October 15, 2026

Planting garlic over winter by your yard's real first frost

Plant garlic in fall, in the weeks after your yard's first frost and before the soil freezes hard. The cloves put down roots in cool soil and sit dormant through winter. The cold then triggers each clove to split into a full head. Your own first frost opens that window, and in a cold yard it arrives weeks before the published date. Our garden saw its first cold night of last fall on October 3. The published first frost was October 22, so our yard ran 19 days ahead of it.

Why garlic needs winter

Garlic needs a long stretch of cold before a clove will divide. With too little cold, a clove tends to swell into a single round bulb with no cloves inside. A fall planting lets the roots establish while the soil is still workable. It then gives the clove the whole winter of cold. We planted garlic in our ground bed on March 28 this year and pulled 10 heads on July 31. Those cloves saw only the tail of winter. A spring planting is the fallback when you miss the fall window.

1. Find your yard's first frost date

Published frost dates come from regional records and a forecast grid that can't see your yard. On still nights, heavy cold air slides downhill and settles in hollows, low corners, and enclosed yards, since it weighs more than the warmer air above it. Those spots freeze first. The microclimate checker compares nightly lows from nearby home weather stations against the forecast model over recent nights and gives you a range. It reads your area as a whole, so treat its result as a starting offset for your yard. We cover why the regional date drifts in your last frost date is probably wrong.

2. Shift your planning dates in Siltwell

Any garden owner can enter a manual offset under Settings, then Garden, then Edit garden, in the field called Microclimate offset. A negative number marks your yard as colder than the forecast. Siltwell moves your planning first and last frost dates by that offset, up to 30 days. It also shifts the forecast lows it shows you.

Connecting a weather station lets Siltwell learn the offset for you. Once connected, Siltwell compares the station's outdoor air temperature with the forecast low each night. It trusts the learned offset after about 14 overlapping days. Our station settled at 7°F colder than the forecast. That moved our planning first frost from October 22 to September 30, and our garlic window moved with it.

3. Loosen and feed the bed

Work the bed loose and mix in compost before planting day. Garlic sits in the ground for months, so the soil has to drain. Saturated soil holds little air, and a clove sitting in cold, airless soil rots before it roots. A raised bed drains faster than flat ground. Our notes on compost for raised beds cover how much to add.

4. Plant the biggest cloves

Break the heads apart on planting day and leave the papery skin on each clove. Plant the largest cloves, since a bigger clove stores more food for the roots and the spring shoot. Set each one pointed end up and flat end down. Cover the tip with soil about as deep as the clove is long. Go a little deeper in a cold yard. Space cloves about a hand's width apart so each head has room to fill out.

5. Water them in once

Water the bed after planting. The water settles soil against each clove, so the new roots meet moist soil with no air pockets around them. After that, fall rain usually carries the bed. Water again only if the bed goes dry before the ground freezes.

6. Mulch when the hard nights start

Spread a thick layer of straw or shredded leaves once the cold nights settle in. Mulch slows the soil's heat loss to the night sky. It also evens out freeze and thaw cycles. Those cycles expand and shrink the soil and can push shallow cloves up out of the ground.

Every garden in Siltwell gets frost alerts. At 5 pm local time, Siltwell checks whether tomorrow or the next day will drop to your frost threshold after your offset. When one will, you get an alert in the app, by push, and by email. Treat the first alert after planting as your cue to mulch. Our guide to winter protection for plants covers the other beds that need cover on those nights.

What can go wrong

• Planted too early. A warm fall coaxes the clove into green top growth, and the first hard freeze burns those leaves. The clove then spends stored food replacing them.
• Planted too late. The soil freezes before roots anchor the clove. Freeze and thaw cycles then heave it toward the surface.
• Rot in wet ground. Clay or a low spot that holds water through winter starves the clove of air. Plant in a raised bed or on a mound.

Every frost date in this guide tracks air temperature, including the offset a station learns. Soil gives up heat slowly and freezes later than the air, so your first frost date can't tell you the day your bed locks up. Push a trowel into the bed on cold mornings to see when the top layer turns hard.

In spring the shoots push up through the mulch. Once they're up, rake the mulch back from the stems so the sun can warm the soil. In our garden the last spring frost came on April 30 this year, so we keep the mulch beside the bed into May. If you're planning other cold-season crops around the same frost dates, our guide to winter garden seeds times them the same way.