Do the plants pick up after watering ? I only ask as overwatering and underwatering look the same and if your sure that the soil is drying out and that your not overwatering It could be underwatering. Heat can dry out soil quick. You could try a cover for your pots. I cut circles out of cardboard and wrapped them with Mylar sheeting, put a slot in card for plant stem and hey presto a cover for your pots that will help to stop the soil drying out so quick, plus these have the added bonus of reflecting light back up from under the canopy.