A guide to growing peppers
Growing peppers in a greenhouse is similar to growing tomatoes or cucumbers, but peppers are especially sensitive to moisture. The short answer: give each plant about 2.25 liters of water per week, spread evenly, and hold soil moisture at a stable 60–80%. All pepper varieties want the same thing — a long, warm, stable growing period. Water needs drop in cloudy, cool weather and rise on warm days; with the GRAAS iRigator automatic irrigation system, holding the range is simple.
| Parameter | Target for peppers |
|---|---|
| Water per plant | ~2.25 L per week, distributed evenly |
| Soil moisture | Stable 60–80% |
| Adjust for weather | Less in cool, cloudy spells; more on warm days |
How to recognize growth disorders in peppers?
If plants wilt, the cause may be too little or too much soil moisture, low soil temperature, salinized soil, or compacted ground.
Yellowing leaves — green parts turn yellow from nitrogen or magnesium deficiency. Compacted soil that restricts root aeration can also cause yellowing, as can iron uptake problems. Lower leaves may yellow with age, and pest damage to roots produces similar symptoms.
Curled leaves — caused by uneven growth (the leaf centre outpacing its width), nutrient deficiencies (potassium and boron affect lower leaves; magnesium, zinc and molybdenum the upper ones), excessive heat, or pests such as spider mites and aphids. Fruits may stay small when growth is too rapid — often driven by temperature extremes or low soil pH.
Examples of pepper growth disorders.
Main pepper diseases and how to prevent them
Fusarium wilt of seedlings — early signs are graying at the base of the stem, softening, then plant death. Causes: infection by Fusarium, Phytophthora or Pythium fungi, excessive watering, low temperatures (10–18 °C) and insufficient sunlight. Prevention: fungicide spraying.
Gray mold (Botrytis cinerea) — the skin separates from the flesh and white-gray fungal growth appears. It develops in cool, damp conditions, when lower leaves aren't removed, nitrogen is overused, or plants get too much water. Control requires fungicides.
Verticillium wilt — wilting, dried leaf edges, and slowed or halted growth. Occurs in infected soil, without crop rotation, or after mechanical damage at planting. Prevention: disinfect soil before planting seedlings.
Alternaria leaf spot — large brown spots (0.5–1 cm) on lower leaves that spread upward; leaves die and dry out, dark lesions form on fruit. Affects seedlings and mature plants alike; favoured by high temperature and excess moisture. Prevention: crop rotation and avoiding overwatering.
Example of leaves affected by Alternaria.
Frequently Asked Questions
How much water do greenhouse peppers need?
About 2.25 liters per plant per week, spread evenly so soil moisture stays at 60–80%.
Why are my pepper leaves curling?
Check three things in order: temperature (too high), nutrients (potassium, boron, magnesium, zinc, molybdenum) and pests (spider mites, aphids). Uneven watering makes all three worse.
Can consistent watering prevent pepper diseases?
Largely yes — gray mold, fusarium and alternaria all thrive on overwatering or moisture swings. Sensor-based watering keeps the soil in range automatically.