Zone four is too cold for Japanese Maples. Your best option is probably to grow it in a pot and then bring it into a protected environment (like a garage or basement) during the winter months. Japanese Maple roots are killed at 14 degrees F.

So I would pot it up in a nice pot with good potting soil and good drainage, water it well, and SLOWLY allow it to be exposed to colder temperatures. Eventually you can let the pot freeze completely, as long as its not exposed to extremely cold temps. Later in April, you can bring it out of "cold storage" and it should do just fine. Then next winter bring it in again to protect it from the extremes of your climate.

I know a grower in up-state New York who puts all her JMs in a cold storage warehouse for the winter. The pots freeze solid, but they're protected from harsh weather and extreme temps. In the spring she lets them thaw out and they do beautifully after that.

Regards,

K4

If it's not in leaf, you can put it in a refrigerator or cooler (depending on size) and keep it long enough so you can plant it directly outdoors when temperatures allow.

Al