Summer Repotting

[Paradox]

With the exception of tropicals, I have only repotted mugo and scots pines during the summer.

I have repotted mugo pines in the summer with success. However, in my experimentation with them, I have found that while they will do ok with summer repotting, I have had a more vigorous response and faster recovery with a spring repot. I repotted one mugo in the summer one year and it sulked and sulked and just didnt seem happy. Even the following spring it was late to get going but it did eventually. Another mugo I repotted the spring after bounced back faster than the one repotted the previous summer. Different tree, different response, apples to oranges, who knows but the spring repot did much better.

Scots pine is another that some claim is best repotted in summer. With the exception of one tree, every other scots pine I repotted in summer died. Every one I have done in the spring survived the repotting with faster and more vigorous recovery.

Granted my sample sizes arent large either so its hard to draw a concrete conclusion, but in my experience, my trees do better with a spring repot than a summer repot.

Ive had some vigorous debates here with Vance about this as his experience is different. I think he either has me on ignore or just wont respond to any of my mugo and scots pines posts any more because I dont follow his mantra with repotting mugos and scots. I have been told by others that have mugos and scots that they repot in the spring just fine, including Telperion farms, John Kirby, Mark Comstock and others. Mark and John are much closer to my area (Connecticut) than Vance is so I believe it may have to do partly with environmental differences.

I never have denied and wont deny that what Vance does works. It works for him, but it doesnt work for everyone. Many people have tried to repot mugos in the summer and they died, many have repotted mugos in the summer with success. My observation is that the former outnumbers the later, however I will say that there may also be a newbie factor in those observations as many of those were newish people to bonsai.

I once started a thread about mugo and scots repotting but it only got to 3 pages.
There is some documentation in there with my trees

Scots and Mugos Repotting Discussion

Ive started a new thread about this here rather than post in MFray's collection thread and hijack it (sorry MFray). I think this is a worthy discussion. Vance is the undeniable expert when it comes to Mugos in the U.S.. He promotes repotting both species in summer rather than spring...

www.bonsainut.com

 

[Brian Van Fleet]

That aspect of bonsai (proper matching of species and local climate) is not stressed enough. There’s a number of forum members here who live in the Pacific Northwest who apparently don’t understand that species that grow well there don’t like the environment 2000 miles to the Southeast! Lol!!!

Well-stated, Adair. I have long advocated for the concept of growing what grows well in your area. I also tend to avoid wading into discussions where I have limited experience. However, I have offered to grow one of Vance’s mugo pines here, even doing the work when he says to do it. He has not taken me up on this offer. I think that is unfortunate, and perhaps he is concerned for the outcome.

The professionals that I have seen discuss summer repotting typically mention avoiding freezing temps the following winter. Did you consider doing anything different for these trees, or was this more about seeing if you could successfully do summer repot while treating them the same as your other trees?

No, I deliberately subjected them to the same conditions as my other trees of the same species. That was the “control”.

Other....on "Sorce's Center-Point Bonsai Calendar"(coming soon) summer repotting in Bama should take place well after August's full Moon. For the record, these repots were done 4 days before the full moon which is good.

Are you suggesting the outcome would have been different by waiting 4 days? I put the weather almanac on my blog, but not here...this was the weather, and I don’t believe the moon phase would have changed the outcome. I’d be curious to see some results on that variable.

 

[sorce]

decipher your post.

Sorry.

No, you were on point for that moon.
September, October, maybe even November's FM would be equivalent to what I'm finding a good time up here.

I think the most important part of W.P.'s idea, is that weather is cooling.
I don't see Bama cooling in August!

It sucks that this winter sucked, I feel like you would have had great success, according to the maples couple weeks later pics. In my world, that tree survived repot and died over winter. No?

Sorce

 

[Adair M]

With the exception of tropicals, I have only repotted mugo and scots pines during the summer.

I have repotted mugo pines in the summer with success. However, in my experimentation with them, I have found that while they will do ok with summer repotting, I have had a more vigorous response and faster recovery with a spring repot. I repotted one mugo in the summer one year and it sulked and sulked and just didnt seem happy. Even the following spring it was late to get going but it did eventually. Another mugo I repotted the spring after bounced back faster than the one repotted the previous summer. Different tree, different response, apples to oranges, who knows but the spring repot did much better.

Scots pine is another that some claim is best repotted in summer. With the exception of one tree, every other scots pine I repotted in summer died. Every one I have done in the spring survived the repotting with faster and more vigorous recovery.

Granted my sample sizes arent large either so its hard to draw a concrete conclusion, but in my experience, my trees do better with a spring repot than a summer repot.

Ive had some vigorous debates here with Vance about this as his experience is different. I think he either has me on ignore or just wont respond to any of my mugo and scots pines posts any more because I dont follow his mantra with repotting mugos and scots. I have been told by others that have mugos and scots that they repot in the spring just fine, including Telperion farms, John Kirby, Mark Comstock and others. Mark and John are much closer to my area (Connecticut) than Vance is so I believe it may have to do partly with environmental differences.

