There are soil thermometers available from various sources but the calendar is really a good way to determine planting in your area. I would consider mid to late October a good starting date. I usually start some plants in transplant containers outdoors in the shade of a tree but where there is bright light, not deep shade. This is a cooler spot and allows you to get a head start. Keep the soil mix moist and then when plants have about 4 leaves transplant them into the garden.
Thanks for the question and good luck with you fall garden!
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