The economics of biogas production remain marginal, even on 'free' substrates such as wastes. However, new insights into the fundamental processes of solid-state digestion promise a much faster and more predictable process. This holds the future prospect of profitable biogas production from anaerobic composters fed with a range of solid substrates, including food industry wastes and biomass crops. A novel process model proposes that reaction occurs at a well-defined but mobile interface between raw and depleted wastes, forming the boundary of an independent expanding microreactor. Very small seed particles cannot establish such micro-reactors. The present paper explores the implications for seeding practice. Leachate recycle might do no more than compensate for erratic seeding, by transporting nutrients into well-seeded zones. Inoculating the waste with well-distributed seed particles of viable size could be more effective - and a great deal simpler and cheaper.