Check pH, timer, nutrients and light

Steps to resolve

1. Make sure your pH is 5.5 to 6.5
2. Check your timer is set correctly for your environment, especially outdoors where temperatures shift
3. Confirm you have been giving the right nutrient dose, too little or too much can affect every plant at once
4. Check light, a plant may be crowded by a larger neighbor, or an outdoor stand may not be getting enough direct sun