How to Collect Marigold Seeds

The best quality seeds can only be collected in summer. Direct sunlight and the high temperature help the marigold flowers to grow healthy and fertilize appropriately. So if you want to collect marigold for seeds to sow next season, you should only pick the final blooms of your plants.How to Collect Morigolds seeds

I haven't planted marigolds for the last three years.  I leave the entire plant to over winter and then dig them in the next spring.  I live in zone 3a.  I have been transplanting the volunteers all over the garden.  The excess plants have gone to friends and neighbors.  They self seed everywhere.  I have large marigolds and small ones.  All sorts of colours. They seem to breed true to the parent plant.  They are a tropical plant so they aren't supposed to do that here.  You get more protection for you other plants by letting the marigolds overwinter.  You should try just digging the plants in and see what you get.  I used to start my seeds indoors but these are actually bigger faster than the ones I started in pots.  
I prefer to just let the marigolds just do their thing.  It is one less thing to start indoors, harden off, and transplant.  Most of them come up where I want them, so there is very little transplanting.  That leaves me time and space to baby other plants for the garden.

A few years ago I bought a few marigolds from the nursery, and planted seeds.  Although I had flowers from day one with the nursery plants, the seeds grew fairly quickly, and the difference between them was huge.  The nursery plants pretty much stayed the same. The seeds grew larger bushier, and produced a lot more flowers.
I live in zone 9 b, and I just let the flowers dry completely on the plant. The seeds just fall out of the bottom of the flowers. No extra drying time is needed.  I think marigolds are one of the easiest seeds to harvest.  Which is great because it is such a beneficial flower for the veggie garden.