August 3, 2026 · Updated September 12, 2026

How to overwinter chilli plants before frost hits

Chillies die at the first hard frost. When the air reaches freezing, the water inside the leaves and stems turns to ice, the cells rupture, and the plant collapses within a day. To overwinter a chilli you move it indoors before the first freezing night reaches your own yard, and that night lands earlier than the regional frost date in most gardens.

Why frost kills a chilli plant

Chillies are tender perennials from warm climates. They hold no dormancy and no antifreeze in their tissue, so they have no way to ride out a freeze. At 32°F the water in the leaves and stems freezes, the ice tears the cell walls, and the plant goes limp and black over the next day.

They suffer long before the killing frost too. A chilli stops growing and starts shedding flowers and fruit while the air is still well above freezing. A plant left out through a cold snap often looks half-gone before the frost that finishes it.

Why your first frost beats the calendar

On a still, clear night cold air sinks because it weighs more than warm air. It slides downhill and gathers in low spots and along fences and walls. That is why one corner of a garden frosts while the rest stays green. The forecast low reports the air a few feet up. Your pots sit in the colder pocket below that reading.

Radiative cooling stacks on top of this. After sunset the ground and the plants give their heat back to the open sky, and a leaf surface can drop several degrees below the air the forecast measured. A predicted low a few degrees above freezing can still leave frost on the foliage. The published frost date is an average across a wide region, so your yard carries its own number. We walk through why that date misleads in this guide on last frost dates.

What our garden shows

Our published first fall frost is 10-22. In our own garden the first fall frost landed on 2025-10-03, about three weeks earlier than the printed date. Our site runs a learned 7°F colder than the forecast, so our effective first frost sits near 09-30 rather than late October. We garden in zone 7a.

That gap changes the move date directly. We planted a bell pepper in a raised bed on 05-22 and pulled the last of its fruit by late August. A plant we wanted to keep would have needed to come inside near the end of September, well before the calendar warned us. Timing to the region here would have cost us the plant.

How to time the move to your yard

The safe move date is the night your yard first hits freezing, adjusted for how cold your ground runs. There are three ways to find that number:

• A manual offset. Enter how much colder your site runs in settings, and the frost alert shifts the forecast low to match your yard.
• A learned offset. A connected station compares its own readings to the forecast and learns the gap after about 14 overlapping nights, then applies it for you. Connecting a station turns a manual estimate into a measured one.
• The microclimate checker. Without a station, the microclimate checker reads what nearby home stations logged on recent nights, sets those against the forecast, and tells you how much colder your area tends to run.

Once your low is adjusted, the frost alert fires when the coming night drops to or below your threshold, so the warning arrives the day before the freeze rather than after it.

Pick the plants you want to keep now, cut them back, and stage them near the door. Set your frost alert to your yard's adjusted low so the warning matches your first freeze rather than the region's average, and move the pots inside the afternoon before that night.