How much sun does the plant receive? In my location, soloman's seal can take quite a bit of sun. I think it does better with about 4 hours of sun a day. RW

Soil type might also be an issue. Otherwise, plant them with supporting plants, e.g. Hosta.

I have several large clumps of sol. seal and have never had a problem with them falling over or even leaning. My soil is usually fairly dry and I don't generally fertilize my plants. Maybe your soil is too good and rich for them. Mine are in mostly shade, so they don't need sun to stand upright.

Are these newly planted/transplanted? I had this trouble at first but as they matured, set down stronger root systems the problem fixed itself.

My solomon's seal is under a 100-year old maple. It gets no direct sun and the soil is very poor. I occasionally give them compost, and the plants are quite robust except that they flop. I put them there because I wanted the height and few other plants will even grow there. I was hoping to get some ideas on how to support them.