There's a couple of ways you can do this :-) Do you grow dahlias? If so, just harvest and store the tubers the same way you would a dahlia tuber.......wait until a light frost knocks back the foliage, dig up the tuber and rinse off the soil, allow to dry slightly and wrap in newspaper and store in a cool, dry location for the winter (like your basement?). Or, if you grow in a container, just bring the container into frost-free storage for the winter. No water.

Thank you gardengal. Yes I do grow dahlias so will store it like I do them. I just wasn't sure when to dig it - so will wait for a light frost.

gg, really? all these years i've been thinking cosmos was an annual grown from seed.i had no idea it had a tuber. can one do the same dahlia treatment with the ipomeia(sp)?
best,
mindy