How to Grow Winter Greens in a Greenhouse

Winter greens thrive in an unheated or minimally heated greenhouse with temperatures between 32-50°F, proper ventilation, and consistent watering.

  1. Create the Perfect Cold Environment. Maintain temperatures between 32-50°F for most winter greens. Install a min-max thermometer to monitor temperature swings. Ensure adequate ventilation with automatic vent openers or manual vents that you can adjust daily. Clean greenhouse glazing to maximize light penetration during short winter days.
  2. Build Your Growing Foundation. Use containers at least 4-6 inches deep with drainage holes. Fill with high-quality potting mix enriched with compost. For larger operations, create raised beds inside the greenhouse. Ensure good drainage as winter greens hate waterlogged soil but need consistent moisture.
  3. Pick Cold-Tough Winners. Select cold-hardy varieties like spinach, kale, arugula, mache (corn salad), winter lettuce, Asian greens like bok choy, and herbs like parsley and chives. These varieties actually improve in flavor after light frosts and handle temperature fluctuations well.
  4. Plant for Continuous Harvests. Start seeds in late summer through early fall for winter harvests. Plant in succession every 2-3 weeks to ensure continuous harvests. Most winter greens take 30-60 days to mature, so plan backwards from when you want to harvest.
  5. Master the Water Balance. Water less frequently than summer crops but maintain consistent soil moisture. Water in the morning so plants dry before evening to prevent fungal diseases. Use drip irrigation or soaker hoses to keep water off leaves. Maintain humidity around 50-70% for optimal growth.
  6. Brighten Short Winter Days. In very northern climates or during the darkest months, add LED grow lights on timers for 4-6 hours daily. Position lights 12-18 inches above plants. Most winter greens need at least 6 hours of light daily to grow well.
  7. Reap What You've Sown. Harvest outer leaves regularly to encourage continued growth. Cut leaves in the morning when they're crisp and full of moisture. Many winter greens are cut-and-come-again crops that will produce for months with proper care. Remove any yellowing or damaged leaves promptly.