Here is what I am thinking:
Zone 6 is a little better but I still think you will have a hard time keeping them alive. Worth trying regardless.
1. Stratification is not needed. The seeds are cheap enough. For $40 I got one ounce, which is approximately 6,000 seeds. Even if you do a batch of 100 seeds at a time, you will end up with enough germinations that will keep you occupied for the whole season. I did 400 at one time and ended up with 150 germinations. What you do not appreciate at the beginning of the journey is how much time is required to take proper care of just 20-30 seedlings. 100 unstratified seeds should give you between 10 and 40 germinations. I germinate on a coffee filter with regular tap water. I normally spray it with Dakonil, which kills any potential fungi. Typically you get first germinations after 10-15 days and then they keep popping up for about a month.
2. I use pure peat moss with about 1/5th of perlite by volume as starter medium. Make sure to mix it with water so that it's very damp like a wet sponge. Seeds do not require any sun to germinate but after they have germinated the more light the better. I use fluorescent lamps, both 2 ft and 4ft version with 6 lamps in each. Try to keep the light about 6-8 inches from the tops as it really helps with the growth. My last couple of batches I kept lamps about 12 inches away and they still did okay. With 12 inches away it's much easier to water without moving the lights. If you decide to keep lights close be careful not to overheat. I used to have a small fan blowing atop the seedlings removing any potential hot air build up. Water once a week. I have a measuring flask, each seedling would get about 50ml. That seems about right for a week for my humidity and temperatures. Do not worry too much about exact water amount. As long as the containers dont get too light, they should be okay. I read that too much water may cause negative effects but in practice did not notice that when I over watered. I do use fungicide. It is in my experience #1 remedy for healthy young seedlings. Aforementioned Dakonil (chlorotholanil active compound) is the miracle drug for sequoias. I lost countless hundreds of sequoias before I started applying Dakonil. They do not need it often but once about every 6-8 weeks a spray of Dakonil keeps troubles away. I do not use any fertilizer, although I did an experiment with an unlikely "fertilizer" - magnesium sulfate, about 2% solution - with seemingly great results. It's hard to say if that was really the effect of that magnesium salt or just LOOKED better to me. The reason why I decided to add magnesium was because since I used just peat moss I was thinking that would really have practically no nutrients. Where would Mg2+ would come from to form the chlorophyl for the green needles? Obviously some is available in tap water, but I thought jump starting it with an extra shot of Mg2+ would not hurt. And it did not. I apply that solution every 4-6 weeks instead of watering with tap water.
3. I do not think there is any limit on how long you would want to keep them inside during winter. Eventually you will have no choice. They grow. They really really like sun (with plenty of watering) during summer, but if you have space indoors to keep them then by all means, do it. By year 3 some of my sequoias got to 3-4 feet tall and 2-3 feet wide. It's okay to keep a few of them inside but it becomes impractical for anything more than 10 unless you have some large indoor space for some reason. I no longer think that keeping them inside is bad for long term survivability. However, once they go outside, you would have to protect them till they get firmly established. This means, I am guessing now 5-7 years outdoors. Developing root system is the most critical part of the process. If you have means of planting 2-3 year sequoias outside and keep them protected over next 5-7 winters then I think that is the most real chance to establish them.
4. No, I do not regularly water them when planted outside. All trees that got planted outside never showed signs of being water stressed. The two nightmares are fungi and winter desiccation. When it is really hot and dry then yes, I do put some water around them, just in case, but as I said, I never observed water related problems. One time I had moved a very large seedling (4 feet tall) from a container into the ground. Because it was so large and heavy (mostly because I did not want to damage the root ball with a lot of soil) that it took me several hours of moving stuff around. The top of the tree drooped severely and most branches drooped as well. After I placed the tree in the ground I watered it thoroughly and by the next morning it was back to its normal self. Never had that problem again with that tree (till it died from a severe fungus attack).
Other tips - spray early in the spring with Dakonil. Then repeat in the middle of summer and again in the early fall. Fungus starts to develop and then quickly takes over trees in late August-September.
Now more of a speculation, since I have not really attempted that yet, it will be required to protect them for many years from the winter cold before the roots develop wide and deep enough to pump enough water. I have now build a large foam cone, stealing the idea from the so called "rose protectors". Stealing, in the sense that I just re-used the idea of an octagonal pyramid made out of styrofoam, only larger. I built an experimental 8 foot tall protecting cone for the next winter, will see how the sequoias fare under that. If the cone itself survives that is. We have severe winds here in Iowa during winter that may exceed 50 MPH. And they can be blowing for days with temperatures deep into the negatives. Longer term solution for me is that I am now growing several barrier walls of hardy conifers around the future sequoia site with the idea of breaking up the severe winter winds. Even with that, I think I will need to keep wrapping large sequoias into some protective layers for years to come.
Good luck and share your pictures.
