They don't have to have boggy conditions. Will grow well in ordinary enriched garden soil with regular watering. For a container, sub a good quality potting soil for the garden soil.

Try instead installing something like a sheet of plastic in the soil some distance beneath where the primrose is then planted in order to create an artificial barrier to soil drainage. If you use a big enough sheet you can develop a grouping of multiple primroses, and/or an entire bog garden planting featuring a variety of subjects.

Thank you all for great ideas. Such pretty plants but rather hard to find in U.S. Thinking maybe they fail because folks don't realize they need lots of moisture.....

Most primroses need a cool summer climate.

They don't need any more moisture than Siberian irises do. They can grow perfectly well in regular garden soil with regular irrigation. But they do prefer shade and are not very tolerant of summer heat and humidity.

When you say container, are you thinking a pot or something without drainage holes? Something without holes might be a decent option, otherwise like others have mentioned, a plastic liner should work well. Just take it easy with the drainage holes, you can always put more in later if there's a problem.

Mine do well here in Pa in a spot where water from the neighbor's yard seeps through.

Have you considered Primula sieboldii? It might be an easier choice than japonica. Both are easy from seed if you're having trouble finding them.

Thanks katbob. Do you winter sow your seeds or start them indoors?

I think you could call it wintersowing. A small pot filled with soil, sprinkle a layer of chicken grit on top, sprinkle the seed on top of that, and just put it outside. Do that anytime during the winter and the seedlings should come up in the spring when the weather warms.

I don't know how serious you want to get, but the American Primula society opens up their seed exchange around March I think? to nonmembers, and for a few dollars you can get some of the best seed available.