In The Greenhouse This December

Here are the most useful and timely greenhouse jobs for December — a month focused on protection, hygiene, and keeping winter crops healthy while preparing for early spring sowing: 

🌿 Top Tips for the Greenhouse in December 

❄️ 1. Keep Everything Frost-Free 

• Use bubble wrap insulation on the inside of the greenhouse. 

• Close vents at night and open on mild days for airflow. 

• A small heater or paraffin burner may be needed in very cold snaps, especially if you’re overwintering tender plants. 

🌬 2. Ventilate on Mild Days 

• Condensation encourages mould and botrytis, which are common in winter. 

• Open vents or the door for an hour or two whenever temperatures allow. 

🪴 3. Protect Overwintering Plants 

• Bring in tender perennials (fuchsias, pelargoniums, salvias). 

• Keep compost just moist — overwatering is the biggest killer in winter. 

• Check regularly for rot, mildew, and pests. 

🌱 4. Grow Winter Salads 

Great greenhouse crops in December include: 

• Mizuna, lamb’s lettuce, winter purslane, rocket, winter lettuce

• Water sparingly and harvest leaves frequently to keep plants productive. 

🐌 5. Watch for Pests 

• Slugs, snails, aphids and whitefly can still thrive under cover. 

• Remove hiding places, use sticky traps, and hand-pick pests on mild days. 

• Keep the greenhouse tidy to reduce harbourage. 

💧 6. Water Carefully 

• Water early in the day so plants dry before night. 

• Avoid wetting leaves where possible. 

• Use tepid water if your greenhouse is unheated. 

🧼 7. Deep Clean & Clear Out 

• Remove dead leaves, debris, and any spent plants. 

• Clean staging, benches, and floor to prevent disease build-up. 

• If you have time, wash greenhouse glass inside and out for maximum winter light. 

🧪 8. Prepare for Early Sowing 

December is ideal for getting organised: 

• Wash and sort pots and seed trays. 

• Check your seed stock for dates. 

• Set up a propagator or heat mat if you plan to start chillies or onions early in the new year. 

🧹 9. Check Insulation & Gutters 

• Make sure bubble wrap hasn’t sagged or come loose. 

• Clear gutters of leaves to prevent leaks and damp. 

• Check for draughts around doors and vents. 

🌼 10. Force Bulbs for Indoor Display 

• Hyacinths, paperwhites, amaryllis and narcissus can be forced in the greenhouse for festive flowering. 

• Move indoors once buds show colour. 

🌾 11. Sow Hardy Seeds (Optional) 

If you want to get ahead: 

• Sweet peas (in pots; keep cool but frost-free).