Root rot after winter period

Hi everyone!
After the winter period I lost some trees due to root rot.
During winter I protect my trees in a plastic winter tunnel but the soil of the tree stays wet.
From October to March I don’t get sunshine in my courtyard .
When spring starts the needles starts yellowing and during summer my tree died. I tried to repot in new soil but it didn’t help.
Does someone had those same problems before?
How can I solve this?

How much air movement was there in the tunnel?
I imagine there wasn’t much being in a courtyard.
A box fan on the lowest setting will provide good air circulation.
How much watering?
Without seeing your situation, I’m not sure what watering would be. That would be for you to set.
I think that good air circulation and less water with no sun would help.

I putted a small fan into last year because a thought that the air circulation would help.

Tomorrow i will put a picture . Thank you for the reply.

could be related to your potting medium, what you are using, and how old it might be, time since last repot, etc.

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Jusf my survival strategy… (Pacific NW)
The minimum winter temp should be<30 F for most of the 3-4 months to justify a poly tunnel, or overed storage in the dark for my bonsai. I prefer they be covered with SOME snow before covering. Keeps the roots cold enough so mold doesnt grow.
If the ambient temps get above 45F, the tarp comes off .
I have had root ROT problems 3 times recently (Not a winter thing…). The trees survived because I watch and listen to them… I see that others usually dont notice it untill the tree is already dead…
The last few winters have been hard here on bonsai… the temps go from Nov at 50F to 20, then back to 50 for a month. Feb goes to 10 and then back to 45 and back to 20. The trees have problems telling when it is spring, too soon…and then freeze again. If I don’t stay on top of it, the trees suffer… fungal and bacteria tree deaths…
Oh, BTW, the GOOD natural bacteria & fungi in the bonsai soil is a GOOD thing. Protects the soil from BAD stuff. Just like in your gut.
Some fungal myccelium threads will grow up into the mulch. Just brush it off with the mulch. I have seen white truffles in my oak forests… endosymbionts for mutual benifits…
Basics. Balance of water & oxygen…

I had the same problem last year. I stored my trees in the basement, all time above freezingpoint. As i realized that some of my trees are dead, i inspected the roots and all of them had been muddy and damaged. A long raining-period in fall, way to much water in the wintertime and bad soil was the worst combinatin for my trees (i overwatered them). The reason for overwatering was very pour soil (unfortunately i have seen the soil-stream seen to late, the rest of trees had to stay in that soil the complete growing season). For this winter, i started to change the soil and take much more care on watering and i am sure, the problem will not occur again.


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Bonsai soil is 1:1:1 akadama, lava,pumice.
Here in Belgium our fall and winter has a lot of rain . Last 2 weeks it was raining all day during those weeks so I put up my tunnel to protect them from the rain. So my courtyard is very humid during the winter .
During exstreme freezing days I put the bonsai pot in styrofoam box and cover the pot with bark.

Here in Belgium we had also the same problems in late winter /early spring. Some days get 12°C and frost during the nights…
Thanks for the reply.