Repotting: Spring vs. Summer vs. Fall vs. Winter

[Gabler]

When I was a kid, my dad taught me the best time to transplant a tree is in the middle of winter, when the tree is asleep. In my mind, I rationalized it as similar to surgery on a human. I’d rather be asleep/unconscious. Of course, he was speaking of trees in the ground where the roots would be protected from frost.

When I bought a book on bonsai trees when I was eleven or twelve years old, the book insisted there is a narrow acceptable window for repotting just as the tree is beginning to wake up in the spring. That’s proven to be the conventional wisdom amongst bonsai practitioners.

Subsequent books mentioned a caveat: that azaleas get repotted in the summer To promote bloom. The books alluded to special care for the summer-repotted trees, but didn’t offer much insight into what that might entail.

Then I learned that it is acceptable also to repot in the fall as a tree is going dormant, but before there is a risk of a hard freeze. I tried it myself and observed that the tree was weaker in spring but stronger by summer, though I’m sure results vary wildly between species and climates.

Lately, I’ve seen more frequent recommendations for summer repots, including for pines and maples. While I suspect that summer repots are not wise in a particularly hot and dry climate, are there advantages in certain climates? With certain species? With certain stages of development? Would someone with more experience please weigh in?

 

[HorseloverFat]

When I was a kid, my dad taught me the best time to transplant a tree is in the middle of winter, when the tree is asleep. In my mind, I rationalized it as similar to surgery on a human. I’d rather be asleep/unconscious. Of course, he was speaking of trees in the ground where the roots would be protected from frost.

When I bought a book on bonsai trees when I was eleven or twelve years old, the book insisted there is a narrow acceptable window for repotting just as the tree is beginning to wake up in the spring. That’s proven to be the conventional wisdom amongst bonsai practitioners.

Subsequent books mentioned a caveat: that azaleas get repotted in the summer To promote bloom. The books alluded to special care for the summer-repotted trees, but didn’t offer much insight into what that might entail.

Then I learned that it is acceptable also to repot in the fall as a tree is going dormant, but before there is a risk of a hard freeze. I tried it myself and observed that the tree was weaker in spring but stronger by summer, though I’m sure results vary wildly between species and climates.

Lately, I’ve seen more frequent recommendations for summer repots, including for pines and maples. While I suspect that summer repots are not wise in a particularly hot and dry climate, are there advantages in certain climates? With certain species? With certain stages of development? Would someone with more experience please weigh in?

I am LESS experienced than you... but I'll participate..

I think, conditions and personal preference weigh in, heavily, as well... along with optimal growth timing.,

I believe, that in all actuality, you COULD repot a tree WHENEVER... as long as you are familiar WITH and able to provide the appropriate aftercare.

There are just times of the year that this process operates MUCH smoother.. with "nature" being able to HANDLE more of said aftercare.

 

[rockm]

On the maple thing. Yeah, you can repot in EARLY summer, BUT there are some important details--the leaves have to be "leather hard" or mature. Root work can't be as aggressive as in spring. Any anyone who "recommends" summer repots for maples as a primary season doesn't know what they're talking about.

Additionally, all of this depends ON THE EXPERTISE of the repotter. Spring is the most reliable, safe and effective season to repot temperate zone deciduous trees and mostly pines. The period provides the longest recovery period and weather that is good for maximum growth. Summer, fall and winter all have limited windows of opportunity, but they can also come with a steep price. Extreme temperatures, from freezing to extreme summer temps that slow or halt growth (limiting recovery) Fall presents problems of overwintering trees with reduced roots and big wounds that will sit in hard weather for months with no chance of healing.

Understanding all of that and how to minimize the impact of less-than-optimal repotting is learned over years. And BTW, a rule of thumb for repotting in summer, fall and winter,--just because you CAN, doesn't necessarily mean you SHOULD...

 

[Gabler]

Thanks! I have no intention of repotting outside of spring in the future, but I like to understand why we repot in spring, and the more opinions I get, the more nuanced that understanding becomes.

 

[sorce]

We all long for spring.

