Mixing 5 and 9 week old chicks

[Nikichick123]

Is it a good idea to combine my 5 and 9 week old chicks?

 

[NatJ]

If you eventually want them to be one single flock, then it is probably easier to combine them sooner (like now) rather than later (when they are older).

How easy they are to combine will depend on the specific chicks and how they act.
It might be as simple as putting them together in one pen, then watching for a few minutes to see that they are fine.

Or you might need to put them where they can interact through wire mesh but not actually hurt each other for a few weeks (divided pen), then let them together under supervision, and provide lots of places for the younger ones to get away from the older ones.

As a general rule of thumb, the bigger the pen, the easier it is to combine chickens. Small spaces make everything much harder, because the chickens cannot get away from each other.