Glasshouse Climate Blueprints (Common Crops)

This page provides practical baseline climate setpoints for common glasshouse crops. It is designed as a starting blueprint, not a fixed prescription.

Important notes

• Setpoints assume typical UK protected cropping conditions and modern ventilation.
• Adjust for cultivar, crop load, plant size, radiation, CO₂ strategy, and disease pressure.
• Vent strategy uses three values:
• Vent start: when vents begin to open
• Vent target: where vents modulate to hold temperature
• Full vent: temperature where vents are fully open (if possible)

Day periods used

• P1 Early morning (lights up / dawn → ~10:00)
• P2 Late morning (~10:00 → ~13:00)
• P3 Afternoon (~13:00 → ~16:00)
• P4 Late afternoon / evening (~16:00 → sunset)
• Night (sunset → dawn)

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Tomato (fruiting glasshouse)

Temperature setpoints (°C)

Period	Air target	Vent start	Vent target	Full vent	Notes
P1	20	21	23	26	Gentle ramp to avoid shock; protect Ca transport
P2	21	22	24	27	Strong photosynthesis window
P3	22	23	25	28	Avoid overheating; watch VPD/leaf stress
P4	20	21	23	26	Ease down to reduce night respiration
Night	18	—	—	—	Cooler nights preserve sugars; avoid too low in dull spells

Practical strategy - Prioritise stability during fruit set and peak load. - If dull and cool, avoid over-venting: maintain growth with modest temps.

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Cucumber

Temperature setpoints (°C)

Period	Air target	Vent start	Vent target	Full vent	Notes
P1	22	23	25	28	Cucumbers like warmth early
P2	23	24	26	29	High transpiration drives uptake
P3	24	25	27	30	Highest risk of heat stress in sun
P4	22	23	25	28	Don’t drop too fast
Night	20	—	—	—	Too cool slows growth and increases stress

Practical strategy - Cucumber tolerates higher temps but hates stagnation: keep airflow and avoid leaf wetness. - High humidity + warm canopy = disease risk.

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Pepper (Capsicum)

Temperature setpoints (°C)

Period	Air target	Vent start	Vent target	Full vent	Notes
P1	21	22	24	27	Avoid sharp morning swings
P2	22	23	25	28	Balanced growth without stress
P3	23	24	26	29	Peppers dislike extremes; protect fruit set
P4	21	22	24	27	Smooth ramp down
Night	19	—	—	—	Warm enough to avoid stall; not so warm it burns sugars

Practical strategy - Pepper is often VPD-sensitive: avoid overly dry afternoons and overly humid mornings. - Consistent climate beats aggressive pushing.

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Strawberry (glasshouse / tunnels)

Temperature setpoints (°C)

Period	Air target	Vent start	Vent target	Full vent	Notes
P1	18	19	21	24	Gentle start; avoid condensation
P2	19	20	22	25	Protect flower/fruit quality
P3	20	21	23	26	Heat + humidity drives Botrytis risk
P4	18	19	21	24	Encourage drying before night
Night	14–16	—	—	—	Cool nights preserve sugars; avoid cold damp nights

Practical strategy - Strawberry is a leaf wetness + humidity crop: drying the canopy matters as much as temperature. - Use late-day venting to reduce night condensation risk.

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Lettuce (glasshouse)

Temperature setpoints (°C)

Period	Air target	Vent start	Vent target	Full vent	Notes
P1	17	18	20	23	Prevent slow start and wet canopy
P2	18	19	21	24	Avoid pushing too warm (soft growth)
P3	19	20	22	25	Heat increases tipburn risk via imbalance
P4	17	18	20	23	Drop gently for firmness
Night	14–15	—	—	—	Avoid warm nights (softness, disease)

Practical strategy - Lettuce tipburn is often climate-driven (transpiration patterns) not feed-driven. - Avoid extreme afternoon dryness followed by humid nights.

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General venting logic (simple, robust)

• Vent start slightly above target: prevents unnecessary opening.
• Vent target defines the main control band.
• Full vent is your safety threshold: if you hit it regularly, you need shading, airflow, or a different target.

Night strategy (common principles)

• Cooler nights generally improve net carbohydrate gain (lower respiration).
• Avoid cold + wet nights that create condensation and disease risk.
• Avoid warm nights during dull spells (respiration dominates).

Practical troubleshooting cues

• Plants “soft”, stretched: too warm + too humid, or too low radiation
• Blossom end rot / tipburn: climate transport issue (VPD/transpiration), not just calcium supply
• Afternoon wilt with moist substrate: likely VPD / root oxygen / uptake limitation
• Morning disease pressure: leaf wetness duration too long