To have butterflies in your garden all season, you need to provide a variety of nectar bearing  plants so you will always have an available food source for them.  These same flowers are often used by hummingbirds & other nectar loving critters such as bumblebees, sphinx moths, honeybees, tiny wasps & myriads of other critters. 
 

Remember the most important thing: IF YOU WANT BUTTERFLIES AND OTHER NECTAR-LOVING CRITTERS IN YOUR GARDEN ALL SEASON, YOU MUST HAVE  NECTAR SOURCES  ALL SEASON! Click for larger view

Our listings of nectar-bearing plants indicate their bloom season: early/mid/late, or a combination. 

It is very difficult to know what month plants will bloom in other zones.  Here we are in zone 7 and we have an extended gardening period so I've tried to give you an idea by the time of season to expect bloom.  If you plant something in the spring, and it blooms that year, that is not necessarily the normal time of blooming.  The second year it blooms should be correct.