Already made the mistakes and made my own calendar for my location (all gardening is a local ‘fire and adjust’). Planted celery & celeriac in early July. End of July, sowed some cauliflower, broccoli, scallions, romanesco, kohlrabi, leeks and carrots all in cells. It is way too warm (for good germination) and too brutal (pest pressure) for these to succeed sown outside. Any direct sown seedlings are toast here in July->Sept. I use the AC vent to get close as possible to the best germination temps for brassicas. A discussion on winter growing was started here and continued for a few posts.
Early August, Cilantro, Rutabaga. Late August, Lettuce, Celtuce, Parsley, Basil, Spinach and white Turnip. Early Sept. Pak Choi, Sugar snap peas.
Most of this is growing under poly by mid November. I don’t have a heated greenhouse but the hoop house (high tunnel) works fine. I construct several low tunnels for the brassicas mainly- they need lots of room. When temps get down to the mid 20s I add row cover inside the poly of the hoop house (high tunnel) to capture ground heat and my celery and lettuces have survived down to 5 deg that way.
It is so rewarding pulling together a fresh salad in the middle of winter. 