Autumn repotting of very northern trees?

[Grant Bowie]

As you may know I came to the conclusion a few years ago that, in Canberra, it was best to repot all conifers(except Cedrus atlantica) in Autumn.

This was reinforced by the death of a Scotts pine on which I did a hard root prune in spring about 5 years ago. The tree initially put out lots of new growth, then paused and really went off. I investigated a few weeks later and found the root system had in effect rotted off. I repotted it into pure sand/fine gravel. I pulled off all the rotted root system and trimmed. The tree seemed to stabilise but about a year later it did go off permanently.

I read somewhere at the time that Scotts/Mugo pines put out most/all of their root growth in Autumn. (Can anyone find/confirm this for me?)

This made sense to me; a tree growing at high altitude in extreme cold or even lower altitude with heavy snow/frost would have its roots frozen/very cold during springtime; so the tree had adapted to putting out foliage growth in Springtime and then put out new roots in Autumn when the weather was mild and the soil warm. In effect the new growth in springtime is living off the vigour in the wood and the vigour supplied by the roots in Autumn.

So, in Bonsai terms, if we trim off the roots in spring the tree cannot/does not replace roots till Autumn. Therefore it would be best to root prune in Autumn rather than Spring. The Pine I had trimmed sat in wet, cold soil for months with no new root growth and then failed.

(NOTE. This may not be applicable in your climate or with all cold climate trees.)

Does the above reasoning sound "sound" to you?

Comments please.

I will make a comparison to another tree as well soon.

Grant

[Jarad]

Hi Grant,

I'm a pretty massive noob, but there were a couple of youtube videos floating around that were about the growth habits of different pines, you've probably seen them already, but I will post them anyway.

Here's the second page of the thread where the videos were posted by Dario:
viewtopic.php?f=131&t=15503&start=15

And here are the links to the videos he posted:
https://www.youtube.com/watch?v=Yn1FiRw2JBo
https://www.youtube.com/watch?v=-1Y6j2wgI2U

I hope this helps.

[shibui]

The death of 1 scots pine is not really conclusive proof that spring repotting is deadly for the species. Last winter I dug 17 Juniper chinensis from the grow beds. All were root pruned pretty much the same. Aftercare and potting was the same for all but 13 grew steadily and recovered well. 2 took ages to recover and have only just recently felt stable in the pots. 2 turned yellow and died a couple of months after potting up. Does this result mean that winter/spring root pruning of juniper is good or bad?
I wonder why the Japanese growers seem to insist on spring repotting. Surely if there was an advantage to autumn repotting of conifers some Japanese growers would have discovered that by now?

I read somewhere at the time that Scotts/Mugo pines put out most/all of their root growth in Autumn. (Can anyone find/confirm this for me?)

I've said before, just because something is written does not necessarily make it true, even if it agrees with your theories.
Alex George, in The Banksia Book states that banksias produce top growth in spring and root growth in Autumn but does not tell us how he came to that conclusion. When I plant banksia seed in spring roots grow as well as the shoots so I know that young banksias do grow roots in spring. I haven't uprooted an older plant to check whether that changes with age but can't see why it would.
I assume that plants grow whenever conditions favour growth.

I do believe that autumn repotting is viable and may even be preferrable but maybe we are looking a bit deep for something to justify breaking from tradition?

[treeman]

I agree that Autumn repotting is a good idea.....in mild climates like Australia. Autumn repotting in very frosty northern hem zones is highly risky as a tree with freshly cut roots hit by 6 months of freezing weather is bound to suffer. Hense the Japanese recommendation to take trees under protective shelter if repotted in autumn.

But in Australia, not only does it take some of the pressure off spring repotting, but for flowering sp for example, they have a long period to develop new roots and become established before the following spring. Crab apples are a classic example. Flowering Apricot not so much as it flowers in winter.

As for pines, I think it would be quite advatageous to repot in autumn so they can get away with an uniterrupeted start in spring. I have a few scotts pines and have not tried autumn repotting but I can see it has it's merits. But there is no need to stop at scotts pines. I think any pine and in fact most cool climate trees could easily be repotted in autumn in this country with good results.
As long as it is before very cold weather or in my case before May. What about Pinus radiata? It comes from a mediterranean climate as is naturally dormant in summer. Perhaps autumn repotting is best for this tree too (if you bother to grow them)

When I had a retail nursery, we would get delivery of our bare root stock in mid June and heal them in sawdust. Regradless of the temp, they put out long white roots within days.

[RogerW]

Don't forget that Grant lives in Canberra, where we get on average 160 frosts each year. This is similar to the climate in the Northern Hemisphere.

[treeman]

Don't forget that Grant lives in Canberra, where we get on average 160 frosts each year. This is similar to the climate in the Northern Hemisphere.

Nowhere near it!

[Grant Bowie]

Don't forget that Grant lives in Canberra, where we get on average 160 frosts each year. This is similar to the climate in the Northern Hemisphere.

Nowhere near it!

Correct,

In very cold northern areas where bonsai are grown spring is best.

Canberra is a bit in between, hence the problem or opportunity.

Grant

[kez]

Also I think its worth mentioning that most of the japanese methods would relate to white/black pine. I don't know whether they would bother playing with Scots or mugo as they have the best white/black material in the world.

