Controlling Japanese Stilt grass
Japanese stiltgrass is incredibly effective at outcompeting other types of vegetation. We do not have specific recommendations for native or non-native groundcovers that can prevent it. The key to its management is to try to prevent seed dispersal. Each Japanese stiltgrass plant can produce 1000 seeds and the seeds can remain viable in the soil for ~5 years. You can put in any type of groundcover that is suitable for your site conditions and then manages the area to remove the Japanese stiltgrass annually to reduce its population over time. If you already have a seed bank in your soil, this can take a couple of years of manually removing or mowing to prevent more seed dispersal. Recommendations for dealing with Japanese stiltgrass are provided in the following links:
My own experience suggests that Pachysandra is fairly effective in limiting the spread fo the grass. Also, it has been recommended to me that regular Mountain Mint and Appalachian ountain mint can be effective as well as Ragworrt. I found that regular Mountain mint was not too effective, but this might have been due to the poor quality of my soil. I have planted Appalachian mountain mint but I will not know until next year if it works. My ragwort was overrun by Japanese Stiltgrass, but I am going to plant more ragwort, but placing the plants very clost together to see if this makes a difference in fighting the grass.
Thank you for sharing your experience with what you have tried so far. Pachysandra (if it's the Japanese type) is itself an invasive plant that can get out of hand in woodland areas, so be careful about that. We no longer recommend planting it in landscapes located near natural areas. We would be interested to hear how the ragwort does for you with a closer planting. Please do share your results. So many people are dealing with Japanese stiltgrass -- it would be helpful to hear some successes in battling it so we can share what works.
Thank you Christa for your original answers to my questions and your suggestions regarding non-native Pachysandra. I have the non-native type, and it was planted about 1959 onto our wooded lot. It has spread over the years but not too much, and I am making sure it does not interfere with native plants. I would have liked to have used the native version, but my understanding is that it is not very effective against invasive species.