Sweet potatoes? Not gonna work in a five gallon bucket. A much larger container - like a half barrel is OK. The vines grow like crazy so don't expect 'em to stay in any container.

If you're talking about 'Irish' potatoes, it's waaaaaay past the time to plant.

True true true. HOWEVER, this is an opportunity to figure things out. Take one bucket, fill it about 2/3 full of ordinary dirt, and then take one russet potato that's gone to sprout and perhaps is starting to dehydrate on you, and bury it just below the surface. Water and put in the coolest spot you can find.

Do this again in another bucket in another month.

Expect these plants to not do well, but eventually you'll hit on your timing with an investment of three buckets, no purchases of bagged "soil" from the store, and no loss of edible potatoes to use as seed. I thing your luck will start to improve when the weather breaks around mid September, but also think that everything you plant before that time will die a horrible screaming fiery death. Gardening is fun and interesting, no?

One potato a month...

PS: Potatoes in Summer and in pots (not buried in the cooler ground) is a double whammy.