Pleurotus cornucopiae 608 was grown on a mixture of pasteurized cottonseed hulls (75% dry wt), 24% chopped wheat straw, and 1% ground limestone. The substrate was spawned at various levels (1.25%, 2.5%, 3.75%, or 5% wet wt) and not supplemented or supplemented with commercial delayed release nutrient (Campbell's S-41) at various levels (0%, 3%, 6%, 9%, or 12%). Maximum yield (weight of fresh mushrooms harvested at maturity) was obtained at 3.75–5% spawn level and 6% S-41 supplement. As supplement levels exceeded 6%, yields declined significantly. There was a negative correlation (r=–0.81) between spawn rate and days to production. As the spawn rate increased, the number of days to production decreased. By using a spawn rate of 3.75% of the wet substrate wt, it was possible to reduce the time to production by a mean of 9.2 days compared with a spawn rate of 1.25%.