I really don’t think it is related to the depth. Roots less than one inch deep seem to survive just fine once established, even after a very cold winter. I think it’s more about the size and energy reserves in the roots.
They can get extremely invasive when they are happy. I have a hybrid I created several years ago growing in my backyard I named ‘Iridescence’. It’s a complex mix of Incense, Byron Beauty and wild maypop. It is smothering my kiwi vines and grape vines, and probably had 10,000 flower buds at it’s peak a few weeks ago. There a probably miles of roots out there. I would be happy to dig up root suckers next spring if anyone wants one. The fruits are not very large or numerous, but vastly better tasting than any maypop. It’s probably triploid, but does produce viable seeds and seedlings are typically fully fertile. Seems to be as hardy as wild maypops.
