August 10, 2026 · Updated September 12, 2026

What winter garden seeds you can sow depends on your yard

Whether a winter sowing lives depends on the coldest night your particular yard reaches. A seed packet gives you a regional average for a whole zone. Your yard can run several degrees off that average, and that gap decides what sprouts and what rots in the cold.

How cold decides what germinates

Seeds germinate on soil temperature. The ground they sit in sets the timing. Cold-hardy crops like spinach, lettuce, radish, kale, and mache fire their germination in soil down near 40°F, and their seedlings shrug off a light frost. Warm-season crops need warmer ground and die at the first hard freeze. So the question splits in two. What will germinate in cold soil, and what will survive the coldest night before spring.

Dense cold air drains downhill after dark and pools at the base of any slope. A bed at the foot of a hill can sit several degrees below one twenty feet uphill. That is why a single zone tells you little about one specific bed. The number that matters is the low your own ground reaches on the worst night.

A germination range on the packet tells you when a seed sprouts. It says nothing about whether the seedling survives your coldest night. That survival depends on the low your bed hits, which the packet cannot know.

What our own garden did

We garden in zone 7a. Our coldest night in 2026 dropped to 3°F in early January. Our learned station offset runs 7°F colder than the forecast for our area, so a forecast calling for 10°F means we plan for 3°F on the ground. That gap changes what we sow and when.

Early in July we sowed radish across three raised beds. At the end of the month we put lettuce and spinach into the ground bed. Those went in for a fall harvest ahead of our effective first frost. Our offset pushes that first frost to the end of September, weeks earlier than the published date of late October. A gardener who trusted the regional date would sow too late and lose the crop to cold.

The same logic runs the other way for a warmer yard. If your ground holds heat, you can sow later into fall and germinate crops your zone map would rule out. Reading your yard is what tells you which case you are in. The published frost date is a starting guess, and it is often off by weeks.

How to find your yard's real low

You have two ways to pin down the number. Enter a manual offset from what you have watched your yard do, or connect a weather station and let a learned offset build. The free path is the manual offset you set in Settings. When you link a supported station, Siltwell watches how far your readings sit below the forecast and builds the offset from that.

A learned offset needs roughly 14 nights where your station and the forecast overlap. Expect about two weeks before it settles. Once it holds, your frost alerts adjust the forecast low to your station before they fire. That turns a regional warning into a reading for your ground.

With no station and no history yet, the microclimate checker reads recent nights from nearby home stations and reports how far your area runs above or below the forecast low. It works across all recent nights, with a station count and a confidence figure. It reports an area-wide indicator, so your exact bed can still differ.

Pick your crops from what germinates in cold ground and survives your real low, then count backward from your effective frost date to set the sowing week. For a list of what holds through the season in a cold yard, see plants that grow in winter. If you run a station, connect it and let the offset learn so next winter's sowing dates come from your ground rather than a map.