Eucalypts as bonsai: a summary of AusBonsai posts

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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by gtrombino »

An awesome collection of accumulated wisdom, well done Phil. My newbie bonsai head was spinning with all the threads of advice; now I feel far more confident to make one of my first projects a Euc. :worship:
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

On June 27th, 2020, at 8:19 am, Shibui posted a reply to the subject "Just a couple of Eucalypts" (https://www.ausbonsai.com.au/forum/view ... on#p279766). His post included some links to great information on striking Eucalypts from cuttings. It deserves to be added to this summary of Eucalypts as bonsai. For ease of reference, this is what Shibui said:

"I have been away from cutting edge (pun intended) native propagation for a few years but remember there was some work on growing eucs as cuttings to select salt tolerant forms of E. camaldulensis. I believe they were having some success using juvenile shoots from the lignotuber after pruning the stock trees hard.

Just wondering if there have been advancements I searched and found a few interesting articles.

This one from ANPSA sets out some history and paramaters that could be useful spot to start: http://anpsa.org.au/APOL2007/sep07-s1.html
Another forestry site suggests that rooting ability is genetic and will vary from one individual to the next so forestry growers have selected high growth and high rooting clones for propagation by cuttings.

This abstract from a CSIRO research: https://www.publish.csiro.au/BT/BT9700175
The available physiological evidence suggests that ontogenetic ageing of E. Grandis seedlings involves a direct and quantitative association between decreased rooting ability of stem cuttings and increased levels of a rooting inhibitor in the tissue forming the base of the cutting. As detected by bioassay, this inhibitor is present only in adult tissue, which very rarely forms roots from stem cuttings. It is absent in easily rooted seedling stems of all Eucalyptus species tested, but it is also absent in the easily rooted adult tissue of the exceptional species E. deglupta. The ability of seedling cuttings of E. deglupta to root very easily in water provides an appropriate bioassay for monitoring the presence of inhibitor in other Eucalyptus species.
All that means it is definitely possible to strike euc cuttings but usually only from younger stems and under controlled conditions."


Thanks, Shibui. Excellent information.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

There is some debate on AusBonsai about the worth of eucalypts as bonsai material. While it is not possible to have the last word on a subject like this, it is worth noting that on 1 June 2020, Bonsai Clubs International announced that the winner of its 2020 Tree of the Year Contest is Peter Hanrahan’s Eucalyptus nicholii. Here is a link to the BCI announcement (https://www.bonsai-bci.com/index.php/20 ... ar-contest) which says:

Style: Natural Eucalyptus
Height: 900cm
Container: By Australian potter Pat Kennedy
About the tree:: Found at south Canberra Dump in the Revolve section in the summer of 1995. It was in very little soil and full of disease. (Mealy bug and sooty mildew). Over the following months I removed the pests, re-potted, cut back and trained a new leader. It was kept as an experiment, I was unsure how a Eucalypt would react to Bonsai techniques. In 1999 I potted it into a Bonsai pot and continued shaping into a gum tree style as I see in my local area. After 2001 I carved the lower and mid sections of the tree. Over the years I have had a battle with die back and have lost some of the original branches. Generally when this happens the tree goes through a redesign utilising old branches and new shoots.


Peter's achievement is worth celebrating in this conversation about eucalypts as bonsai.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by MJL »

Gee there are some fine trees at that link. Thanks for posting! A wonderful acknowledgement of PeterH’s tree and his skills and patience to get it to that level.


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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

I mentioned in my original post above that I was planning on massaging the information in AusBonsai posts on eucalypts into an article for the Canberra Bonsai Society newsletter. The first part of that article was published in the September 2020 edition of the CBS newsletter and the second part will be included in the October edition. We have a lot of very knowledgeable people in CBS and our internal consultation/vetting processes teased out a few interesting points that are worth sharing with the AusBonsai audience.

In all cases, the points raised show to the need to be careful about applying generalised information to every species – and that we have many knowledge gaps to fill in relation to eucalypts as bonsai.

Leaf reduction
One very experienced member commented on the ideas for reducing leaf size: “From my experience, it won’t work with ‘all’ species, and in some cases, it will work with some individuals of a species but not others.”

