Some of the modern "environmentally conscious" packing peanuts are made from cornstarch and will dissolve in water. Either way, plastic or cornstarch, I would not recommend using those. The alternate ideas are all good; vermiculite, pine cones, empty plastic bottles, upended flower pots. Around here we pick up the beer cans from the roadside while walking the dogs and place them up-side-down in the larger plants, covered with landscape fabric.
