Autumn transition
Recalibrate your greenhouse for a resilient winter harvest
Fall preparation is more than tidying up. It is a deliberate sequence that purges summer pests, seals in heat, balances humidity, and stages cool-season crops to thrive when daylight wanes.
Phase one · The great greenhouse reset
Begin by dismantling the summer ecosystem. Every step targets pest and pathogen reservoirs so winter crops start in a sterile environment.
Tactical clearing
Remove summer annuals and declining crops. Bag any diseased foliage (powdery mildew, rust, blight) and discard—never compost—to break pathogen cycles.
Deep clean from rafters down
Sweep rafters, ledges, and trellis lines. Collect every leaf, label, and spent string from benches and floors. Rake gravel or cover bare soil with breathable tarp to block weeds.
Sanitise all touchpoints
After debris removal, disinfect benches, trays, irrigation tanks, and tools with quaternary ammonium or hydrogen dioxide. Soak for label-specified dwell time so spores cannot overwinter.
Polish glazing and gutters
Wash glass or polycarbonate inside and out with mild soap and soft cloth; flush gutters and downspouts until water runs clear to maximise winter light and prevent foundation seepage.
Tip: Use the growing calendar generator to plan how soon after the reset you need mature successions staged before the Persephone period begins.
Phase two · Fortify the envelope before the cold arrives
Transition the greenhouse from a summer draft house into a sealed, high-efficiency shell while balancing the side effects of reduced airflow.
- • Inspect frames, joints, and fasteners for corrosion or gaps. Tighten or replace hardware before freeze-thaw cycles stress the structure.
- • Open every door, vent, and louvre; lubricate hinges and test automatic openers so they do not seize in cold weather.
- • Seal drafts with exterior-grade caulk and fresh weather stripping. Focus on panel seams, sill plates, and utility penetrations to preserve heat.
- • Install interior bubble wrap or thermal curtains where light reduction is acceptable. Pair insulation with supplemental lighting plans to offset lower daily light integral.
- • Deploy rodent exclusion: plug holes with steel wool, clear debris around foundations, and set preventative traps to protect wiring and irrigation lines.
Phase three · Revitalise the soil for sustained nutrition
Healthy soil underpins winter productivity. Diagnose, amend, and—when necessary—reset beds before they go fallow in short light.
Test and assess
Send soil samples for pH and N-P-K analysis at season’s end. Note texture (clay, loam, sand) and smell—sour odours indicate anaerobic pockets that require aeration.
Amend for structure and biology
Incorporate 1–3 inches of mature compost or well-rotted manure. Adjust pH with lime or sulphur per lab results, and avoid heavy nitrogen that could push tender growth pre-frost.
Aerate without inversion
Use a garden fork to lift and fracture the top 6–8 inches when soil is moist. This opens channels for oxygen without destroying soil aggregates or fungal networks.
Reset stubborn beds
Solarise beds for 4–6 weeks under clear plastic or steam to 170°F (77°C) for 30 minutes when chronic diseases persist. Re-inoculate with compost afterwards to rebuild beneficial microbes.
Phase four · Build a resilient pest and disease ecosystem
Combine sanitation, exclusion, and preventative biological controls to keep cool-season pests in check and to avoid botrytis flare-ups in sealed spaces.
| Threat | How to spot it | Preventative habits | Organic response |
|---|---|---|---|
| Aphids | Soft-bodied clusters on new growth, honeydew residue, curling tips. | Maintain sanitation, avoid over-fertilising with nitrogen, introduce banker plants for beneficials. | Blast with water, apply insecticidal soap or neem, and release Aphidius wasps or lacewing larvae. |
| Fungus gnats | Small flies hovering near moist media; translucent larvae in top inch of soil. | Allow media surface to dry between watering, improve drainage, deploy yellow sticky cards. | Soil drench with Bti, add predatory mites (Stratiolaelaps scimitus) or Steinernema nematodes. |
| Whiteflies | Tiny white moth-like adults that flutter when disturbed; leaf yellowing. | Fine mesh screens on vents, maintain weed-free perimeter, monitor with cards. | Vacuum adults, spray horticultural oil, release Encarsia formosa parasitoids. |
| Botrytis (grey mold) | Fuzzy grey lesions on flowers, leaves, and stems in humid pockets. | Prune for airflow, heat-and-vent to dry canopy nightly, remove senescing tissue promptly. | Cull infected material, lower humidity, and improve circulation—organic fungicides have limited curative effect. |
Phase five · Master the microclimate
Balance heat retention with humidity relief, and boost light when winter days shorten. Use controllers and data logging to keep adjustments precise.
