Not to hijack the thread, but I've had this exact experience collecting pinus rigida or pitch pines but instead of clay, they were growing in sand. When I collected as much of the roots as possible including a good amount of the fine feeder roots, the tree survived even when collected in summer. When I collected in winter and got little of the feeder roots, the tree did not make it. Both trees were about 1 inch in diameter at the base so I would guess 5 to 10 years old. I've had 100% success with the saplings and seedlings I've collected at any time of the year. I think the key there was to get all of the roots, just like you did
@19Mateo83 . Nice work!