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How to use this
Every crop has an ideal window measured backwards from your last frost date. Cool-season crops can be direct-sown outside before the last frost; warm-season crops must wait until after. Plants started indoors give you a 4-8 week head start, which is critical for warm-season crops in zones 5-7 where the frost-free season is only 130-160 days.
The dates below assume you have a heated indoor space at 65-75F. A seedling heat mat (78-82F at the soil) doubles germination rates for warm-season crops (pepper, tomato, eggplant, basil) per Cornell Cooperative Extension.
For light, modern T5 LED shop lights 2-4 inches above the seedlings beat "grow lights" at a fraction of the cost.