The end of spring repotting?

[isid]

In Japan, at least in the warmer regions, the differences between spring and summer are becoming less pronounced. More and more bonsai growers are now avoiding repotting in spring, they claim that in spring the tree does not have time to strengthen before the first heatwave. Thus, repotting in September seems to be becoming the norm. What do you think?

 

[Paradox]

In Japan, at least in the warmer regions, the differences between spring and summer are becoming less pronounced. More and more bonsai growers are now avoiding repotting in spring, they claim that in spring the tree does not have time to strengthen before the first heatwave. Thus, repotting in September seems to be becoming the norm. What do you think?

If in the warmer regions, the winter is also either 3 or 4 months later and/or very mild and never experiences temperatures below freezing or below 40F really, fall repotting can be ok. Though I have to wonder if spring repotting can still be done but earlier than in the past because it would seem late winter/spring might be earlier as well.

Also while fall repotting might be ok for some species, others might not respond well

 

[isid]

Also while fall repotting might be ok for some species, others might not respond well

in this video, he speaks mostly for prunus Mume and Pines

 

[rockm]

Do you live in Japan? If not I wouldn’t be quick to copy. I live in an area that gets summer heat beginning in May and we have 90f days well into October. We had a Halloween ten years ago at 90f.

I repot when the trees need to be repotted. That depends on the weather EVERY SEASON not just because average temps are warming FWIW this past August here was one of the coolest on record, which goes to show what happens in Asia doesn’t necessarily translate in North America (or Europe)

 

[Jetson1950]

Also remember trees do their thing based on length of days, not just temperatures. They are a lot smarter than we are when it comes time to change their growing timing. Sometimes they get fooled by late or early seasonal changes, but most of the time they are dead on. Here in the south, you know spring is here when all the oak trees start their new flush of leaves. That could be late February or maybe almost April.

 

[isid]

Do you live in Japan?

no I live in Corsica which is also quite a hot place. Last year I did (in emergency) some repotting of local essence in mid august, and surprisingly it turned well for all of them (olive-Arbustus unedo-Myrtus communis- Pinus halepensis)

 

[Bonsai Nut]

When I lived in Southern California I would repot my conifers in December for that very reason - to allow them to get established before the heat of the following summer. But we did not have a real winter - ie no temperatures below freezing.

 

[BrianBay9]

When I lived in Southern California I would repot my conifers in December for that very reason - to allow them to get established before the heat of the following summer. But we did not have a real winter - ie no temperatures below freezing.

Yes, I repot starting in December, continuing through February. Perhaps more extreme climate than BN's SoCal, but still haven't seen a hard freeze since I moved here.

We teach beginning bonsai classes at the Clark Bonsai Museum once a month, all year. We use 1 gal junipers and small boxwoods as starting material. They get repotted and worked pretty hard, and do fine even in our hot summers. Just to say, like everything else, when you repot "depends" on species and circumstance.

 

[rockm]

Trees EXITING dormancy in the spring rely on soil temperature not day length. Deciduous trees can overwinter in complete darkness. That is why it is important to protect the root mass from warming in the spring as protect them from cold in the winter. Since they’re in containers temps in the soil will rise and fall much more quickly than the actual ground.

Soil temperature in the ground rises very slowly and trees roots don’t react as quickly to quick sudden warms ups followed by freezing. Not true of bonsai. Particularly over-sheltered bonsai. A warm day or two in February can push bonsai to open leaf buds. Once that happens the tree loses almost all of its protections against freezing

 

[proninyaroslav]

That is why it is important to protect the root mass from warming in the spring as protect them from cold in the winter.

I wonder how harmful such fluctuations are, especially in February, when the sun heats the tree during the day, and in the evening it cools down sharply, and how to protect trees from them?

 

[rockm]

I wonder how harmful such fluctuations are, especially in February, when the sun heats the tree during the day, and in the evening it cools down sharply, and how to protect trees from them?

Depends on sun exposure , temperature changes, etc. I keep some trees in cold pits mulched with a lean-to roof to block southern sun. I also have garden bed situated so they don’t get much direct sun exposure in the afternoon.

Still February and March can be problem months as temperatures rise and fall. Sometimes dramatically

 

[Paradox]

I wonder how harmful such fluctuations are, especially in February, when the sun heats the tree during the day, and in the evening it cools down sharply, and how to protect trees from them?

My cold frame is on the north side of my house so it is less subject to temperature variations from the warming of the sun. As @rockm stated, the ground warms up much more slowly. All of my trees are kept on mats on the ground in the cold frame. The cooler ground along with being on the north side of the house can mitigate spring variations

 

[Wulfskaar]

I've done most of my repotting in Feb-April. It doesn't work with coast live oaks for me, so this winter, I'll be repotting a few oaks in December-January. They start putting out new growth in January. Maybe a couple of my pines too? For my deciduous trees, I've been just watching the buds for when to repot, and those usually come out in March-April and sometimes May. My climate is very mild and very steady. It's interesting how little variation of many factors are required for trees to react.

 

[BobbyLane]

I did two Beeches at the back end of Aug. Doesn't look like they even noticed.

Post in thread 'Fagus Sylvatica Tree'

Aug 24, 2025

Did a little late summer rootwork.
The air layer was really good to me. Nice set of healthy roots here. Removed all the sphagnum moss from under the tree. Its been placed back in the same container. But on a board so the roots can really spread out and contribute to dragging the base out. There's a slightly heavy root on the left and a thinner one directly underneath it, out of view. I contemplated removing the heavier root but instead reduced it closer to the trunk, it seems to be contributing to widening the base so will access it in a year or so. Next time ill likely go a bit harder on...

• BobbyLane

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[stav121]

Living in Greece where the climate is very temperate I tend to sometimes repot healthy young trees in early September without any issue. I still prefer early Spring reporting for most of my trees, but Autumn reporting has never killed a single tree for me.

I reported an Apricot and an Oak just last week and didn't even seem to care at all.

But keep in mind that we have nearly two more months of growing season here, if we had real Autumn and Winter I am not sure that I would do it with much confidence.

I still believe that early Spring is the best way to go. I only do Autumn reporting just to save some time because the window between Late Winter and Early Spring here is too small - blink once and all your trees have woken up. If you have too many and not enough time you might end up not repotting some for the season at all.