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Autumn preparation of the greenhouse for winter

Vse, kar morate narediti v septembru in oktobru za zdrav rastlinjak prihodnje leto.
September 23, 2025 by
Termoplast
Autumn preparation of the greenhouse for winter
Photo by Markus Spiske on Unsplash

Autumn preparation of the greenhouse is the most important moment of the year for long-term usability. What you do in September-October affects the yield of the next spring. Here is our complete checklist.

8-10 hours
total work on 20 m² greenhouse
90%
less disease next year
3-5 kg
winter salads

General cleaning (September)

Start with general cleaning by the end of September:

  1. Remove all plants, tomatoes, cucumbers, eggplants (go to compost or aside, if they are diseased)
  2. Harvest through the soil, remove all roots, weeds and leaves
  3. Clean the structure, cobwebs, dust
  4. Wash the walls with a soft brush and mild solution
  5. Check the seals of windows and doors
Important: Never put diseased plants in compost, burn them or take them to a composting facility. Disease spores (gray mold, phytophthora) can survive up to 5 years in compost.

Disinfection of the structure and soil

Structure:

  • Diluted hydrogen peroxide (3%), safe, effective, without residues
  • Or solution of Marseille soap + baking soda
  • Spray all walls, doors, supports

Soil:

  • Solarization: water the soil, cover with transparent foil for 4-6 weeks in warm spring/autumn, heat destroys pathogens
  • Frost: leave the soil uncovered in winter, frost kills many pests
  • Microbiome: apply EM (effective microorganisms) or compost tea, populate with good microbes

Composting of organic waste

Send all healthy plant waste to compost. Important ratio:

  • Nitrogen (green): fresh plant, grass, tomato leaves
  • Carbon (brown): dry straw, leaves, paper, cardboard
  • Ratio: 1:3 nitrogen:carbon

Compost made in autumn is ready in April-May next year, just in time for spring planting.

More about composting in the article Ecological fertilization without chemistry.

Sowing of winter crops (October)

The greenhouse should not be empty in winter! Good cultures for Sep-Oct sowing:

  • Spinach, frost-resistant, harvest Dec-Mar
  • Winter lettuce (red "Rouge d'Hiver")
  • Polar spinach, real athletic
  • Wild arugula, survives under snow
  • Saffron and carrot (later harvest)

More in the article Winter crops in the greenhouse.

Insulation for winter

By the end of October, check:

  1. Seals of doors and windows, replace damaged ones
  2. Polycarbonate panels, remove dry leaves from between panels
  3. Roof gutters, clean for winter precipitation
  4. Snow support, prepare letvene supports (for polycarbonate roofs for 50 cm snow)
"A greenhouse that is prepared in autumn brings a yield 6 weeks earlier in spring. The one that is not, loses a month.", a gardener from Bohinj

Make a autumn checklist (September-November) and hang it on the greenhouse door, tick off each step as you complete it. The next season will be grateful.

Quality structure = less autumn preparation

Termoplast greenhouses have stainless steel connections and UV-resistant panels, which means 50% less maintenance than cheap alternatives.

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