How do I protect garlic from extreme winter conditions?

Published: Mai 03, 2025
Updated: Mai 03, 2025

When growing garlic during polar vortexes, you'll need to put a little thought into how you'll insulate the crop. A sleepy six inches of straw mulch acts as a snowshoe for the ground; the intervening air pockets serve to temper the roots. My Montana garlic survived -35F (-37C) with this material on it, while other rows without mulch were frozen solid.

Insufficient Mulch Depth

  • Less than 4" allows frost penetration
  • Causes heaving that breaks roots
  • Doubles winter kill rates

Wrong Materials

  • Leaves mat and suffocate shoots
  • Plastic traps moisture causing rot
  • Hay carries weed seeds
Mulch Material Insulation Values
MaterialStrawDepth6" (15cm)R-Value2.5 per inchBest ForExtreme cold (<0°F/-18°C)
MaterialShredded LeavesDepth8" (20cm)R-Value1.8 per inchBest ForModerate winters (10-32°F/-12-0°C)
MaterialBurlapDepthLayer over strawR-ValueBlocks windchillBest ForWindy sites
R-values from University of Maine Cooperative Extension

Apply mulch when soil temperature drops below 40°F (4°C). Insulation of soil early delays dormancy. I learned this in November 2021 when a warm spell caused garlic to sprout under mulch and then it froze. Less than ideal. Wait until 3 frost events that indicate consistent, steady cold.

Early Stage

  • Clear 2" when shoots emerge
  • Leave 4" around base
  • Prevents stem rot

Mid Spring

  • Remove all mulch at 60°F (16°C) soil temp
  • Compost decomposed material
  • Check for vole nests

Microclimates shift strategies. I have been planting garlic near a south-facing property stone wall, which absorbs the sun's rays and radiates heat, especially beneficial in spring. When I had livestock, I used their panels as windbreaks. The holes in panels make the flow of air more turbulent compared to solid panels. And every 1,000' (305m) of elevation distally moves my mulching temperature down another 1" (2.5cm).

Spraying kelp extract onto frost-damaged garlic will stimulate recovery at thaw. The recovery is likely due to the presence of cytokinin in the kelp extract. In the Minnesota trial, 75% recovered red versus 20% of untreated garlic recovered. Combined with black landscape fabric provides warmth to the soil and is to be removed once the temperature stabilizes.

Read the full article: How to Grow Garlic Successfully in Any Climate

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