Petunias are flowering annuals that grow during summer season around the country. They bear bright, large blooms in pinks, purples, reds, oranges, yellows and combinations of these, and do well in almost any garden foundation. As draping plants, petunias thrive in hanging baskets, but must still get the right care for their growing calendar. If your petunia has yellowing or dying leaves, decide on your next step based on the calendar.
Treat your petunia based on the calendar. As annuals, these plants cannot survive frost, so yellowing or dying leaves may be a sign that temperatures are dropping and frost is near. If this is the case, move your hanging basket into the house, or a protected garage where temperatures stay around 15.6 degrees Celsius (60 degrees Fahrenheit). Maintain typical petunia care during the cold months.
Increase your summertime care to treat dead leaves in the heat of summer. Keep petunias in places where they get 5 to 6 hours of full sun every day, as the plants cannot live in shade.
Increase your watering to at least 5 cm (2 inches) of water every week. Although petunias are hardy to drought, brown leaves may be a sign of a thirsty plant.
Keep petunias in a mix of quick-draining potting soil and organic compost to ensure quick, efficient drainage and adequate nutrition. If petunias sit in tight soil that does not drain or restricts their roots, growth and health will suffer.
Feed petunias to give them resources for saving their foliage. Give the plants slow-release 8-8-8, 10-10-10 or 12-12-12 granular fertiliser at planting, then move to monthly feedings halfway through the summer. Always water the plants immediately after feeding, to help dissolve the fertiliser.