Spinach, lettuce and swiss chard I plant directly into the garden boxes in seed form as they are fast growers and don't need the extra time. I will have to wait until the snow melts however and I can work the soil. Trying to start a garden here is always a challenge and as long as I win on occasion I'm happy. I regret to admit that our squirrels and chipmunks are all pretty fat though. We usually get about 10-20% of our raspberry patch and the critters including birds get the rest. What I'm really looking forward to is rhubarb pie and that is one plant we don't have to worry about as the critters don't seem to like it at all.
I read in Mother Earth News that seeds last for several years depending on the seed. Leaf vegetables like spinach and lettuce can last for up to 5 years. Carrots and radishes can be good for up to 3 years. I keep our seeds in a cool dry place and I have found that to be a pretty good estimate as to their usefulness. Looking forward to getting that garden in now that the weather is getting nice.