Managing Deciduous Bonsai During Warmer Winters

[stav121]

Hello everyone,

I’m starting this thread to gather your experiences and advice on handling warm autumns and winters with deciduous bonsai.

This year has been unusually mild here in Athens, Greece. Night temperatures have rarely dropped below 5 °C, and as of today (11th January), about half of my deciduous trees still haven’t dropped their leaves. Some, like my Chinese Elms and Chinese Quince, haven’t shown any sign of leaf drop at all. Growth has essentially stopped for almost two months, but the leaves remain green. Normally, all my deciduous bonsai are completely bare by this time of year.

How do you handle situations like this? Do you leave the trees as they are, or do you defoliate them manually? Could this kind of warm winter have any long-term effects on the trees?

 

[Bonsai Nut]

I leave them as they are. If they are still green they may in fact still be photosynthesizing.

Every now and then in Southern California I would prune a deciduous tree late in the year, or have to do a late repot that would result in a push of new growth in the late fall. In most cases those trees would skip the winter entirely, maintaining green leaves, and push a new round of growth in the spring as normal. I never had an experience where that happened multiple years in a row, but I can tell you that skipping one winter isn't a big deal. If your tree is a flowering or fruiting species, it might impact that schedule and they might skip their flowers or fruit for a season. Stone fruits in Southern California required a minimum number of "cold degree days" in order to set fruit, and if we had a warm winter sometimes I wouldn't get any plums or peaches. The same might apply to quince... though I don't know.

 

[BrightsideB]

Also like @Bonsai Nut stated. I did a trunk chop on a Chinese elm in fall. It grew a new leader and kept its leaves all winter even though we had temps in single digits. Chinese elm’s are hardcore!

keeping in the shade in the coldest part of your yard will help. Daylight hours is also a signal for dormancy period.

 

[stav121]

I’ve also been wondering whether this could be related to differences in sun exposure since I moved about 8–9 months ago. At my previous place, the trees received only morning sun, with no midday or afternoon exposure. In my current location, the situation is reversed: no morning sun, but strong midday and afternoon sun.

Even so, I’m seeing some extreme inconsistencies. For example, my beech (Fagus sylvatica) shed all of its leaves in October 2025—which is very unusual for my climate—whereas last year (2024) it didn’t begin shedding until late December.

 

[rockm]

I’ve also been wondering whether this could be related to differences in sun exposure since I moved about 8–9 months ago. At my previous place, the trees received only morning sun, with no midday or afternoon exposure. In my current location, the situation is reversed: no morning sun, but strong midday and afternoon sun.

Even so, I’m seeing some extreme inconsistencies. For example, my beech (Fagus sylvatica) shed all of its leaves in October 2025—which is very unusual for my climate—whereas last year (2024) it didn’t begin shedding until late December.

Dormant deciduous tree should ideally be kept in the shade for this very reason. Sun warms soil. Warm soil pushes roots to break dormancy.

 

[River's Edge]

We are having a very warm and wet winter. Many of my Prunus Mume are still in leaf. I do not defoliate in this situation. With deciduous that are in the greenhouse I find it helps to shade the roof of the greenhouse to reduce extra warmth when the sun comes out. Another step is to open the green house frequently during the day for air movement and better control over condensation and excess humidity. For extra rain, tilting pots and protecting under cover is important. I believe the modern terminology is in the presence of an atmospheric river.
As mentioned by others keeping the trees as cool as possible to maintain dormancy without exposing to damaging freeze temperatures.
Long term effects could become an issue if the weather is consistently warmer over a number of winters. One winter is not likely to create long term issues, trees are very resilient.

 

[stav121]

I leave them as they are. If they are still green they may in fact still be photosynthesizing.

Every now and then in Southern California I would prune a deciduous tree late in the year, or have to do a late repot that would result in a push of new growth in the late fall. In most cases those trees would skip the winter entirely, maintaining green leaves, and push a new round of growth in the spring as normal. I never had an experience where that happened multiple years in a row, but I can tell you that skipping one winter isn't a big deal. If your tree is a flowering or fruiting species, it might impact that schedule and they might skip their flowers or fruit for a season. Stone fruits in Southern California required a minimum number of "cold degree days" in order to set fruit, and if we had a warm winter sometimes I wouldn't get any plums or peaches. The same might apply to quince... though I don't know.

I’d like to make an observation.

From September through November we had unusually warm weather here, with daytime temperatures sometimes close to 30 °C. What I noticed is that the trees not kept in shade started growing again.

One example: one of my Chinese quinces pushed multiple new whips directly from the trunk. These elongated 50+ cm in about a month, and they are still green or only just starting to lignify. Not surprisingly, these are also the trees that never shed their leaves or entered full dormancy.

In hindsight, my mistake was probably leaving them in direct sun during this period. Given the warmth and light, it makes sense that the trees simply kept growing as if nothing seasonal was happening.

Another observation: since most of my trees are grown on a balcony, I noticed a clear difference based on placement. The trees that were closer to the floor, where night temperatures are noticeably cooler, were the ones that entered dormancy first.

This leads me to think that soil/root temperature may be more important than ambient air temperature when autumn dormancy is triggered.

As an experiment next year, I plan to:

• Move trees that haven’t gone dormant by October out of direct sun
• Place them on the floor, in full shade, to encourage cooler root temperatures

I’m curious to see whether this will trigger dormancy earlier and more reliably.