As a result of the specialization in plug production, the large plug propagators sow the seed automatically unless a particular species has a seed type that does not work in automatic seeders.
After the plug sheets are filled with the proper pasteurized propagating medium, each chamber is seeded with one or two seeds. The use of two seeds per chamber ensures maximum and uniform production per sheet, but it does add some labor costs if thinning is later needed.
Germination of the seeds in the plug chambers can be done conventionally in the greenhouse benches under misting systems or in growth chambers if particular species require special humidity and/or temperature conditions. Whether in the bench or growth chamber, water application must be even and gentle to avoid washing out the seeds. Automated mist systems are preferable to hand-watering, even with fogger nozzles. Due to the shallowness of the plug sheets, there is always the danger of overwatering or underwatering. The sheets cannot become watersoaked; neither can they be permitted to dry out.