I agree with Carrie. I have planted small plugs up through Thanksgiving and we are on the border of Zone 3 and 4 here in NE Iowa. The root system is the most important part of the plant any time that you transplant. The fall can be deceiving and people who purchase plants this time of the year are sometimes disappointed that the tops are shaggy or sometimes non-existent. Don't get discouraged. Take time to observe the root system. Select plants that have healthy roots. If the root system is dark and slimy, it is not a good plant and might even be dead. Choose plants or plugs with turgid, proper color and are not root bound. Don't forget...plants have different colors of roots so become familiar with the colors. Also the density of the root system varies with different plants. For instance: Prairie Dropseed has a fine reddish colored root system while Cardinal flower has a very white root system that is very dense. Don't compare one species to the other. Only compare same species with each other when checking the root system. So purchase your plants now and get the jump on next year as your plants will spring forth and be way ahead of those later plantings in the spring or summer.