Over fertilization of plants
If the outer margins of the leaves are burned, and you are seeing white crusting like salt buildup on plants and or soil that is a good possibility. Leaf curl too can be a sign. Just water the plants deeply to leach the salts away from the tender young root systems. Water more than you normally would to get the salts below the top 6 inches of soil. The plants should grow out of their problem if in fact it is excess fertilizer.