Tara took on the old cushions and brought them back to life and saved them.

She used carpet/Upholstery cleaner on the foam, let them soak for a while, rinsed, then vacuumed out the water.

About 3 times each.  One time used a mix of bleach and water.

Incredible amounts of sand and silt came out.  An interesting note, the dirt only gets about 1/2 inch into the foam.  We had a piece that was glued together and it came undone, so you could see a fresh side view.  The dirt is really only on the surface.
The green house gets VERY hot on a sunny day.  Great for drying things.