Casuarina Equisetifolia - Is my bonsai dying? Need Help

[Baia]

Hey everyone,

I'm new to the bonsai world and proud about the recent development of my Casuarina Equisetifolia seedlings.
I've started with some seeds in April and they've grown pretty good. But some trunks of my casuarina's changed their colour into purple. Not brown or yellow. Kind of a mix between brown and purple. My guess is that they had too much sun through the whole day with maybe too less water...But I'm not sure.
I place them on the outside on the sill, to get the most out of the sun and the heat. The soil is a universal bonsai mix.

• What else could it be?

• And how should I react to this?

• Maybe by placing them inside and not in direct sunlight?

I also pruned some branches, because they were too long compared to the main trunk.

• Is it maybe too early for pruning at this bonsai age stage?

Hopefully you can help me with some tips.
I'm happy for any response.

Best wishes from Germany,
Baia

[shibui]

I think this color change is just the natural progression from young green stem to mature wood. It should keep changing to brown eventually.
We don not keep casuarina inside but I don't think they would like that much. Outside is best. I don't think they can have too much sun either but moving from inside to full sun could give some sunburn.
You can prune any time but any pruning will reduce growth rates. It will all depend how long you want to wait for your bonsai and what you want it to look like. Personally I do not do any pruning until the trunk has thickened. I know I can prune casuarina even when they are big and thick and still expect to get lots of new shoots to use for new branches.