Ipomoea nil can self resow in a zone 5 and the degree to which an I.nil will self resow is often very dependent on the exact cultivars,strains and how they may have (sometimes gradually) acclimated to a relatively cold wet environment...the same cultivar that has been grown out in a much warmer climate (e.g., Florida) for several or more generations may not be or retain cold hardiness,but will be better suited to the weather in whatever conditions is has been acclimated to...

I have known Hatsu Arashi to be one of the cultivars that has self resown in a zone 5,especially if there is a protective mulch layer in which the seed can remain 'suspended' above the usual conditions that would be present at the unprotected ground level.

The usual conditions at the ground level most often will cause the seeds to sit in wet conditions that repeatedly thaw and refreeze > which causes many seeds to take up water and burst when they refreeze...many tropical species have not developed the protective mechanism to hydrate only when it is late enough in the season to safely do so...but some species and cultivars can be progressively acclimated by intentional methods (usually through progressively selecting the most cold hardy plants) and sometimes 'accidentally'...

Hope that helps...

Ron

Thanks so much. I was sure I had these particular types re-seed after winter, as well as a few others. Usually, under the trellises appears a small group of seedlings from the previous year's vines. They are in areas that are mulched for winter. Some of the vines from these trellises produce offspring vines that do not bloom like the original vines.