You can cut them back as far as you want and they'll regenerate. I usually let the first flush set seed then drop the seed pods when cutting back (do the same in the fall) to ensure an unending supply of new plants. Don't know why I do that since I always get a million of them every year anyway.

Such a nice plant. I pretty much do the same thing with forget-me-nots. Those are about done now and setting seed - I scatter those seeds too when I pull the old plants. Again I'm not sure why since they, too, are prolific self-seeders.

I just rip them out when they get old and ratty and dead looking. They set seed and give me plants again when it's cooler out. I like cleaning up the spent annuals and having nice clean spaces for new plants. If I just cut them back, I have to look at ugly plants for a month or 2 till they grow new leaves.

i would say... for what its worth.. that it depends on how much seed it already produced ...

annauls have one goal in life ... and once accomplished.. they die ...

and that goal is reproduction.. aka producing seed ...

if deadheaded properly ... removing the seeds ... you can keep an annual going for a very long time ...

but if your plants are already in decline .. because teh job is done ... cutting them back hard.. may of may NOT work ...

sometimes.. they are just too far gone ... and once you cut them back.. they never look right again ...

but since they are already tending ugly.. what do you have to lose ...

since you provide no pic .... its hard to speculate.. whether it will work for you .... but you have no choice ... but to try to remeber next year.. to do it a bit earlier ....

look to leave a viable bud when you cut on them .... that increases your odds ...

ken