Repotting in Autumn/winter
There is a strong view that re-potting in winter is not recommended in colder climates such as Canberra. However, one CBS member pointed out that “some observations of root growth in Canberra eucs, growing in bonsai pots, showed that root growth varied between individuals of the same species. Some grew strongly in winter, while in the next pot, the same species did not grow roots in winter. Another area where we need more observations.”

Trunk/tree size
In relation to the general thinking about trunk and tree size, I received this comment from a very knowledgeable CBS member: “Here is a place where attention to the species being grown is important. Eucs that naturally grow as large trees, and shoot from the trunk, are likely to respond well to growing the trunk and chopping back hard. There are species that naturally grow to only small tree, or shrub sizes. Some of these shoot back on old wood. You can develop attractive ‘small’ bonsai with these, without going through the grow-big-chop-hard phase. Example species are E kruseana or E caesia ssp caesia. These grow well in Canberra, though they are native to SW Western Australia.”

Lignotuber/mallees
And in relation to mallees, I received this comment from the same highly qualified person: “My experience with mallees falls into two categories. First are the ones that produce the mallee form which needs complete replacement periodically. This is achieved by cutting all the existing trunks and letting a new crop grow from the lignotuber. The second are those that produce a lignotuber which produces a large number of ‘trunks’ but which progressively thins these naturally until there is only one trunk left!”

It just goes to show, we are a long way from knowing all about eucalypts as bonsai. Please keep sharing your knowledge.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

I am keeping an eye out for new posts on Eucalypts for information that warrants being included in the summary of AusBonsai posts on Eucalypts. A post on 31 December 2020, Eucalyptus melliodora, caught my eye. Here is a link to the discussion thread viewtopic.php?f=78&t=29343. It begins with this question from EdwardH:

I repotted my E. melliodora today and really struggled with the roots. I had to take a recipro saw to it and to my surprise I found a root mass which was 20cm across and 3cm deep of solid wood. Presumably many roots fused together to form a plate. Has anyone seen this happen before?

Shibui replied:

That's almost certainly the lignotuber. Many Euc species develop a swollen woody area at ground level. I believe it is a storage organ that can help the trees survive fire, drought, etc. The lignotuber can produce lots of new buds if the trunk is damaged and can also produce roots when required.

EdwardH responded:

I always thought that the lignotuber was a prominate bulge above ground like on a E. nicholli.

To which Shibui replied:

It all depends how the seedling was planted. The lignotuber develops where the cotyledons (seed leaves) were on the seedlings. Usually that's right about ground level and as the tree thickens the lignotuber grows above and below ground. Seedlings that are pricked out into tubes are often planted a little higher (or the mix compacts a bit) leaving the lignotuber exposed above ground level. As the trunk expands so does the lignotuber and eventually part of it will usually end up below the surface. I try to pot up euc seedlings just a little deeper so the lignotuber develops just under the surface. It will then develop lateral roots like yours has done and will also give a buttress to the trunk and can be exposed later.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

Two recent posts have information in them that deserves to be added to the summary of AusBonsai posts on eucalypts. Both relate to die-back:

• Mid-summer repotting of some natives viewtopic.php?f=6&t=29436&sid=f6fa021c2 ... 86#p286486
• Eucs – a cautionary tale viewtopic.php?f=78&t=29466

In the first one, Grant Bowie reports repotting a range of natives in very hot January weather. The Eucalyptus he re-potted ‘had a small root trim and tease out of roots into a larger pot’. Grant’s post triggered a strong response from other experienced growers agreeing that eucalypts are best re-potted in the hotter months. One post, however reported that a E. nicholii re-potted in December quickly died. Although no one knows why eucalypts die-back from time to time, Grant made this comment on the dead E. nicholii: ‘I note that the eucalyptus mentioned was cut back hard at end of winter. I NEVER do this. I wait till it is warm to hot before cutting or trimming foliage on Eucs. maybe that is what set it back and then the repot finished it off. Two insults too close together’.

