Other than not flowering, what is their general condition?

Yes they are very healthy. I have white and rose. The plants differ in their colors. The rose colored ones are
smaller and darker leaves. The white colored ones are a bigger plant with light green leaves.

Are you perhaps located in a coastal location that doesn't get much summer heat? They can be shy bloomers if it never gets hot enough to encourage blooming. Around here in Berkeley, they only bloom well with reflected heat or no direct coastal winds, while just over the hills in places like Walnut Creek, they are just covered with flowers already.

If heat and enough water to encourage good growth is not the issue, try fertilizing them more regularly.