I have received many questions about tomato leaves curling. The most common reason for this during this time of the year is environmental. It even has its own name: physiological leaf roll. The plant is growing rapidly and the roots are not keeping up with the top, the leaves’ natural response is to curl to reduce its transpiration. This common when it is excessively hot or windy. The good news is the plants will gradually outgrow this.
To help the roots out, try a layer of organic mulch like straw or rotting alfalfa hay. This keeps the roots cooler allowing for quicker growth preventing drying out especially if they were root-bound before planting.
A quick note: tomatoes and peppers like a smaller dose of fertilizer than a high dose.
