the pot for very long though, because like any other potted plant it is also possible to overwater them.

Eucs demand a great deal of light when grown indoors - even as outdoor plants, very few of them will tolerate shade (see Choosing a Eucalyptus for your site and climate).  This can make them difficult to accomodate indoors, especially over the winter in cool rainy climates.  They should be placed in the brightest possible place, such as a sunny south-facing (or north-facing, in the Southern Hemisphere) window.  (A sunroom or greenhouse is even better.)  Potted eucs can also be moved indoors for the winter and moved back outside for the summer (which is convenient in climates too cold to grow them outdoors permanently).  However if they are moved from a bright shady spot into full sun, the leaves will scorch just like any other plant.

If a potted euc is left outside over the winter, it will be less hardy than the same species grown in the ground.  It will still be able to toelrate some frost, but care should be taken not to leave it out during a very severe freeze.

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