Q.can a california poppy grow in zone 5b?
What is the best poppy to grow in zone 5b? Will a California poppy grow well in 5b zone?

It is possible that they will grow, but they may not last long. Any of the true poppies (california poppies are misnamed, as they aren't true poppies) would be more suited for this area. There are many varieties to choose from, and I think you will find something suitable to your liking. This article will help: https://www.gardeningknowhow.com/ornamental/flowers/poppy/growing-poppy-flowers.htm

California poppies aren't hardy in 5b but they set so much seed that new plants come back the next spring. Treat Flanders, aka Shirley poppy, Icelandic and breadseed or opium poppy as annuals that self-sow. Collect seed to be on the safe side.There are other poppies that are perennial in your zone. These are the oriental poppies with many colors and textures available. Poppies need full sun and well draining soil. Most poppy species go dormant in summer, California poppies being the exception. Here is a link to articles on growing the different types of poppy. https://www.gardeningknowhow.com/search?q=poppies%20flowers%20how%20to%20grow