Thanks, Susan and Gordon!
Susan, I rinse them with a jet from the hose and dry them outside, upside down for two or three days, then store them in shredded straw for the winter. Each dahlia has its own labeled bag so if one rots they all won't rot.
For 20 years The Park was my husband's vegetable garden until the four heat waves in 2013, and the repeated (endless) attacks by the crows on the tomatoes. Then Jack gave it over to me so I redesigned the path, had it lifted and the head mason did a grand job. My intention is to mulch it well when I'm done with dahlia digging and some plant moving. Then, come spring, I can just watch as everything comes to life again. Planting the dahlias is so much easier than digging them in fall!
Yes, Gordon, this all was prime cattle grazing land back in the 17th and 18th century. Jack added enormous amounts of compost each year so the soil is rich.
Do you measure the soil temperature with a compost thermometer or just make an educated guess by the end of May? Sitting on the hot roof must be heavenly for them! I think we all have positive and negative aspects to our gardening. As long as we can continue to enjoy it I refuse to dwell on the negative.