I find that the first year after planting, they are fuller, and thus the weight makes them topple. I use short metal stem stakes that have an open loop on the end. These are about 16 inches long: too long, but useable. Avoiding the bulb, I push them deeply in, then hook the stem into the loop.

In subsequent years, the florets are not as dense, then they don't flop.

Thanks Linnea, I do wonder why that is though. Are the bulb producers doing something that makes them fuller? I wonder if there are any efforts to breed a stronger stem into newer varieties. I am surprised at how erect the 'City of Haarlem' is in comparison to every other variety in the garden, and it is in it's first year.