If your hanging basket or window box has dried out or becomes difficult to water, it will require swift remedial action to attempt to save the plants.

Soak the basket in a basin of  SLIGHTLY suddy water, using ordinary (NOT ANTIBACTERIAL OR SCENTED) washing up liquid for 12 hours.
After the 12 hour period pour the left-over water onto the basket and rehang the basket.
Continue to water every day.