The second post, by Gavin G, is all about die-back in eucalypts. Gavin’s post begins: ‘I have a maturing E. bridgesiana that has horrified me in the last couple of weeks. I left too much "fluff" (Gavin’s reference to fine branches and leaves) down at the base of the tree, and the whole top of the tree has died off’. He also makes the observation that: ‘Some Eucs are strongly top-dominant (like E. nicholii) but others like E. bridgesiana show a distinct preference for the low stuff - and it's way too late when you start to see the signs of failure!’ Others reported a range of die-back issues, clearly indicating that we have a hole in our knowledge – not just in terms of why this happens, and why different species have different die-back tendencies, but also in terms of the best bonsai practices to manage the die-back. And, by managing die-back I mean both understanding how best to avoid a fatal die-back and how best to incorporate die-back into bonsai design.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

Juvenile and adult leaves on eucalypts
On 11 April 2021, Shibui put a post on AusBonsai about the fact that some eucalypts have juvenile foliage that is different to adult foliage. (viewtopic.php?f=78&t=29546)
His post included this comment: “Regular pruning, as we do in bonsai, can extend the time juvenile foliage will be present.”

Shibui’s post prompted me to look into this matter a little deeper.

I found a really interesting little article on the Remember the Wild website titled “Growing pains: eucalypt leaves and tree adolescence” by Carolyn Vlasveld (https://www.rememberthewild.org.au/grow ... olescence/)

The following is an extract from the article, edited so it reads properly without the photographs. Carolyn’s article is worth a read if you are into eucalypts.

The eucalypts are a strange group of species when compared with other trees around the world. This can be partially attributed to one feature of their leaf biology. You have probably noticed it before, especially if you grew up in Australia.

The article shows two images from the same tree, a type of silver stringybark native to south-eastern Australia. Fully-grown trees of this species produce the long, hanging leaves that we would typically imagine when thinking of eucalypts. But when new trees grow, or when new shoots sprout from the base of an old tree, they grow as round leaves. This results in a species that grows different types of leaves depending on whether those leaves are on young or old shoots.

Another image shows a tree growing new shoots from the trunk base (possibly triggered by some damage at the top of the tree). When this shoot first began to grow, it produced small, round leaves, which you can see at the start of the shoot. Then, when it grew to a certain length, like a teenager experiencing a bunch of morphological changes, the shoot began to transition to the long leaves until any new leaves were completely adult in form. The round leaves at the base eventually die and fall off the shoot like all leaves do, which is why you’ll not see them on many fully-grown eucalypt trees.
The phenomenon that involves this transition from one leaf type to another is called heteroblasty. Four species around the world that exhibit heteroblasty: Eucalyptus globulus (Australia); Guzmania lingulate (the Americas); Pseudopanax crassifolius (New Zealand); Tarenna borbonica (Mascarene Islands).

Only a handful of other plants across the world also undergo this leaf change as they grow. They do it in different ways and for different reasons. Despite the rarity of this phenomenon, it occurs in hundreds of eucalypt species. This is another characteristic that makes our eucalypts so unique. But why is it so common in eucalypts compared with the rest of the plant kingdom? This is a question Carolyn is trying to answer in her research.
But it can get even more complicated than that. Different eucalypt species also do it differently. Usually round leaves transition to long leaves, but often there is also a combination of other changes, such as changes in leaf thickness, leaf waxiness, leaf vein patterns, and arrangement of leaves around the stem. In some species, trees never produce round leaves at all. For example, the Manna Gum (Eucalyptus viminalis) from south-eastern Australia always produces long leaves, even as a seedling.

In other species, trees never produce long leaves, even as fully-grown trees. They always produce the small round leaves, making them neotenous, like the axolotls of the eucalypt group, because they never transition beyond the juvenile form.
To add further complication, in some species young trees produce thin, linear leaves, and older trees produce leaves that are slightly wider (as seen in Eucalyptus rosacea of Western Australia).

These different ways of producing different leaves at different times are likely to reflect different adaptations by different eucalypt species to their respective environments. Why does a tree of one eucalypt species produce long leaves its entire life, while that of another species undergoes changes from round leaves to long leaves?

This is another question for which we don’t have an answer. So the next time you’re having a wander in the bush and spot a eucalypt, try to find some differences between the young and old growth. What kind of environment is the tree growing in? Why does it need different leaves? Or, perhaps, why does it not?
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

The Olympic Games is a bit of a distraction at the moment, but in between looking at bits and pieces I asked Google to find me something interesting about eucalypts as bonsai. One item Google offered me was nice little article titled “2016 January Meeting - Eucalyptus Demonstration” on the Bonsai Society of Victoria website. Here is a link to the article: https://www.bonsaisocietyvictoria.com.a ... onstration.

The point that jumped out for me was the paragraph saying you can promote back budding on a eucalypt by burning their leaves. I have read this advice previously, but it appears to be missing from the summary of AusBonsai posts.

