Nasturtium Self-Sowing

Last year I grew nasturtium from seed in Reisterstown, Maryland, USA. I have read that they self sow, but I haven't seen any evidence of them starting yet. Should I give up and replace them with new seed now, or give them more time?

Nasturtiums, Tropaeolum majus and T. minus originated from Peru and the seeds may not survive severe winters. Also the seeds are huge and probably tempting fare for various rodents. Squirrels may not eat them, but I would not be surprised if they collect them and bury them somewhere as a winter cache. There are bound to be insects that love them too! I would get fresh seed just to be sure --and don't be surprised if you find seedlings coming up in the most unlikely places.