Not sure on the soil conditions, but the yarrow we have in our yard is very aggressive. Not sure if it would be a problem or not.

I agree with previous--yarrow is aggresive like mint, and will take over and probably push out any other plants. You didn't specify what type of Chamomile you are speaking of. Some are annual, though good at self seeding.

I ended up putting the yarrow in its own container, and the red clover and chamomile in the barrel. I believe the chamomile is Roman Chamomile, that's pretty much all I know. Thanks for your input!

Red clover is a short lived perennial. I'm not sure how well this will do in a container, but try it and let us know how it works. If you are looking to harvest flowers for use. you'll need a fair sized patch of it to get any real amount. I would suggest seeding a patch if that is what you intend.

Yarrow can spread but but it is very nice - even in your lawn. Read up on herbal lawns.

Chamomile is nice. I've had good luck with german chamomile (Matricaria recutita). Not such good luck with Roman chamomile (Chamaemelum nobile).

FataMorgana