Blooming anywhere from late summer to late fall, aster flowers range from 1 to 5 cm wide with many long thin petals. They have composite flower heads. This means that each flower is actually a group of smaller flowers consisting of ray flowers (petals) surrounding disk flowers (the centre). Disk flowers are usually yellow or burgundy, which make a nice contrast with the blue, purple, violet, or white ray flowers. An added attraction is their sometimes striking purple stems.