Answer: Yellow leaves can be caused by many things including lack of nitrogen, insufficient light, water-logged soil (plant roots need oxygen to thrive), dry soil, or iron deficiency. If the older bottom leaves are yellow, but new growth is green, it's usually a lack of nitrogen. If new leaves are yellow, with green veins, it's usually a lack of iron. (Lack of nitrogen is a more common problem than lack of iron.) Soil should be kept moderately moist (but not wet). Since you have had so much rain, it could be a combination of overly wet soil and the rain leaching the nutrients out of the container. You didn't mention if you fertilized, but I'd suggest using an all-purpose fertilizer that has a higher middle number, such as Miracle-Gro (15-30-15). The middle number is phosphorus, which promotes bloom.
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