Late summer repotting

[Forsoothe!]

Not only is energy divided in spring, but weather is getting hotter, worse, and as many of us know, early heat can be just as, or even more fatal then a late frost.

Sure you expose the canopy to full sun after late-summer repotting. Temperatures will go down quickly , days are shorter. The full sun on mature foliage will create energy to get lots of new roots quickly. The evaporation is there, but it's getting better every day.

Look at this Latitude-Time chart of the intensity and duration of sunlight. At Detroit's 42.6° latitude April 1st is just beginning intense sunlight, and August 1st intensity is high but diminishing. I store & start all my JM in full sun and move them to partial sun by June 1st. They like sun, but intensity and duration matters greatly. The intensity and duration of sunlight available from August 1st-on is just the kind that mature leaves need, not too intense and diminishing, and not too long and diminishing. The intensity in August is about the same as April/May, a period where we get great growth, but no crispyizing of edges.

 

[Forsoothe!]

And one caveat: after extensive root work, never, ever, let the tree suffer from drought for one minute. Too wet for a few hours is much less damaging than too dry to support the foliage. Any day it doesn't rain, I water at least once.

 

[Walter Pall]

Forsoothe,

This chart can be very useful. I am afraid the mark for Detroit is not correct. If I read this correctly Detroit is on 42 and you have done the black line at about 35. If I am correct then the blue line above your black one should be close to reality. Then the next blue like above it is for Munich, Germany which is at about 48 latitude.

If you then take mid-August and draw a vertical line down to the two horizontal lines you can see that Detroit and Munich are about a week apart - meaning it is cooler in Munich at middle of August when I have optimal time and it is a bit more sun still in Detroit.l This could mean that Detroit folks should wait a bit and go to August 20 or so to do late-summer repotting.

It also shows that there is about 8 weeks at least where it should be warm enough for the trees to still grow after mid-August in both places. Less in Munich than in Detroit.

if this is correct then everyone can find out about their latitude and find how far away they are from the situation in Munich (latitude 48) at mid-August. Then they can draw their conclusions from there.

Basically it shows what common sense tells us anyway. The more south the later you should do late-Sumer repotting and the earlier you can do spring repotting. The more north the earlier you shod do late-summer repotting and the later spring repotting.

This explains why in central Norway. they collect Scots pines in the bogs around end of July and get away with it. Oslo is at 59 latitude and about two and half weeks away from Munich according to the chart.

 

[sorce]

Interesting.

Sorce

 

[leatherback]

At Detroit's 42.6° latitude April 1st is just beginning intense sunlight, and August 1st intensity is high but diminishing.

I think this graph is mis-interpreted. It is an accumulated radiation per day, not the absolute intensity. Else, one would see more intense sunlight at the poles in peak summer than at the equator, which of course is not true. Only because of the day length the total wattage per surface area is high at the poles, not because of light intensity.

 

[Forsoothe!]

OK Walter, you've forced me to do it right. The graduations are 10°, but here's a better chart. (Still pretty rough).

 

[leatherback]

One again, I would not recommend using the graph in such a way. This is energy levels that hits the atmosphere over a 24hr period.

Being further from the poles mean longer summer days, and shorter winter days heavily influencing the accumulated colar irradiation for that day. Not per se meaning you have more energy per irradiated time unit (Say, per second). If in mid-summer you move from norway to the tropics, you will still get a heavy sunburn because direct sun intensity is much higher.

Furthermore, this is top of atmosphere. At higher latitudes the path for sunlight through the atmosphere is much longer than at the tropics (Lower sun angle), resulting in a reduced intensity of sunlight reaching the surface.

The graph is nice for energy budgetting of the earth as a system. They give an indication of the amount of energy available at the earth's surface but do not tell you how intense the sun at the surface will be.

 

[Gustavo Martins]

From my personal observation I created a ‘rule’ to protect my Japanese maples from sunburnt which is: when daytime temperatures rise above 21C I move them into the shade. This means that they stay in shade here from late May through late September. They only get maybe 1-2 hours of direct sun until 10 am. I still get some crispy leaves but nothing special compared to the first year. Something like this may also work for repotting...

