Sorry you are wasting your time. Seed potatoes are small actual potatoes that you save to plant the following year. Please do not consider growing potatoes from seed!

Thank you Moon growe,but how do you keep those small potatoes that you want to use as seed,from shriveling up looking unuseable ? when you buy seed potatoes they seem to be very firm and quite fresh.

Most often they have been stored in warehouses with carefully controlled temperature, humidity, and oxygen levels, then had the rotten or shrivelled ones removed before shipping. Bulbaholic tells me that growing seed potatoes is quite a skilled operation. Growing potatoes from the seed heads will give you quite a genetic variety, but only one out of a thousand is likely to make a good crop of usable potatoes. A few may even revert to the little raspberry shaped ones that the descendants of the Incas call "potato make young bride weep"--just imagine peeling the bumpy thing!! : D

Thank you for your replies. I had hoped to discover a cheaper way to get seed potatoes .It isn't though,just to save the money,it is the enjoyment of experimenting.

You can keep some of your own small potatoes back, at least from the main crop. Store them somewhere cool and dry and away from mice and the like. If you grow some of the heritage type potatoes you have to do this every year.