my spinach seedlings which i started indoors about a month ago and are still tiny, were just transplanted outside seem to already have a little flower in the center. how is that possible?
Spinach is better sown outside, in cool conditions. It might have been too warm inside for them.
Spinach not only likes cool temps, but short day-lengths. The days are getting longer now, and that's their signal to set seed.
Try sowing some in Sept or Oct, when the days are shorter and getting more so. Next year, start as early as you can, like Jan or Feb.
Also look for bolt-resistant varieties. I grow Space hybrid, which seems to last longer than most others I have grown. I have also overwintered fall plantings of Space hybrid, and have had them last longer than spring planted spinach of other varieties.
also old seeds tend to bolt