September is the first month of fall and is typically when most flowers have lost their blooms. If you want flowers to continue in your lawn, then you will need add plants that bloom in the fall months. There are several from which to choose that will provide a lot of different shades from more traditional fall colors to bright spring colors like pinks and purples.
Marigolds are another popular fall flower. They give off a strong odor to prevent bug infestation which is a benefit to all plants you grow near to them. Blooms start in late summer and September. Colors vary a bit, but most found in stores are yellow and orange. They don't need a constant tending, but to encourage new blooms, pinch off dead ones.
Zinnias are a beautiful fall colored flowers that is easy to care for. There are several different varieties of the flowers ranging in height from about 10 inches to more than 36 inches. The blooms differ in styles with some having a single row while others have multiple rows and are more cone shaped. They should be grown in rich well draining soil with lots of light. Blooms show up in late summer and last through September and October.
Sunflowers can be grown through the fall season and vary in size. These flowers have large blooms and prefer to be planted in rich damp soil. Locate them in full sun as their name implies and give them an overall fertilizer to encourage healthy growth. Water to keep the soil damp when they are first planted. Once grown they can last longer without water due to their root spread.