Answer: Basically, you can't. All you can do is go by the average last frost date for your area as a guide, and make a judgement based on the general weather trend each year. If you keep records of your own, you will also probably discover that your garden's microclimate tends to run ahead of or behind the official average. Your County Extension ( the Middlesex number is 745-3445) should be able to tell you the average last spring frost date for your area if you don't already know it.
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