(This article is written specifically for the CE markets)

Time for strength, not speed – how to prepare plants for autumn
August may still be summer on the calendar, but for greenhouse tomatoes in the Central European markets, it signals the approach of autumn. Days are getting shorter, light conditions are changing, and disease pressure often increases due to fluctuating humidity and temperature conditions typical for CE greenhouses. After an intensive July, the goal is no longer to maximize growth speed, but to maintain strong, healthy plants and reinforce their heads (apexes) and root systems. This investment will pay off during the challenging final months of cultivation.

1. The battle for climate: humidity and cooling
High temperatures and dry winds in August make humidity control a top priority. Proper humidity is essential for bumblebee efficiency and successful pollination.

• Goal: Maintain humidity at 70–80% among the plants.

• Risk: At temperatures above 26–27°C, the natural reflex is to ventilate aggressively. However, opening vents on both sides creates draughts and rapid humidity loss.

• Solution: Use the “dry air influence” function in modern climate computers to control humidity by closing windward vents when necessary.

Ventilation should be set aggressively for cooling—often equal to or below the heating setpoint. Combined with temperature drops (cooler nights and mornings with a “pre‑night”), this helps maintain a flat, stable climate that strengthens plant heads and reduces disease susceptibility.

2. Heating in august? Absolutely necessary
It may sound counterintuitive, but heating in August is essential—not for warmth, but for climate activation.

• Action: Run lower heating pipes (vegetation pipes) for at least 2 hours before sunrise at 40–45°C.

• Purpose: Moving air in the greenhouse prevents dew formation on cold leaf surfaces after sunrise. Dry leaves drastically reduce the risk of Botrytis and other fungal diseases.
  Additionally, a warm pipe improves fruit coloring and overall plant vitality.

3. Precision irrigation strategy
A strong root system remains the backbone of productivity—especially in CE climates where weather shifts can be sudden. In August, irrigation must adapt to shorter days and increased disease pressure.

End of irrigation:

• Stop 3 hours before sunset (10 cm slabs) or 4 hours before sunset (7.5 cm slabs).

• Aim for an overnight slab water content drop of 8–10% (bugger sized tomatoes like pink, beef and standard) by the first morning cycle. 

Night cycle technique:

• If slab water content drops ≥4% within 3 hours of the last irrigation, apply a small night cycle during pre‑night. 
• Benefit: Restores moisture without stimulating the plant, preventing early irrigation that risks fruit cracking and root pressure.

Start of irrigation:

• On Drop: After a 2% moisture drop from sunrise.

• On Light: After reaching 80–100 J/cm² radiation sum.

• On Time: Approx. 2–2.5 hours after sunrise.

Daytime strategy:

• Achieve first drainage early (no later than the 5th hour after sunrise, after 4–5 cycles, at 400 J/cm²). 
• Irrigate on light: approx. 3 ml feed per 1 J/cm² per m².

Advanced end-of-day steering:

• Stop irrigation when radiation intensity drops to 150–200 W/m², or when remaining radiation sum is at least 150 J/cm².

4. Plant care: looking 7 weeks ahead
Trusses forming in August will ripen in 6–7 weeks.

• Use truss supports (arches) to prevent truss breakage.

• Maintain a balanced leaf count—too many leaves increase humidity and increases Botrytis risk.

• Monitor plant disease early: fluctuating CE‑climate conditions often increases risks of powdery mildew, botrytis, and leaf fungal infections.

5. Threats: the “finish clean” principle
August is critical for pest and disease control:

• Low humidity weakens bumblebees; damp nights favor Botrytis.

• Biggest threats: whitefly, Tuta absoluta, spider mites.

• Key task: Eliminate spider mites before they enter diapause. Destroying females now reduces pest pressure next spring.

Summary: A CE‑focused approach
August is not about chasing growth—it’s about stabilizing plants, protecting the canopy, maintaining root health, and ensuring maximum disease resistance before autumn. This article applies specifically to greenhouse conditions in the CE markets, where fluctuating climate and light conditions require deliberate steering.

The information provided by Saint-Gobain Cultilene has been compiled with great care and is intended solely as a guideline for the user. Saint-Gobain Cultilene therefore cannot guarantee any errors and no rights may be derived from the information or advice provided. The user himself is responsible for checking the accuracy and suitability of the information and advice for application. No commercial use may be made of the information and advice provided by Saint-Gobain Cultilene, in whole or in part, without the written consent of Saint-Gobain Cultilene.