Maintaining a greenhouse over winter

Should you be fortunate to have a greenhouse, or be planning one, there is a lot to be done in it over December and early new year, says Linda Lane of Griffin Glasshouses

A Griffin glasshouse

There's always work to be done in a greenhouse, even in December.  Indeed, there's often a lot of colour in this darkest month of the year, with cyclamen, primula, azaleas and other plants destined for the house about to break into bloom in time for Christmas.

The secret to a healthy and successful December greenhouse – heated or not – is maintaining a good ventilation flow. But do watch out for potentially fatal draughts and remember to close doors and windows after a sunny day. Check all plants regularly for signs of disease or infection and treat accordingly. Remove all dead and yellowing leaves and ensure the soil surface is clean and healthy.\

Maintaining a high standard of greenhouse hygiene is very important.  A warm sunny day will quickly create a moist humid atmosphere that's perfect for a variety of potentially harmful pests and diseases. I’ve said it before, but don’t use the greenhouse as an additional storeroom. Leave only essential items and tools inside.

December is rarely the coldest month but has the shortest hours of daylight.  There is still time to insulate the inside of the greenhouse with bubble wrap and clips.  Watering at this time of the year can be challenging as most plants don't need massive volumes and should be allowed to partially dry out. As a general rule, don't leave plants standing in trays of water.

A brief word on pruning greenhouse vines. Once all the leaves have fallen is the time to undertake this work and it's best to seek specialist advice.

It may be December but it’s time to start seed planting in readiness for the 2023 season.  Make sure all seed trays and pots have been washed and disinfected before starting work and that you have sufficient compost. You can begin planting seeds of lettuce, carrots and some French beans but seek out those that are identified as suitable for planting under glass and follow instructions on the pack. If you plan to use a heated propagator, it's essential the tray and clear plastic cover are clean and disinfected, and that all seed trays or pots are similarly treated before you start planting.
Happy Gardening!