Answer: There are several possible reasons for why this could happen. One would be a lack of nutrients, so an occasional application of a water soluble fertilizer is a possible solution. You might try one that includes micronutrients in addition to the basic Nitrogen, Phosphorus and Potassium. Plants in need of repotting or otherwise stressed may also yellow and look poorly. Excessive heat can cause yellowing, as can overwatering. In any case, try to get the hardened off and in the ground as soon as possible and do move them to larger pots if they are becoming rootbound.
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