|I live in zone 5 and various nurseries here sell Ilex Crenata|
|I would rely on specific advice from your local professionally trained nurseryman as to how best to overwinter this plant in your area and whether or not you have an appropriate site for it. Your zip code places you in zone 5A which is the coldest part of zone 5; in an exposed or windy site it could actually be as cold as zone 4. Knowing that, I would not recommend you plant these due to the winter hardiness question. You should also check directly with your nurseryman to see if they will guarantee them or not.
In general, the microclimate where these are planted is critical. They should receive protection from winter winds and be planted in a spot that is not overly wet, especially during the winter. I would suggest a protected spot with morning sun. Also, be sure to mulch the root area heavily in late fall after freezing weather has started. And, make sure the soil is evenly moist (not saturated or sopping wet but not dried out) any time it is not frozen. Do not fertilize or prune past midsummer as these steps would encourage late season growth that would not have time to sufficiently harden before winter. Finally, I would recommend planting them in spring rather than fall. This allows more time for them to become rooted and established before winter.