Perhaps they haven't needed to experiment with the other cold climate pines. I know the white is of the 2 a cold climate pine but how does Japan's winter compare with what mugo or scots pines deal with?

I think that the theory at least behind this notion is logical, and it looks like we will be the benefactors of someone else's leg work here, I say great work Grant for trying to write Australia's rules!

Eagerly awaiting the outcome

Kerrin

[Grant Bowie]

Anyhow,

As i said I now pot every conifer (except Cedrus atlantica)in autumn, including Radiata pine.

My other tree that caused me to think was a Beech. Deciduous tree from central Germany right up into the Fiords and forests of Norway. Very cold country indeed. I have been in Germany in winter at about -15 in mid day. Nothing like Canberra.

I repotted a Beech last spring (not a major prune but just a new pot) and it dutifully put out strong spring growth and then stalled; leaving a lot of bare branches. I kept an eye on it suspecting root rot and kept it on the dry side and treated with Fongarid.It eventually put out some weak growth on all the remaining branches and survived OK. The new growth however had that look where it was affected by root rot(small leaves and very pale and see through). I thought the pot may be at fault with a pooling of water.

Anyhow I repotted it last week in full leaf, inspected the pot and it was OK, so I started wondering if this tree also put out strong root growth later in the season, rather than early spring.

Please note; some trees I only have one or two of each and so I end up experimenting on some of my best trees.

Anyhow, just some stray thoughts I am putting down, not proving a thesis, and interested in thoughts.

Grant

[Grant Bowie]

Also I think its worth mentioning that most of the japanese methods would relate to white/black pine. I don't know whether they would bother playing with Scots or mugo as they have the best white/black material in the world.

Perhaps they haven't needed to experiment with the other cold climate pines. I know the white is of the 2 a cold climate pine but how does Japan's winter compare with what mugo or scots pines deal with?

I think that the theory at least behind this notion is logical, and it looks like we will be the benefactors of someone else's leg work here, I say great work Grant for trying to write Australia's rules!

Eagerly awaiting the outcome

Kerrin

Japanese White pine were growing OK in Shanghai which can be almost tropical for part of the year, but their natural climate is very cold country probably similar to Scots and mugo.

Grant

[MoGanic]

Grant,

Thanks for raising such an interesting topic.

From what I know, most trees roots grow in soil temps between 21-24 (roughly?) degrees Celsius. These temps are the key factor here, and the season in which these temps occur are purely incidental.

For example, in a particular region, those temps may be reached in Spring - hence spring repotting. Other regions may reach those temps in Autumn - hence autumn repotting.

It's not about what season, rather what temps are best for repotting. Just comes back to basic biology of plants and trees.

One thing I would love to know, is do roots grow during the day or night? We all know growth above soil mostly happens at night and photosynthesis during the day in the growing season. But what about roots?

By the way - I am not presenting my theories/observations/info as concrete facts. This is just what I go by. Please don't bite my head off .

Cheers,
Mo


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[Tim.C]

Don't know if this is relevant being in brisvegas. I dug some slash pine and she oaks about a month ago, gave roots a tidy up and potted in 8" pots and they're looking good still. Also repotted and root pruned two Daintree pines about 6 weeks ago. They're still looking good. I don't know much about pines though. Hence digging slash. Trial and error on them before I kill anything decent. Daintrees were a necessity though. Very badly pot bound.

[Grant Bowie]

Grant,

Thanks for raising such an interesting topic.

From what I know, most trees roots grow in soil temps between 21-24 (roughly?) degrees Celsius. These temps are the key factor here, and the season in which these temps occur are purely incidental.

For example, in a particular region, those temps may be reached in Spring - hence spring repotting. Other regions may reach those temps in Autumn - hence autumn repotting.

It's not about what season, rather what temps are best for repotting. Just comes back to basic biology of plants and trees.

One thing I would love to know, is do roots grow during the day or night? We all know growth above soil mostly happens at night and photosynthesis during the day in the growing season. But what about roots?

By the way - I am not presenting my theories/observations/info as concrete facts. This is just what I go by. Please don't bite my head off .

Cheers,
Mo


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No problem.

I wonder when roots grow in areas that never get near 21 to 24 degrees ground temp? Must grow at lower temps I would think.

Grant

[MoGanic]

Grant,

Thanks for raising such an interesting topic.

From what I know, most trees roots grow in soil temps between 21-24 (roughly?) degrees Celsius. These temps are the key factor here, and the season in which these temps occur are purely incidental.

For example, in a particular region, those temps may be reached in Spring - hence spring repotting. Other regions may reach those temps in Autumn - hence autumn repotting.

It's not about what season, rather what temps are best for repotting. Just comes back to basic biology of plants and trees.

One thing I would love to know, is do roots grow during the day or night? We all know growth above soil mostly happens at night and photosynthesis during the day in the growing season. But what about roots?

By the way - I am not presenting my theories/observations/info as concrete facts. This is just what I go by. Please don't bite my head off .

Cheers,
Mo


Sent from my iPhone using Tapatalk

No problem.

I wonder when roots grow in areas that never get near 21 to 24 degrees ground temp? Must grow at lower temps I would think.

Grant

Good point. More research required! I wonder if there are any biologists on here that could help.

Mo


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[Grant Bowie]

Anyhow it is working with natural tendencies/evolution of trees and then doing bonsai techniques on them in our various climates and making them survive.

One size certainly doesn't fit all,

Grant