| Heating strategy | Deployment notes |
|---|---|
| Passive solar (thermal mass + insulation) | Use water barrels, stone, or concrete to absorb daytime heat. Combine with insulated north wall and night curtains. Works best when night lows stay above 25°F (-4°C). |
| Gas hot-air unit heaters | Efficient for large spaces with rapid temperature response. Install sealed combustion units and vent outdoors to avoid ethylene build-up. |
| Hydronic radiant floors or bench heat | Provides even, gentle warmth at root zone. Requires seasonal boiler maintenance and water treatment to prevent scale. |
| Electric supplemental heat | Ideal for zoning propagation benches or as emergency backup. Pair with thermostats and dedicated circuits to manage operating costs. |
Lighting checklist
- • Track daily light integral (DLI). Once natural DLI drops below 10 mol·m⁻²·day⁻¹, supplement leafy greens to prevent etiolation.
- • Deliver 12–14 hours of light using LED fixtures tuned to 400–700 nm PAR; mount 24–36 inches above canopy for uniformity.
- • Integrate timers or controllers so lighting schedules align with heating and ventilation cycles, avoiding abrupt climate swings.
- • Monitor CO₂ levels in sealed structures—consider enrichment to 800 ppm during photoperiod when lights are active.
Phase six · Orchestrate winter planting and succession
Choose hardy crops, plan successions around the Persephone period, and log rotations so pests and nutrient demand stay in check.
| Crop | Hardiness snapshot | Notes |
|---|---|---|
| Spinach | Very hardy (down to 15°F / -9°C with cover) | Sow succession batches through late September; harvest outer leaves continuously. |
| Kale & collards | Very hardy (to 5°F / -15°C) | Transplant mid-summer to size up before short days; flavour sweetens after frost. |
| Carrots & beets | Semi-hardy (roots tolerate 15°F / -9°C) | Direct sow 8–10 weeks before first frost; mulch shoulders and harvest as needed. |
| Lettuce (cold varieties) | Semi-hardy (28°F / -2°C) | Choose winter butterheads and romaines; use inner row cover when nights drop below 25°F (-4°C). |
| Herbs (parsley, cilantro, chives) | Semi-hardy (mid-20s °F) | Pot up divisions near cooler entrances for quick access and natural temperature gradient. |
| Timeline | Key actions |
|---|---|
| August | Remove exhausted summer crops, amend beds with compost, direct sow carrots and beets, start kale and chard transplants. |
| September | Transplant brassicas and chard, sow spinach and lettuce every two weeks, install bubble wrap on north exposures. |
| October | Harvest first successions, thin root crops, deploy internal row covers, calibrate thermostats and humidistats. |
| November–January (Persephone period) | Hold mature crops in place, harvest as needed, maintain logs for temperature, humidity, and pest scouting. |
Track rotations in your garden log so brassicas, alliums, and legumes cycle through different beds each season. Pair with the heating cost calculator to forecast fuel needs for your chosen night temperatures.
Phase seven · Close the loop
- Sharpen and sanitise tools with 70% alcohol; oil hinges and drain irrigation lines before storage.
- Take inventory of supplies (compost, fertilisers, row covers) and restock during off-season to avoid shortages.
- Record lessons learned—successful varieties, pest outbreaks, energy usage—to fine-tune next year’s fall sequence.
Connect the next steps
Use these resources to extend your fall plan:
- Climate control blueprint for deeper heating, humidity, and ventilation strategies.
- Spring planting calendar to transition from winter harvests into early sowings seamlessly.
- IPM blueprint for comprehensive biological control tactics.
Frequently Asked Questions
When should I start fall greenhouse maintenance?
Begin structural inspections and sanitation in late summer so repairs, sealing, and heater servicing finish before consistent cold arrives. Schedule professional heater checks at least four weeks before you depend on them.
How do I stop high humidity after sealing the greenhouse?
Run horizontal airflow fans continuously and use short, automated exhaust cycles governed by a humidistat. Aim to keep relative humidity below 80% overnight by pairing heat-and-vent routines with morning irrigation.
Do I need supplemental lighting in autumn?
Yes once day length drops below 11 hours or crops show stretch. Provide 12–14 hours of full-spectrum light for greens and pair lighting with CO₂ monitoring so plants can utilise the additional energy.
What is the quickest way to revitalise tired soil?
Topdress with two inches of quality compost, fork to relieve compaction, and irrigate thoroughly. For persistent diseases, steam or solarise, then reintroduce beneficial biology with compost or microbial inoculants.