First, make sure you have slightly acidic to neutral pH soil; cannas do not tolerate alkaline soil. A soil test will indicate the pH of yours and you can read more about pH here: http://www.almanac.com/content/ph-preferences
Some sources suggest fertilizing only when planting; others suggest light fertilization with a 5-10-5 balanced product throughout the growing season (or perhaps halfway through; plants do not need fertilization as the season wanes). Put a spoonful or so into the hole when planting and consider adding fertilizer to the water and letting it dissolve before watering the plant later in season.
First, make sure you have slightly acidic to neutral pH soil; cannas do not tolerate alkaline soil. A soil test will indicate the pH of yours and you can read more about pH here: http://www.almanac.com/content/ph-preferences
Some sources suggest fertilizing only when planting; others suggest light fertilization with a 5-10-5 balanced product throughout the growing season (or perhaps halfway through; plants do not need fertilization as the season wanes). Put a spoonful or so into the hole when planting and consider adding fertilizer to the water and letting it dissolve before watering the plant later in season.