I never have denied and wont deny that what Vance does works. It works for him, but it doesnt work for everyone. Many people have tried to repot mugos in the summer and they died, many have repotted mugos in the summer with success. My observation is that the former outnumbers the later, however I will say that there may also be a newbie factor in those observations as many of those were newish people to bonsai.

I once started a thread about mugo and scots repotting but it only got to 3 pages.
There is some documentation in there with my trees

Scots and Mugos Repotting Discussion

Ive started a new thread about this here rather than post in MFray's collection thread and hijack it (sorry MFray). I think this is a worthy discussion. Vance is the undeniable expert when it comes to Mugos in the U.S.. He promotes repotting both species in summer rather than spring...

www.bonsainut.com

If I lived in your area, I would follow the advice of Kirby, Comstock, and John Romano.

 

[Colorado]

I was compelled to conduct a similar experiment as a result of that thread. Obviously sample size is too small to make any reliable conclusions.

But I think it all depends on how “drastic” a repot you do. I did an aggressive “spring” repot on a Chinese elm last August and it kicked it almost immediately.

Conversely, I did a couple repots on an Amur maple and a cotoneaster from their nursery containers to training pots and bonsai soil. I just sawed off the bottom 2/3 of the rootball with the intention of going back in for another more invasive repot 2 years later.

Neither skipped a beat. Both were left outside unprotected all winter.

The maple put out 2+ foot extensions this spring before I chopped it:



The cotoneaster is also very vigorous this year.

So, I think it is a matter of degree. Late summer offers an opportunity to get nursery stock out into a training pot with bonsai soil, if one takes a more conservative approach. I also wouldn’t hesitate to do a moderate repot to change the pot or orientation with minimal root work.

But I am not going to be repotting my best trees or performing aggressive root work in summer.

 

[sorce]

sample size is too small

It's a Group effort!
Keep posting useful information!

Sorce

 

[Dav4]

These tridents were chopped last summer then dug and roots reduced in early October. Both budded out and one even grew a bit, but both fizzled once remotely warm weather arrived hear about 2 months ago. The same work done in spring hasn't really set back the others from this batch. Granted, this isn't quite comparable to a mid summer re-pot, but what was done was technically "out of season" root work. Temperatures in mid October were very mild, basically mid 80s F down to mid 70's with no frosts until 11/18/19, and the winter as a whole was mild, so the soil never came close to freezing and was probably above 40 F for most of the dormant season, meaning root growth should have been good. I really expected this to work and can't quite explain why it didn't... and I guess that's the point- out of season re-pots can throw you curve balls that you don't see coming. Anyway, all 3 trees treated this way are firewood now, so I won't be doing this again.

Trident 1 10/10/19


10/24/19, 2 weeks after root work


Today


Trident 2 8/10/19. This one had been chopped in July and was budding back nicely.

Today.

 

[sorce]

Damn! You guys aren't using "crap" material.

You should have went and got some testers from where I shop!

FTR...for me...
Cutting roots so hard must be coupled with a reduction of transpiration. Defoil or heavy prune.

Seems you found initial success, so I still don't want to believe repotting caused the failure.

Sorce

 

[Brian Van Fleet]

Damn! You guys aren't using "crap" material.

You should have went and got some testers from where I shop!

FTR...for me...
Cutting roots so hard must be coupled with a reduction of transpiration. Defoil or heavy prune.

Seems you found initial success, so I still don't want to believe repotting caused the failure.

Sorce

I would highly recommend you read “Bonsai Heresy” by Michael Hagedorn.

 

[sorce]

high

It's one of the first books I've found worth thinking about spending the money on.

Sorce

 

[leatherback]

Maples, elm, zelkova, malus.. I am not concerned repotting when in full leaf. Heck, I repot these when I feel like it. But I admit, these are all in growin out stage: Full of health, juicy and all. I normally do this when a week of rain is expected. Trees generally do not seem to mind.

Prefer repotting in later winter / early spring though. I do summer repots on trees that clearly outgrow the pot or if I am annoyed with them being in the wrong pot.

 

[bwaynef]

Who else has real summer repotting results to share? Photos would be appropriate to support anecdotes. In some climates, I can see getting away with it, but in most cases, I don’t see any advantage to repotting in summer vs. Spring. Interestingly, Michael Hagedorn addresses this topic in his book, “Bonsai Heresy”. Had a chance to start reading it while on vacation this week.

A friend has a Juniper that's special to him for some reason. (Its on his won't sell list at his nursery. I don't know the significance.) He came to me after having let it grow for a couple years and it didn't look good. All the growth was weak and the tree overall was sparse. He suggested maybe cutting it back would prompt it to backbud and regain some vigor. It was in very poor, dense soil. It was also June. I'd heard some talk of folks repotting junipers in summer with good luck ...and this one was weakening every month I checked on it at his nursery. I told him about what I was reading folks were saying about their summer repots and that I think that the roots are where you build health.

