Third, time your planting so the carrots will mature a couple of weeks before the first frost. My first frost is usually about September 20th. I plan to plant the storage carrot crop about June 20th. Last year it was actually planted June 26th. Fourth, Don't harvest until after the plants have received a killing frost.
Carrots are biennials.
The first year they build up energy in their root. The second year they flower and produce seeds. The frost is the signal to the plant that it is time to store energy for the winter. That is theory on my part but what is not theory is the fact that the carrots are sweeter after frost. Having followed those steps you will have an excellent product for fall eating.