I would let it harden off in the shade and just watch it suffer until it adjusts to the new growing conditions. If it is well rooted it will pull through after looking bad for a day or two. Al

Oke, I will let it harden off outside.
I also had contact with another bonsai fanatic and he encountered the same problem, but only with his bigger boxwood cuttings. All of his youngher and smaller cuttings were doing just fine!
He grew them outside in the shade as you advised.

Does anyone have any self-experience with cleaning brances with 70% alcohol or diluted bleach + a tooth brush?

Thanks for replying,
I'll give an update on the progress.

Dennis

I have rooted box cuttings many times and I think that your problem is due to the plastic bag and the darkness. That will encourage weak floppy growth which is bound to be prey to fungal infections and unless brought into the light it is doomed to die. I simply place several small 10 - 20 cm cuttings into cuttings compost and put them outside in a sheltered area. I water once and then leave it to the rain.

I don't know why you placed the cutting in the dark. I've never seen that recommended.

I agree with leaving the bigger cutting outside and letting it take its chances. The temperature is not a problem.

also, I never use organic (or otherwise) potting soil for cuttings - it's sand, perlite, even vermiculite all the way for me - I even had some success using those expanded clay granules (hydroleca?).
IME, anything humusy or loamy, even sterile potting mixes, are really at risk of fungal contamination.
Yep, box is easy from cuttings.....but takes forever.

@florauk: I put my cutting in the dark shed because I thought that it was the best place for a stable temperature and no direct sunlight. I know now that it was a mistake.

The cutting is in the shade, no fungi, but also no growth for now.