We half-barerooted it in the summer of '18. (It would've been the 4th Saturday of June '18. Look that up if you want a date.) I used LaPumAka (figure it out) in equal parts. I used "standard" half-bareroot technique, just as severe as I would have if I'd done it in the traditional spring timeframe. I asked him to site it in the sunniest location, and to double-check that his automatic watering heads were covering the area this juniper was in regularly. It grew well the rest of the year and we noticed backbudding that season. We left it to grow all of '19 and its apparent vigor increased as well. Since it was growing well and backbudding, we had indications it was safe to finish its transition into inorganic soil in late January. The only picture I have of this whole operation is from when I pulled the tree out of the pot then. I was blown away at how nice the rootball was, coming from what was such a weak tree to begin with. The plan for the season was to begin reducing the canopy to further drive energy into the backbuds and thereby compact the tree. Hopefully I'll be able to get back over and help him improve it this year, but at least its health is restored.

As for summer repotting, even though the results were positive, I wouldn't do it as a matter of course. This was a situation where the tree was in decline and something had to be done. Also, the situation is a little different than what I've seen presented (on the first page at least) in that this was a half-bareroot repot.

 

[Arcto]

Thank you @Brian Van Fleet for posting this thread. I enjoy these. Please allow me to introduce my unscientific research to add confusion to this discussion. A Norway Spruce that was a 60-70% bareroot that was taken from a Anderson flat to a bonsai training pot last August. In good health and new growth starting to harden off today.


Small nursery stock Manzanita fully barefooted 2 early Septembers ago. Recovery and growth matches Manzanita I’ve done similar work on in the spring.


Pacific Madrone fully barerooted last September. Recovered and growing strongly.

Arizona Madrone 40% barerooted this spring. Severe shock evidenced by discolored bark and total leaf drop. Some weak growth and buds forming now. But at least a full year lost.

The Madrones were not a good comparison. A native tree here vs a SW native using different root work techniques. As others have pointed out, we can get away with plant murder in the PNW. I have very cool sunny summers and long mild falls. But it’s not all fun and games up here. I’ve been trying to grow out a “Texas shohin” Crape Mrytle like @markyscott. So far, I haven’t come close.

 

[sorce]

But at least a full year lost

You know how they say, "a penny saved is a penny earned"...?

A year lost is a year gained!

That could be the tight growth layer that prevents a branch from breaking in a future accident.

Sorce

 

[Mikecheck123]

There is a thread on here from a couple of years ago where Walter demonstrates doing summer root pruning on a (very expensive) Japanese maple. I'll look for it.

As I understand the theory of why this is better than spring repotting, as long as you don't go crazy (removing say, no more than 20% of the root mass), the tree has enough time to rebuild the roots for dormancy. Then in the spring the tree is even more vigorous because it can expend all the energy on foliage rather than on recovering from a repot.

I did a little experiment last summer, and I have to say that I am now a firm believer. The difference in the springtime foliage was very dramatic.

Here's a comparison pic of the outcomes. On the left is the tree in April of this year (after doing a late July root pruning job). On the right is the tree in April of 2019.

Essentially the late summer root pruning resulted in much bushier, denser foliage. For every branch in the pic on the right, there's about 10 branches on the left. I should mention that those branches in both pictures are exactly the same age because this is my "mother tree" that I keep airlayering stuff off of. (The more I airlayer, the taller it seems to get... hmmmmm.....



Here's a pic of what I did.

Before:




After raking out and pruning off the outer 20% of the roots.




To borrow one of Walter's catch phrases, the tree "didn't even blink" at this procedure.

So I plan on doing it again this year.

 

[Mikecheck123]

Here's the previous thread: https://www.bonsainut.com/threads/repotting-big-maple.35178/

 

[Igor. T. Ljubek]

I repoted an European hornbeam (carpinus betulus), elm (ulmus minor) and a hawthorn (crataegus monogyna) in early September 2019, just about 3 or 4 weeks before leaves were start turning yellow. On hornbeam and elm i did very little root pruning, while Hawthorn was heavily root pruned, because it was collected from nature. All of the trees are growing just fine at the moment, to one's great surprise even hawthorn survived with no dieback. I am gonna repeat the experiment in the end of this summer with another 2 samples. Maybe i just got lucky with mild winter in 2019/2020. I think that repoting too early might cause some troubles. If you are living in a zone 8 or 9 you should repot latter in the summer. Early or mid september, imo. Anyway i still prefer early spring repotting.

 

[leatherback]

Here's a pic of what I did.

To be honest.. I would not call that really repotting. If I repot the tree looses a whole lot more roots, as needed to improve the nebari and remove all roots that are unneeded (Basically, roots older than 6 months add very litte to the tree; Most action is at the youngest tips. Once barked over it is just taking up space in the pot).

 

[sorce]

I reckon it's overly important to note that Walter never removes many roots.

He never experiences the "slow down" due to "too many Roots", which is our US excuse to cut the shit out of everything?

He usually is simply changing aesthetics.

Said Aesthetics are always on point. Never Mounded or inappropriate.

With all the signs leading to "don't cut so many roots", why do we even do it still?

Spring or summer?

Sorce

 

[Colorado]

With all the signs leading to "don't cut so many roots", why do we even do it still?

Spring or summer?

Sorce

Well, Walter’s trees already have impeccable nebari.