What sort of temperatures do you get in the fall. Nasturtiums germinate at 70 degrees. The plant will withstand frosts of a couple of degrees and will do well with temperatures in the 60's and 70's with the occasional higher temps. If you have those conditions then by all means plant them in the fall or when conditions are right. Be sure to soak the seed for 24 hours before planting and keep them watered so the seed can break free of that hard outer shell

Here is a calendar I found of our (94505 Blackhawk, CA) record and average temps by month. Start of September the highs are 87 but by end of November they are highs of 60.

http://www.wunderground.com/history/airport/KLVK/2015/9/14/MonthlyCalendar.html?req_city=Blackhawk&req_state=CA&req_statename=&reqdb.zip=94506&reqdb.magic=2&reqdb.wmo=99999

As for frost date, what site is the gold standard that people use?

This site says March 13/dec 13 for first/last frost probability of 50% - the station is very close to us though the elevation is much higher (on top of a mountain we back into somewhat)

http://m.almanac.com/content/frost-chart-united-states/CA/Blackhawk

But this site says may 12/November 12 - though all of the stations it lists are fairly far away

http://letsgrowveggies.com/california/94526/frost_dates/

Another site says March 7/jan 1.

My nasturtiums like rich compost soil which is exactly the opposite of what everyone has said. Plant in garbage sand soil. Well not mine. They also do not like a lot of sun. They function similar to snapdragons. They shine in Spring and Fall. I'm thinking of planting in Fall to see what happens. I need them to go to seed though. They don't like it at 90-104 degrees. It's too hot. They just shrivel up

I just pulled out a whithering petunia from one of my patio pots, and planted some nasturtium seeds. We have plenty of time here in Kansas before we would get a frost. I am looking forward to enjoying the beautiful flowers. I also suspect that the bunny that visits our yard will find their delicious leaves, too.

How Long Do They take from Seed to Flower?
Thanks