What do I mean by this?
Think back to last year, your Chrysanthemums were looking great about now, nice and thick, starting to gain some height, you thought to yourself, “this fall is going to look fantastic. But by August you starting to get a little worried, they were getting a little too tall; and by September they were bloomed out and falling over because of the flower weight, seemed like the stems were too long. This is why I say “Time to pinch and twist those Mums. And to do this is simple, just snap off the tips of each stem; grab the top set of leaves on each stem and pinch and twist them off.
In doing this you will stop each stem’s forward growth; it now has to rebuild the tip in order to start growing length again. Yet, in the time being, it has all this energy that typically went into “tip growth”. Where is it to go now? It goes into side growth production.
So now instead of just getting longer and spindly, it will stay a little shorter and get thicker. Instead of 20 stems getting two feet long you will have 40 to 60 stems staying a little shorter but with some meat on their bones.
Now when the flower bloom happens, which by the way will be a little further back into September; they should be able to stand up under the additional weight of a rain now and then.
I might add that one more pinching in mid July will make them even thicker and stronger, and push the bloom time back to around the end of September, first of October.