This is the relevant paragraph: “Eucalypts naturally live in environments subject to bushfires and have found ways to survive. Bonsai artists can use this capability to assist in the development process. Kevin has found that burning the leaves is often a good option when a tree is doing nothing. A light scorch with burning newspaper can generate vigorous new growth opening up new development options. This can be an option in the November to March period but please don't do it on a Total Fire Ban day.”
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Matt S »

Phil Rabl wrote: July 26th, 2021, 12:41 pm The point that jumped out for me was the paragraph saying you can promote back budding on a eucalypt by burning their leaves. I have read this advice previously, but it appears to be missing from the summary of AusBonsai posts.

This is the relevant paragraph: “Eucalypts naturally live in environments subject to bushfires and have found ways to survive. Bonsai artists can use this capability to assist in the development process. Kevin has found that burning the leaves is often a good option when a tree is doing nothing. A light scorch with burning newspaper can generate vigorous new growth opening up new development options. This can be an option in the November to March period but please don't do it on a Total Fire Ban day.”
I've done this myself on Redgums that for whatever reason hadn't put on any growth for over six months. I can't confirm it works for other species but for my Redgums it resulted in new buds bursting all over the tree. As in the above example, I lit a rolled up piece of newspaper and quickly scorched the leaves all over the tree. A few weeks later the leaves had dropped and new buds were all over the trunk and branches. I'd heard of this technique from some members of the SA Bonsai Society who swore by it, and I've done it 3 times on different trees.

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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by MJL »

This is all very interesting. Thank you Phil and Matt. I have group of river gums that are in the Natural Comp and I plan to let them grow until about 1 month before the final photo date then prune to have reduced leaf size for the final photo. I don’t think I’ll burn - as I don’t want buds everywhere but… after the Comp they may get a scorch!


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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Phil Rabl »

So, why does burning the leaves on a eucalypt cause it to back bud? I’m not a scientist, but I have done enough reading to offer a summary of what scientists say. (And the substance of what I offer below has been checked over by Roger, the resident CBS botanist.)

There are heaps of articles on the Internet on how eucalypts respond to fire. Here is a link to an article by ANU scientists titled “Fire adaptive traits of Eucalypts:: https://biology.anu.edu.au/news-events/ ... -eucalpyts

It includes this paragraph: “Many eucalypts have special fire-adaptive traits, including re-sprouting after fires. This is often referred to as epicormic sprouting and is very common in eucalypts. After fires, a series of events trigger the sprouting to occur. One way this can happen is if there is damage to the top, or crown of the tree. Hormones suppressing the sprouts may stop being generated by the crown of the tree, causing the sprouting to occur. The buds of these sprouts are often protected by thick bark, which explains how they might manage to survive the intense heat of a bushfire.”

There are also heaps of articles on the roles of two families of plant hormones – auxins and cytokinins – in plant growth. Although the precise roles of auxins and cytokinins, and the complex way in which they interact, is not fully understood, there is wide support for the direct inhibition hypothesis which posits that: auxin from apical buds travels down shoots to inhibit axillary bud growth, thus promoting tip growth and restricting lateral branching; cytokinin moves from the roots into the shoots, eventually promoting lateral bud growth.

Here is a link to a page on the BBC’s Bitesize site website covering the roles of auxins and cytokinins: https://www.bbc.co.uk/bitesize/guides/z ... revision/1.

So, burning the leaves on a eucalypt seems to change the balance of auxins and cytokinins in the tree, causing it to give priority to back budding over tip growth.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by Watto »

Thanks Phil, I think I will give this technique a go during summer on one of my "troublesome" gums.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by PeterH »

Doesn't cutting back the tree do the same thing. Save on matches or gas.
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Re: Eucalypts as bonsai: a summary of AusBonsai posts

Post by greg27 »

PeterH wrote: July 30th, 2021, 8:16 am Doesn't cutting back the tree do the same thing. Save on matches or gas.
I was wondering this too. Most eucalypts have epicormic buds that are able to withstand damage by fire, but I haven't read anything that indicates that damage by fire does a better job at promoting back-budding vs tip pruning / normal defoliation.

I might experiment with this on my river red gum forest at some point - I'll burn the leaves of half and then just defoliate the other half with scissors and compare the regrowth.
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