 

[Rafael Najmanovich]

In the last week or so I have been repotting nursery stock: chinese junipers, mugo pines, colorado blue spruces, an eastern hemlock (Tsuga canadensis) and a smokebush in full leaf and still have eastern white cedars (thuja) to repot. All root bound in nursery containers and old soil to their first bonsai training pot. I performed the same as severe as necessary root work that i would have in spring. Of course showing a recently repotted conifer is not proof that it didn't impact the trees health but I can show you as proof the smokebush and the leafs did not for a moment show any sign of impact from the root work. In the attached photo the hemlock next to the smoke bush was also repotted (from a 3 gal container into this very small pot a few days ago).

 

[Rafael Najmanovich]

OK Walter, you've forced me to do it right. The graduations are 10°, but here's a better chart. (Still pretty rough).
View attachment 257482

awesome work!

 

[leatherback]

 

[sorce]

Hey aaaahhhh....

Even a "correct" colorful graph is still a waste of time IMO.

What is this proving or disproving?

We need a SIMPLE way to understand who can repot when.
A simple point system perhaps?

There is more pertinent knowledge to be had from @Gustavo Martins line of thought.

It's simpler than graphs which the trees don't understand.

Sorce

 

[crust]

This quote does not make any horticultural sense at all. I don't care where you live. Who are the people you speak of that do nothing?

Repotting is a lot of work and a pain, one gets overwhelmed, especially in the spring and then repotting gets neglected, trees decline. This has been my story for 4 years. Trees have died.

 

[Matt H.]

it sounds more like you don't have one

And you do realize that there is a search function on this forum and on the internet? you often present your view, whether about soil, pruning, repotting, etc. as though it were in direct opposition to 'traditional' or 'japanese' ideas. At this point, whenever somebody reads "forget everything you know about..." they must inevitably hear your voice in their head!

Who are you to post this? What are your credentials? Walter's are well known and he could not have been more clear in saying that what he does is right for his tree in that place and time. He is not trying to convince anybody of anything. He is simply showing his technique in a specific instance. I for one appreciate this. If you are not able to understand what he is saying then why are you posting???

 

[MrFancyPlants]

In the last week or so I have been repotting nursery stock: chinese junipers, mugo pines, colorado blue spruces, an eastern hemlock (Tsuga canadensis) and a smokebush in full leaf and still have eastern white cedars (thuja) to repot. All root bound in nursery containers and old soil to their first bonsai training pot. I performed the same as severe as necessary root work that i would have in spring. Of course showing a recently repotted conifer is not proof that it didn't impact the trees health but I can show you as proof the smokebush and the leafs did not for a moment show any sign of impact from the root work. In the attached photo the hemlock next to the smoke bush was also repotted (from a 3 gal container into this very small pot a few days ago).

Any chance you could start a separate thread on your hemlock? I’m always searching for experience/advice.

And, props to everyone for getting the thread back on topic. There are some great insights here.

 

[SantaFeBonsai]

If you can repot in late summer and based on the graph I should await until sept 15 @32deg lat then separating an arakawa airlayer and doing the ebihara board technique shouldn’t be an issue, right?

 

[Dav4]

If you can repot in late summer and based on the graph I should await until sept 15 @32deg lat then separating an arakawa airlayer and doing the ebihara board technique shouldn’t be an issue, right?

Let us know... I'd gladly spread the spring re-pot season into late summer to avoid the bonsai shuffle!

 

[Cosmos]

It’s fantastic that this thread is changing some people’s mind and pushing them to experiment. This is what this forum is for, not drama about silly stuff.

 

[Walter Pall]

I think this graph has some value. It is top of atmosphere, sure. Imagien thre wer no cluds or mist. Then

If you can repot in late summer and based on the graph I should await until sept 15 @32deg lat then separating an arakawa airlayer and doing the ebihara board technique shouldn’t be an issue, right?

Sounds right to me. Make sure you get frost free winter storage.

 

[leatherback]

I think this graph has some value. It is top of atmosphere, sure. Imagien thre wer no cluds or mist. Then

top of atmosphere AND over a 24hr period. So not taking into account different solar intensity.
The graph would have you believe mi-summer sun at the poles is stronger than sunlight in the tropics which is nonsense.

Anyway. Seems like I am only talking to myself here. Everyone, have fun with the graph. Just realize the results might be very different than expected. I will stay out of the graph discussion, unless invited back in.