Growing Daffodils, Soil Soil conditioners etc. & Summer Blooms. by Linda Wallpe, Ohio • February 10, 2010 • Comments Off on Soil conditioners etc. & Summer Blooms. Margaret – Long ago Tom Stettner turned me on to gypsum as a soil additive. Terrific stuff. It flocculates the clay, making it easier for things like leaf litter to incorporate. Linda W.