Bonsai is all about tree and pot.

Yesterday, I thought, this is probably the only reason we Repot in spring.

Seems it is safer above about 41° latitude to Repot in summer due to the longer day lengths to allow for recovery.

98% of book people having x% of success repotting in spring doesn't mean the other 2% isn't paying attention.

It's a small hole to squeeze through to actually "get it".

Walter "gets it". Pays dem tentions like they work for him.

Walter can Repot in Summer because he doesn't do the other 36 stupid things people do, the trees are just that much healthier.

I have 0 trees that were ever repotted in spring, of hundreds.
Nothing summer repotted ever died, not even almost.

For me, reading the situations.....

You can spend 90% energy moving things from here and there, "2 stepping", saving a day that never needed to be saved.
Or you can spend 0% of energy just not giving in to the impatience brought on by our longing for spring.

Meh. ... everything is a used calorie for me lately.
No way in hell I'm working 80 hours just to earn enough money to recoup the energy spent on spring repotting. I'd rather be fishing.

Sorce

 

[dbonsaiw]

just because you CAN, doesn't necessarily mean you SHOULD

Words to live by.

Picked up some trees at a local bonsai shop over the weekend and mentioned spring repotting. They looked at me like I was from mars and told me to repot in the summer.

As a newbie, and with all the different advice out there, I try to boil as much down to concepts as possible and work from there. Trees have a seasonal cycle. In the fall, they are getting ready for dormancy and storing their energy. Doing work now may force your tree to expend energy on new growth that cannot survive the winter (it hasn't hardened off). Winter work exposes your tree to injury that it has no way of healing as it is in dormancy - you run the risk of die back and infection. I am no expert so don't take this as Gospel, but early spring appears to be an ideal. The tree is coming out of dormancy. It has plenty of reserves and can handle major work. I will do heavy root pruning and trunk chopping together at this time. This is especially true for maples. Once the buds break in spring, the roots have given up a lot of their reserves and requires photosynthesis from the leaves to replenish them. If you allow the tree to expend its energy and then deprive it of the ability to produce more by decimating its roots and cutting off its foliage, the tree will suffer and potentially die. About 2 months after bud break, the tree has replenished its energy and there is a second opportunity for work to be done.

I understand that early spring work produces more vigorous growth and larger internodes. Summer work produces less vigorous growth and smaller internodes.

What I have learned from all the conflicting advice on various bonsai topics is that, although some people can just be wrong, many opinions are sound even if conflicting. There are few absolute answers. Instead, most options provide a trade off - pros and cons - and the practitioner needs to perform his own analysis on which benefits are being pursued and how to handicap for the negatives. Case in point, both Sorce and Rockm have extensive experience and the trees to prove it. If one of them was clearly wrong on this issue, that would surely not be the case.

The questions really boil down to (i) what are the pros and cons of early spring work vs. summer work. And once you have made a decision to go with or the other, (ii) what should I do to handicap for the cons presented by the choice made.

 

[rodeolthr]

FWIW, for me, living in the Pacific Northwest, I do all of my repotting in autumn.....usually late October thru November. Trees will be heavily cut back and roots reduced, especially if they are going into bonsai training pots. My trees then also suffer the injustice of sitting out in the rain all winter and usually being frozen solid for 2 weeks. Oddly, they don't ever seem to suffer and are typically leafing and ready to sell by mid April. I'm in zone 8, so it definitely influences what I'm able to do

 

[rockm]

I really don't get the mindset that Spring repotting is not great because it's seen mostly traditional. I have a feeling that the rise of alternative repotting seasons are one of those obstinate Western bugaboos about rules. "They say I GOTTA do it in spring. THEY cain't make me. Ima do it in August just because I HATE RULES."

I know folks won't like that and will deny it, but I do think that's part of it...I don't see many Japanese growers advocating for summer or fall repotting. I see them using those timeframes as a fall back if they miss the spring window...

 

[Wires_Guy_wires]

I repot in spring, and I don't spend a joule of energy on summer repotting. Gotta keep myself warm in spring, so best keep moving. In summer it's too hot and pressing to do heavy work.

