Best planted after the soil is thoroughly warm in the spring, about 70*F. They like a lot of water, rich soil and usually make tremendously long vines, unless you have a "bush-type" but 'field' pumpkins are usually long-vine. Lay foil on the ground around the stem after they are a couple inches tall, to help discourage borers.

Mine were planted 3 weeks ago and are doing fine. I am in Fresno. One night was cold while they were still in small planters, before I transplanted them. It didn't bother them. These are from a seed packet. I think they just need a long season to get their full size. If you plant them from now to May they should do great. Of course, all my experience is with the packets from stores.
What is a Field pumpkin? Are they the pumpkins the commercial growers use or are they wild plants, if there is such a thing?
I would be interested in finding out how they do, if you would have the time to send the results in the Fall. L.

We have a pumpkin patch, we are in zone 7, If we want the pumpkins to be ripe by the first of October, we plant on July 4th. We plant several different varieties, it takes about 85 days for ours to mature. I hope this helps.