October 21, 2026

How to prepare your garden for winter by your first frost

You prepare a garden for winter in four passes, and your first frost date sets the timing of each one. Harvest tender crops first, pull spent annuals second, sow cover crops and plant garlic third, and mulch perennials last. The date that matters is the one your own yard gets, and it can sit weeks away from the published date.

October 22 is the published first frost date for our garden. Our station reads overnight lows 7°F below the forecast. With that offset, September 30 becomes our effective first frost. Last fall our station logged frost on October 3, which beat the published date by 19 days. A plan keyed to October 22 would have left tender crops in the beds that night. This guide covers the whole garden in order. For bed-by-bed work, see preparing raised beds for winter.

1. Find your yard's first frost date

Start with the published first frost date for your area. On still, clear nights, cold air sinks because it weighs more than warm air, and it collects in hollows and low corners of a yard. A garden in a hollow runs colder than the forecast, and a bed against a south-facing wall runs warmer.

The microclimate checker looks at how home weather stations near you tracked the forecast model on recent nights. From that it returns a range of offsets for your area. That range describes your area as a whole, so treat it as a starting estimate for your yard. The same logic shifts your spring date, which we cover in your last frost date is probably wrong.

2. Enter your offset and frost threshold

In Siltwell, enter the offset under Settings, Garden, Edit garden, in the Microclimate offset field. Enter a negative number if your yard runs colder. Once the offset is in, your planning frost dates move by as many as 30 days, and the forecast lows in the app move with them. A connected weather station sets the offset itself. It compares its outdoor air temperature with the forecast and needs about 14 days of overlapping readings.

Every evening at 5 pm, frost alerts check the forecast for your garden. If the adjusted low for either of the next two days hits your threshold, an alert goes out. The default threshold is 32°F, and the garden owner can change it.

3. Harvest tender crops on the first alert

Tomatoes, peppers, squash, cucumbers, zucchini, and melons come from warm climates and carry no frost defense. Ice forms inside their tissue and ruptures the cell walls, so one hard frost blackens the leaves and softens the fruit. When the first frost alert arrives, pick everything mature that evening.

• Tomatoes. Pick full-size fruit that has started to pale and ripen it indoors. See putting up tomatoes before first frost.
• Winter squash. Cut it with a stub of stem and cure it in a warm, dry room so the skin hardens for storage.
• Peppers and cucumbers. Pick every usable fruit, because chilled fruit pits and rots in storage.

If a warm spell follows the alert, a cover can carry the plants through one night. Frost cloth traps the heat the soil gives off after dark. See when to cover plants with frost cloth.

4. Pull spent annuals

Once the tender crops are in, pull the dead and dying plants. Aphid eggs, squash bugs, and fungal spores overwinter in old stems and leaf litter, so clearing them lowers next spring's starting population. Compost healthy material. Bag anything with blight or powdery mildew, because a home pile rarely runs hot enough to kill the spores.

Leave frost-hardy crops standing. The lettuce and spinach we sowed on July 29 keep growing through light frosts. Leafy greens build up sugars as nights cool, and the dissolved sugar lowers the temperature at which their cells freeze.

5. Sow cover crops and plant garlic

These two tasks sit on opposite sides of the frost date. Cover crops go in before it. Cereal rye or crimson clover needs a few weeks of growth to root before the soil freezes, so sow each bed as it empties in late summer and early fall. The roots hold soil against winter rain and take up nitrogen that would otherwise leach away.

Garlic goes in after the first frost, once the soil has cooled. Cool soil lets the clove grow roots without pushing much leaf for a hard freeze to burn. Winter cold also triggers the clove to divide into a full head. We planted ours on March 28 this year, and a fall planting gives the cloves a full winter of cold. The timing details are in planting garlic over winter.

6. Mulch perennials after the ground cools

Mulch on perennials keeps frozen soil frozen. Repeated freezing and thawing swells and shrinks the soil, which lifts shallow crowns out of the ground and tears their roots. Wait until the plants are dormant and the top of the soil has started to freeze. Then spread straw or shredded leaves a few inches deep over strawberries, garlic, and perennial crowns.

What can go wrong

• An early frost. A first frost date averages past years, so any single year can freeze well before it. Watch your alerts from a few weeks ahead of your shifted date.
• An area offset in a frost pocket. The checker reads stations around you, and a bed in low ground can run colder than all of them. A weather station placed in that bed measures the yard's own offset within about 14 days.
• Mulch laid too early. Warm soil under mulch delays dormancy and gives voles a sheltered place to nest.
• Water left in irrigation lines. Water expands as it freezes and splits tubing and fittings. Drain the lines first, as in winterizing drip irrigation.

A frost date, adjusted or not, can't tell you how cold your soil is. Soil lags the air by days to weeks depending on moisture and cover, and soil temperature is the cue for garlic and mulch. Push a trowel into the bed before either job.

Your next step is to look up your published first frost date, run the microclimate checker, and write the shifted date on your calendar. Then set each pass against it, with cover crops sown before the date and garlic and mulch after it.