❄️ Winterizing Your Greenhouse: Keep Plants Safe All Season
Cold snaps, damp air, and low light can stress plants. The good news? With a few simple steps, your greenhouse can stay warm, dry, and productive all winter.
This guide walks you through insulation, airflow, heating, watering, and weekly checks — so your plants stay safe until spring.
1) Pre-Winter Health Check
Clean & Clear
- Remove dead leaves and old compost.
- Wash glazing (inside and out) to boost winter light.
- Disinfect benches, pots, and tools.
Repair & Seal
- Replace cracked panes or damaged polycarbonate.
- Re-seat loose clips; check door rollers and hinges.
- Seal gaps with glazing tape and fresh door brush seals.
Tip: A bright, tidy greenhouse warms faster on sunny winter days and reduces disease risk.
2) Insulation: Bubble Wrap, Seals & Draught Stops
Insulation keeps warmth in and drafts out. Start with clear pathways for light; then add layers where heat loss is worst.
Quick wins
- Line walls with UV-stable horticultural bubble wrap using plastic retaining clips.
- Create a thermal curtain or partition to reduce the heated area.
- Fit door brush seals and draught excluders.
Seal & protect
- Use glazing tape to stop rattling panes.
- Check ridge and eave bolts are snug before storms.
- Weigh down staging covers and floor mats to block under-drafts.
Avoid covering roof vents you still need. Instead, insulate around them so you can vent on mild days.
3) Heat: Passive First, Then Active
Start with passive heat. It’s cheaper and often enough in milder Irish winters.
- Thermal mass: Place water barrels or stone under benches to store daytime heat.
- Fleece & cloches: Add a second “micro-climate” around tender plants at night.
- Capillary mats: Keep roots warmer and watering consistent.
Then add active heat if needed. Aim for frost-free (≈2–5°C) unless growing exotics.
- Electric heaters with thermostats for set-and-forget frost control.
- Paraffin/propane heaters work off-grid; ensure safe ventilation and a CO alarm.
- Heat mats/propagators warm roots with minimal energy use.
Pair heating with insulation first. Otherwise, you’ll pay to heat the outdoors.
4) Ventilation, Humidity & Mould Control
Even in winter, plants need fresh air. However, you should vent gently to avoid heat loss.
- Crack roof vents or doors on mild, dry afternoons to refresh air.
- Use a circulation fan to prevent cold spots and condensation.
- Space plants so leaves can dry; remove yellowing foliage at once.
- Consider a small dehumidifier set to ~60–70% RH in very damp periods.
5) Watering & Feeding in Winter
Growth slows as days shorten. Therefore, water less but more carefully.
- Water in the morning so foliage dries before night.
- Check moisture at root level; avoid wet compost for succulents and cacti.
- Reduce or pause feeding unless plants are actively growing.
- Use tepid water to prevent root shock on cold days.
6) Winter Pests & Disease Prevention
Pests slow down but do not disappear. Consequently, early checks save crops.
- Hang yellow sticky traps to monitor whitefly and fungus gnats.
- Brush down frame joints where red spider mite may overwinter.
- Spot-treat mildew with approved controls; improve airflow to prevent it.
- Quarantine new plants for a week before adding to benches.
7) Power Cuts: Backup Plans
- Keep horticultural fleece ready to cover tender plants on cold nights.
- Use tea-light or paraffin backup heaters only with proper ventilation and supervision.
- Store a torch, batteries, and a simple thermometer you can read without power.
Safety first: Never run fuel heaters without ventilation or a CO alarm.
8) Winter Care Calendar (Ireland: Nov–Feb)
November
- Finish deep clean and install insulation.
- Set heaters to frost-free; test thermostats.
- Sow hardy salads; bring in tender pots.
December
- Vent briefly on mild days to cut condensation.
- Water sparingly; remove any dead leaves.
January
- Inspect seals after storms; re-clip bubble wrap.
- Start chilli/early tomato seeds on heat mats if desired.
February
- Increase venting on sunny days; watch for aphids.
- Top up compost and plan spring sowings.
Next Steps: Make Winter Easy
Ready to winter-proof your space? From bubble wrap kits to thermostatic heaters, we stock the essentials — and we can install them for you.
FAQs
What temperature should I keep my greenhouse in winter?
For most hardy plants, frost-free at about 2–5°C is enough. Raise it for tender or tropical plants as needed.
Is bubble wrap really worth it?
Yes. Horticultural bubble wrap cuts heat loss and evens out night-time dips. Use UV-stable wrap and proper clips for best results.
Should I water less in winter?
Usually, yes. Water early in the day and only when compost is dry below the surface. Over-watering plus low light causes root problems.
