Answer: You are probably overwatering. Plant roots need oxygen to thrive and if soil is constantly wet, they will rot. Apply water to the soil (not sprinkling foliage) slowly and deeply. It should penetrate to a depth of one foot for mature annual flowers. Put 2-3 inches of mulch on top of the soil to retain moisture. Water when the top inch of soil dries out. You should not have to water twice a day. Also, shallow, light watering allows salts to accumulate in the top layers of the soil/root zone, which will kill the plant. Also, snapdragons are susceptible to a variety of fungal conditions. If you plant them again, rotate the planting site so fungal diseases have less opportunity to build up in the soil. As for it being too hot, I live in Arizona where it is much hotter than 75 and snapdragons will grow! Finally, snapdragons are annuals; it may be that your plants reached the end of their life cycle.
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