Start hardy salads, broad beans, peas, onions and hardy annual flowers. Use a propagator indoors for crops that need dependable germination warmth.
UNHEATED GREENHOUSE PLANTS
Make an unheated greenhouse productive all year.
An unheated greenhouse captures sun and shelters plants from wind and heavy rain, but it may still freeze. Treat it as protection and season extension—not as guaranteed warmth.
What “unheated” really means
Inside temperatures can climb rapidly in sunshine and fall close to the outdoor temperature overnight. A maximum–minimum thermometer shows what your particular structure actually does. Local exposure, glazing, leaks, thermal mass and greenhouse size all matter.
Reliable uses through the seasons
Grow tomatoes, cucumbers, peppers, aubergines and basil once nights are suitable. Ventilation and watering become the main jobs.
Sow spinach, oriental leaves, winter lettuce and herbs while there is enough light for establishment. Remove exhausted summer crops promptly.
Protect hardy salads and dormant plants from the worst weather. Growth is slow because light is limited even when frost is excluded temporarily.
Plants worth considering
Tomatoes, cucumbers and sweet peppers are classic summer choices. Winter salads, spinach, spring onions, parsley, coriander, hardy annual seedlings and early potatoes make use of the cooler months. Always check the individual variety: two cultivars of the same crop can differ in vigour, disease resistance and temperature tolerance.
Frost warning
Glass or polycarbonate does not guarantee frost protection. Keep fleece ready, avoid leaves touching cold glazing and move genuinely tender plants to reliable heat when severe cold is forecast.
Avoid the most common mistake
Do not fill every bench in spring. Crowding blocks airflow and creates a humid leaf canopy. Leave working space and room for the mature size of summer crops.
Explore the plant directory and monthly growing calendar.
What’s happening in your greenhouse?
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Keep growing your knowledge.
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