I agree wholeheartedly that hardiness is important. It's not always easy to find out what's hardy before buying it, unfortunately, but I will definitely be looking at how well the cultivars I have/am getting will perform and see which ones appear to be weaker. Apart from disease symptoms, what would you suggest are good indicators? Obviously one way would be to compare cultivars under the same conditions (i.e. water, light, pH, etc.) and see which ones perform better (although "better" probably has caveats such as different cultivars having different heights, number of blooms, etc.).
