Answer: I apologize for the delay in answering your question. This kind of question is perplexing, because there are many possible answers. Some cultivars simply bloom more reliably through more varied conditions than others. Sometimes individual plants may become better established than others, with the weaker plants blooming less. Sometimes they may have been treated differently prior to purchase, with the possibility being that early stress can sometimes have long term effects on performance. Also, some growers will fertilize differently than others so you may have some that received a slow release feeding prior to purchase while others did not. The vigor of the parent plant, if these are cutting grown, can affect performance and seedling variation if these are seed grown can affect performance. Sometimes if you re-use potting mix from one year to the next or use different bags of mix there can be variations in the structure, water or air holding capacity or fertility that are reflected in blooming. Sometimes too although all locations seem the same there are differences such as wind exposure or a roof overhang that can affect conditions and thus performance. These are the types of reasons I would suspect and consider, I hope this helps you trouble shoot.
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