The trees don't seem to care for a couple late freezes.

I work 5 days a week, so I can't do the constant watering thing in the summer. It'd be a waste of trees and worries.

I also repot in fall and winter. Did the two-step once and then figured that my trees are native. They know when to do what.

The key is knowing the climate, knowing the plants and their status.

I stand opposite to sorce on the subject. Because we lead different lives in different settings. I feel fine to disagree on the matter. My trees do well, his probably too. Whatever works!

 

[Nybonsai12]

Lately, I’ve seen more frequent recommendations for summer repots, including for pines and maples.

Anyone can recommend anything. Maybe it’s worked well for them. Doesn’t mean it will work well for you. My advice to you is find somebody whose trees you like and follow their guidance.

I repot in spring and haven’t ever had issues.

 

[Shibui]

Down here we found that Australian native trees actually prefer repot in warmer weather. Many trees repotted or transplanted at the traditional time of winter or early spring just die soon after. The same species don't even pause when chopped and root pruned in summer when they are in full growth mode.
Tropicals also appear to prefer warm weather repotting and I've successfully transplanted azaleas all times of the year, even hot summer.
I have experimented with repotting and transplant traditional deciduous species in summer. The vast majority (mostly younger specimens) have survived these trials but most look really bad or drop all leaves for a few weeks while they make the adjustment.

While I suspect that summer repots are not wise in a particularly hot and dry climate

I've heard this but mostly from older traditional growers who have never tried it because the concept frightens them. Not sure what your concept of 'particularly hot, dry' is but for the last few years I've experienced a week of 40C+ temps right after repotting (Aussie native) trees but those trees grew just as well as others that were not touched.

Certainly the widows are much broader than we've traditionally been taught but those windows are also likely to be influenced by many factors like climate, location, care and species.
Best avenue to learn things is trial and error. Start out with expendable trees but also don't draw conclusions on a single event because unexpected factors sometimes skew the results.

 

[BeepBeepBonsaiSheep]

Where I am in the desert, a mid summer repot will prob kill. The whole month is 100+ temps

However, I’m going to experiment this summer with a repot or two just as the monsoon season comes. Lower temps and once we get the moisture, humidity will be a little higher than normal, plus the added benefit of getting clouds and some rain

 

[HorseloverFat]

Where I am in the desert, a mid summer repot will prob kill. The whole month is 100+ temps

However, I’m going to experiment this summer with a repot or two just as the monsoon season comes. Lower temps and once we get the moisture, humidity will be a little higher than normal, plus the added benefit of getting clouds and some rain

Even round here, if I'm repotting in summer.. trees go in shade the first 4/5 days.. then "Bright Shade" for roughly a week.

 

[Paradox]

I repot everything in the spring. Some species I have repotted in summer successfully, but Ive also had some die from it. The trees of those species that I have repotted at both times always survive and recover better in the spring.

 

[Deep Sea Diver]

Mostly whack out here. I’ve been know to repot most times of the year from Feb-Sept… even bare root. Just need to remember for the outliers all things in moderation… But it depends on the tree, heath, weather forecast, availability to be around to monitor their status.

cheers
DSD sends

 

[BeepBeepBonsaiSheep]

Even round here, if I'm repotting in summer.. trees go in shade the first 4/5 days.. then "Bright Shade" for roughly a week.

Is “bright shade” morning sun?

 

[HorseloverFat]

Is “bright shade” morning sun?

Bright shade is indirect or "filtered sun", in MY book.

 

[0soyoung]

Trees never die when repotted in spring.
We all know that .

 

[Shibui]

Trees never die when repotted in spring.
We all know that .

'Never' is very definite? I've had occasional losses even with spring repot and more than occasional deaths of Aussie natives from early spring repots way back when we did not know better.

 

[Gabler]

'Never' is very definite? I've had occasional losses even with spring repot and more than occasional deaths of Aussie natives from early spring repots way back when we did not know better.

The eye roll emoji indicates sarcasm.