In northern climates, with about 120 days of frost-free weather,
annuals are traditionally planted on Memorial Day and can be
expected to do well through the summer months into September. Colder
temperatures in October favor a flower display rotation to more cold
tolerant plants like chrysanthemums and sedums.
Some favorite annual flowers include ageratum, coleus, Gerbera
daisies, New Guinea impatiens, nicotiana, snapdragons and verbena. Other than considering your garden soil and sunlight
exposure, careful thought should be given to the risk of deer
browsing and damage from other wild animals in your yard, such as rabbits. While
deer tend to leave some flowers alone, they will readily destroy
other flower plantings.
Also see our page: Popular Annual Flowers