Each week after the market I have the issue of disposing of the seedlings that were not sold. This is because many vegetables have a vigorous growth habit and will be root bound by the next market or I have fresher stock ready for the next week.
For the last year I have been recycling these plants and soil through my deep litter chicken run (very happy chickens). Since I have started teaching vegetable gardening to the kids and teachers of my local primary school 2 days per week I have found a new way of disposing of them.
Other local schools that have a garden program can get a Monday morning visit from me. send me an email and I will schedule a visit to your school.