How to transition your greenhouse for a productive winter harvest
As summer crops fade, the mid-October transition is a critical window for gardeners. Moving from summer harvests to frost-hardy winter salads requires more than just new seeds; it demands a careful management of ventilation, moisture, and soil structure to ensure your polytunnel remains productive until late April.
The transition begins in mid-October, typically involving the removal of all summer plants by approximately October 12th to be used for compost. In a no-dig system, the focus is on preservation rather than disruption. Instead of digging or forking—which can destroy natural drainage channels created by worms and disturb vital fungal networks—the beds are simply re-measured, levelled, and given a thorough watering. This approach avoids releasing carbon locked in the soil and maintains the integrity of the soil structure.
Success in the winter months depends on precise timing and environmental control. For the 202-5 season, plantings of lettuce and endive from September sowings, alongside brassicas, can be established by mid-October. Maintaining the right atmosphere is equally vital; greenhouse doors should remain open throughout the winter, except during gales, to ensure proper ventilation. While weeding is minimal, gardeners should watch for self-seeded French marigolds, though natural frost will often manage these.
Watering schedules must shift with the seasons to prevent neglect or over-saturation. In November, watering may be required about once a week, increasing to twice a week in December. By January, watering may not be necessary at all, before increasing again in the spring. If hard frosts are expected, an occasional layer of fleece over the beds can provide necessary protection. If managed correctly, the first harvests can begin in late November, with consistent picking every one to two weeks until the season concludes in late April.
Source: Polytunnel & Greenhouse Changeover | No-Dig Winter Planting, Watering & Ventilation – October 2025
