Your seeds don't know what month it is

May first isn't magic. Neither is Mother's Day, or the last frost date, or the specific Saturday your grandmother always planted tomatoes. The seeds don't know about any of it.

What they know is soil temperature.

Germination happens when the soil is warm enough. Not when the calendar has rounded into spring, not when you've had three nice days in a row, not when the nursery starts putting flats outside. When the soil — a few inches down where the seeds are — hits the temperature that particular seed needs to wake up.

For warm-season crops — beans, squash, corn, melons, tomatoes — that's usually between sixty and sixty-five degrees. Some want it a little warmer. Below fifty, most of them will just sit there, slowly going wrong in the cold wet, doing nothing useful until you pull them out and replant.

This matters because air temperature and soil temperature are not the same thing. Soil warms slowly and lags well behind air. A week of fifty-degree nights after a stretch of warm days can fool you into thinking the ground is ready when it isn't. Conversely, a cool overcast week in late spring doesn't always mean the soil has dropped — it might still be holding heat from a warm stretch.

A soil thermometer is one of the cheapest useful tools you can own. Four inches down, seven a.m., before the day warms up. That's the real number. It takes thirty seconds and tells you more than the forecast does about whether now is the time.

Planted too early is not ahead of schedule. It's just early to sit in cold ground. The week or two you tried to gain usually doesn't show up in the harvest date. Early plants put in cold soil often get overtaken by later plants put in warm soil.

Cool-season crops play by different rules. Lettuces, peas, spinach, carrots — these want soil in the forty-to-fifty range. They can germinate near forty and will bolt once soil hits seventy. They have their own windows, and those windows close when warm-season plants are opening theirs.

Transplants are more forgiving than direct-sown seeds, but not immune. A tomato seedling you put out early will sit stunned until soil temps come up. You'll see it happen — neighbors who waited two weeks plant and their plants catch and overtake yours in a matter of days. It's demoralizing. The answer is waiting until the ground is ready.

Calendars are for planning. Soil thermometers are for planting.

Take it easy.