I would like to know weather i should soke the seeds first and then should i skatter then or plant.
This article should help. You do not need to soak the seeds before planting.
When do you cut back aster and mums in order to keep them shorter?
Their heights are set by genetics. Trimming them keeps them maintained, bushier, more compact, and healthier, but they will grow back to whatever height they were bred to be without root pruning maintenance. This would not be feasible in this situation.
With Chrysanthemums, the process isn't as straightforward. There are important timings that need to be taken into consideration:
Cutting back Aster is much more straightforward. They will tolerate it at just about any time. They will grow back to the original height if left alone, but constant pruning by 1/3 will maintain a set height.
However, pruning for maintenance after blooming is always a good idea.
I purchased it last fall. It's in a 1.5 gallon pot and was kept on my deck throughout the winter. I live in SE Wisconsin. I cut it back before winter leaving about 3 inches above the soil. Spring is now upon us and I see no signs of life. Is my aster dead? I don't want to toss it if it still has a chance.
New England aster is hardy to USDA zone 4 and your location is hardy to zone 5. If it was planted in the ground, it probably would have come back. But being in a pot all winter, its roots were only protected by a thin piece of plastic.
However, I would give it to June before tossing it. It could be late to break dormancy.
I have had a Blue Aster in my garden for 3 years, the first year it did have great flowers, but it never flowered again. The area that it's in, is great soil, and it receives afternoon sun!
That is odd. Are you cutting it back so it's not so tall? If so, that could inhibit blooming if it is cut beyond early summer. Cutting asters and mums back should be done by the end of June and no later. They benefit from pinching until then, too.
They do benefit from full sun. If it only gets west sun, that is just half a day. Here is more: