I recently purchased a Solomon's Seal and have just repotted it. I noticed that after repotting, all the flowers have withered and hardened. What did I do wrong?
You probably did nothing wrong. Plants simply do not like to have their roots disturbed which is unavoidable with repotting. On the other hand, Solomon's seal blooms for a brief period and then, if pollinated, forms berries. A developing berry may be what you describe as "hard". Solomon's seal need shade or dappled light coming through overhead trees. It will slowly enlarge to form a nice clump, sending up more stems each year.