Winter care for Imported Pinus Parv. in Zone 7.

I bought a White Pine, grafted in Black Pine root stock, from a nursery in Shanghai, China this Spring. The tree is 40 years old and is growing very well. It is budded up for Spring. I Winter my trees on the ground, in mulch which covers the pots. They are up against the sides of the garage, three deep at most and have some wind protection. I read about Winters in Shanghai and am wondering if my "way" to Winter this tree is sufficient. Or should I build a cold frame or something? I am in Zone 7. I believe Shanghai is Zone 7-8, depending upon the micro climate... Does anyone have suggestions or thoughts about this?
Thank you for your help. Todd

You can just leave the tree outside. Or you can mulch it in the ground just in case but I really don't think it is necessay. In zone 7 I don't think you need much protection for the outdoors.

Robert

I mulched the tree on the ground last winter behind my garage and it did fine and grew strong this year. Thank you for your help.
Best,
Todd

This does bring up an interesting point. Black pines are the coastal pines of Japan. Five needle pines are the higher mountain pines. Grafting it onto black pine stock probably gives it a lot of strength, but those roots probably can't take as much cold as regular five needle pine roots and that might be a problem farther north.

But like Robert said, you're fine either way.