GardenWeb.com is pretty good, LOTS of topics. The advertising is very annoying, as it's now owned by iVillage. But it's a popular site with many knowledgeable people. Once you sign up, you can ask questions and have the answers sent to you as email, as well as on the thread.
It is probably one of the best sites for Winter Sowing, and is referenced by Trudi Davidoff's Winter Sowing website at
http://www.wintersown.org/wseo1/How_to_Winter_Sow.html Trudi is a genius (I think). She first came up with the idea several years ago on the GW site about sowing seeds outdoors in fall and winter, saying that she had been experimenting with some seed species and varieties, basing her idea on two basic premises: many plants will naturally reseed, no matter what environment, and she had noticed that many species/varieties had 'cold' names, like 'Siberian', "Canadian', etc.
I've been doing it for four years or so, and it works great, esp for the ones that need winter chilling and you don't have space in your refrigerator.
I have a thread here that gives the bare bones, under the Permaculture section:
https://permies.com/permaculture-forums/955_0/permaculture/winter-sowing ATTRA has a large, informative site on sustainable gardening and farming at
http://www.attra.org/ (It used to be called Appropriate Technology Transfer for Rural Areas, but they changed the name to National Sustainable Agriculture Information Service, but still kept the acronym ATTRA, probably because it was easier to say than NSAIS (and too similar to the stupid and dreaded NAIS).
Sue