PLEASE READ:

These are not grafted trees. These are seedlings, grown from seeds of the named cultivar. There are two uses for these plants.

First, you can grow them to mature trees. It is very likely that you will end up with a unique individual that has enormous seeds (all these varieties do) that is very similar to the mother tree. The orchards where these seeds are grown have all good varieties, so whatever crosses occur are probably very much worth trying out.

Second, you can use them as rootstock for scion of the cultivar with the same name. What? Well, chestnuts are well known to exhibit delayed onset graft failure. If you use a random seedling as a rootstock for your Dunstan (or any variety), you may get it to take and grow only to have the graft union fail at age 5, 10, or 15! What a bummer! The best chance for grafting is to graft a variety onto a seedling of itself. So if you have access to scion wood of Colossal, then you can graft that wood onto one of these Colossal seedlings.