I've grown cosmos this year, sowed in a seed tray and put on a windowsill. Just covered with a propagator lid to keep moisture/warmth in until they germinated. No need for heat lamp with these, don't know about the other seeds you mention though.
I sowed 15 french marigolds in a seed tray at the end of Feb and put them on the back porch windowsill. No extra light or heat. 14 germinated. Not sure what went wrong with the 15th one
I sowed mine beginning of march, north facing conservatory, they are about 8 inches tall, half seed trays for everything, find this is a good size,they stay there till I start hardening off next month.
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