Is it too late to plant potatoes?
In Tennessee ? Probably.
I'm close to Charlotte NC. March 1st is my target date for potatoes, lettuce and radishes. They can handle temps down to freezing, but potatoes suffer in dry, hot conditions, while lettuce and radishes 'bolt', meaning they turn bitter, a large center stalk rises up out of the plant and goes to seed.
Temps of 85°F are too much for those crops.
Potatoes can grow in the fall. Check your first frost date in Oct/ Nov, and back up twelve weeks. Dug a six inch deep trench, loosen the soil in the bottom of the trench add Shake and Feed (or some other slow release fertilizer) and set your seed potatoes about a foot apart.
You cannot fertilize them once they are in the ground (hence Shake and Feed). But you will need to water regularly (rain is best). When the plants (actually vines) get close to a foot tall, "hill up" with additional soil to support the vines. And keep watering.
When the vines are DEAD, get a shovel or a garden fork and dig out the tubers. Come in from the sides of you hills, and be careful not to harm the yield.