How and when does one stake them?

I have never learnt to stake flowers, because I just don't like to.

My planting are so healthy that I have to keep thinning them. I have the loveliest collection of choice irises all over the place. Just stunning.

Until they flop over.

I never seem to find the right time to stake them. Is there anything I can do so that I do not need to stake them? If not, when exactly am I supposed to stake them?

Is this a fertilizer issues? I've seen stunning irises at local gardens with not a stake in sight. Strong healthy stems. What's going here?