same problem here!
Mine are in large pots and the branches are drooping by the sides, with many broken off as well. I am going to put these into the ground next spring and will leave them as is for now.

Unfortunately it's too late for this year but the key with mums is pinching. To keep them from getting floppy, you have to pinch them regularly til about the Fourth of July--it all depends on your zone. Otherwise they get leggy and flop. Don't forget...there's always next year.

Or you could use a metal grid ring! Im going to try using one on my annabelle hydrangea, which insists on flopping all over the place. Pinching of course too!

I guess I'm not pinching down far enough. I'll go shorter next year. I guess it's live and learn huh?

Those mums that are planted in the ground will develop roots where the stems flop on the ground. Flopping is a natural occurance for them and promotes new growth. Luckily the roots of mums tend to be quite shallow so if you don't want the clump to get larger you can just pull out the floppers and move or compost them. Cheryl

I learned too late that a single early June pruning wasn't enough. Next year I'll be pruning as late as early August.

That's right. You have to pinch regularly--not just once. But if you pinch too late, you will cut back on the bloom. Of course, you are in LA and I am in MA--two different gardening worlds--so the cut-off date will be quite different.

For my zone, I've always heard pinch until july 4th. However, I don't pinch or prune mine except to deadhead occasionally, and my mums are fine, I have one in a pot that is years old, it is blooming fine now. I have several in the garden, also years old, they were in pots originally and then put in the garden. All are in bloom and are fine. Now maybe if I'd pinched them they would be fuller but they are showy enough for me. Go figure. And they are not flopping. But if they were, I would use one of those rings I think they are called a peony ring.

I'm growing Country Girls. With only a single pruning they bloomed beautifully this their first year, but they're way too lanky. I can only imagine how much stronger and fuller they'll be in future years with proper pruning.