You can't buy any seed potatoes, unless you can find some old ones leftover somewhere. They might grow, if you can find them. The problem now is the summer heat and the summer deluges. You can always try, doesn't cost much, but grocery potatoes may just rot.

I pulled out my 'Red Gold' potatoes and planted some of the small and ugly potatoes in a grow bag, using the same soil. I'll see if they grow, but I have low expectations.

I imagine it is possible to order the proper seeds online but I don't have time for that.

I doubt grocery bought potatoes would rot.

I have 2 friends who only ever plant potatoes that way.

depends on where you are. As a kid in Virginia in the 40's we dug the spring potatoes around July 4, laid the small ones out in the sun untill they greened up. Then planted them for a fall crop. Dug in October when frost killed the vines.

I have also planted potatoes for a second crop in July. It worked fine for me though the spring crop was more plentiful.

Last year I planted shrivillled potatoes with green sprouts on August 1st. They were about my most productive crop ever. They were nice sized and hardly sprouted through winter and spring.