Insulating Greenhouses and Cold Frames in November

November’s chill makes insulation a top priority for greenhouse and cold frame gardeners. Insulating now keeps vulnerable plants frost-free, saves on heating costs, and helps extend your harvest of salads, herbs, and overwintering crops right into winter. Here’s how to keep your protected spaces warm and productive all season.

Why Insulate in November?

• Prevents frost damage: Protects tender and semi-hardy plants from freezing.
• Retains valuable warmth: Keeps soil and air temperature more stable—less stress for your crops.
• Saves money and energy: Cuts heating needs if you use heaters.

Best Ways to Insulate Greenhouses and Cold Frames

1. Bubble Wrap Insulation

• Use large-bubble horticultural bubble wrap—designed for UV resistance and durability.
• Line the inside of greenhouse glass or polycarbonate with sheets, securing with clips, special fasteners, or lengths of bamboo.
• Overlap seams generously to block drafts.
• For cold frames, staple or pin bubble wrap to the inside of lids and side panels.

2. Fleece or Thermal Blankets

• Drape over benches or wrap individual plants inside the greenhouse as extra frost protection.
• Easily removable on sunny days for ventilation.

3. Draught-Proofing

• Check and seal gaps in doors, vents, and windows with weather stripping or foam tape.
• Repair or replace broken panes or cracked frames to prevent cold gusts.

4. Extra Nighttime Insulation

• Throw fleece or old blankets over cold frames and low tunnel beds each night when frost is likely.
• Remove coverings daily to let in light and fresh air.

5. Insulate the Base

• If using a cold frame on paving or bare earth, add a layer of straw, polystyrene, or old carpet under trays for added base warmth.

Bonus Tips

• Use double doors and hang a temporary curtain or plastic sheeting inside to keep out drafts.
• Add large, full water containers (“heat sinks”) inside your greenhouse—they absorb heat by day and release it at night.
• Group pots and trays together for shared warmth.

Maintenance and Monitoring

• Check insulation regularly for gaps or condensation (wipe away as needed).
• Ventilate on sunny days to prevent fungus and excess humidity, but close up before dusk.
• Use a min-max thermometer to monitor night temps and spot cold spots early.

By insulating now, your greenhouse or cold frame will become a cozy haven for plants—defying frosts and keeping salads, seedlings, and prized ornamentals thriving deep into the dark months.