After a frost--Ty your germination rate is so poor. You probably got quite a few that were not ripe and the frost didn't help. Collect your seed before frost after the pods have turned brown. Let them dry for a few days inside, jar them and store in a cool dry place.

Do not sow them in a trench unless you want to do a lot of transplanting and any ditch will be burying them too deep. Broadcast them, rake in and water. Marigold seed has to be just covered with soil. Keep the area wet--but not too wet for a week and they should be up.