PAR & DLI Requirements for Cucumbers at Different Growth Stages

Cucumbers are a popular greenhouse and field crop because they grow quickly, form vines that can be trained vertically, and produce a continuous harvest. To help them reach their potential, it’s important to match light conditions to each growth phase.

Below is a guideline for PAR (instant light intensity) and DLI (daily light integral) targets for cucumbers, along with practical tips.

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1. Seedling / Early Vegetative Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	150–300	Gentle light to avoid leaf burn, yet strong enough to activate photosynthesis
DLI (mol·m⁻²·day⁻¹)	6–12	Provide sufficient daily light for steady leaf and root development

Tips:

• Use fluorescent or low-power LED lighting at this stage.
• Keep lights a bit farther from the plants to reduce hot spots.
• Monitor for pale or elongated stems—these may mean light is too weak.

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2. Vegetative / Vine Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	400–600+	To support strong foliage expansion, node development, and vine elongation
DLI (mol·m⁻²·day⁻¹)	15–25	A solid base of daily light to support vigorous growth

Tips:

• Encourage vertical training (trellises) to allow better light penetration.
• Monitor for pale lower leaves—may indicate light isn’t reaching the whole canopy.
• Prune lower leaves if needed to improve light distribution.

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3. Flowering / Fruit-Set / Fruit Development Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	600–900+	High intensity supports pollination, fruit set, and fruit growth
DLI (mol·m⁻²·day⁻¹)	25–35	Ideal daily light dose to maximize yield and fruit quality

Tips:

• Supplement lighting during early morning or late afternoon to boost daily DLI.
• Monitor fruit set and discard deformed or underdeveloped fruits to allocate resources well.
• Ensure other conditions are optimal—temperature, CO₂, water, nutrients—to make full use of the available light.

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Why These Ranges Are Guidelines, Not Rules

• Local climate, greenhouse glazing, and shading affect actual delivered light.
• Cucumber varieties differ in light tolerance; some heirloom types may adapt differently.
• Other growth factors—temperature, CO₂, water, nutrition—must align with light levels to avoid limiting growth.

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Using AH-PARDLI to Optimize Light for Cucumbers

With a PAR/DLI logger like AH-PARDLI, you can:

• Monitor real-time PAR peaks to ensure your light intensity hits target ranges
• Track daily DLI and compare with ideal values for each stage
• Identify light deficiencies on cloudy or low-light days
• Export data for trend analysis and yield correlations

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Summary Table

Stage	PAR Target	DLI Target
Seedling	150–300 µmol·m⁻²·s⁻¹	6–12 mol·m⁻²·day⁻¹
Vegetative	400–600+ µmol·m⁻²·s⁻¹	15–25 mol·m⁻²·day⁻¹
Flowering / Fruiting	600–900+ µmol·m⁻²·s⁻¹	25–35 mol·m⁻²·day⁻¹

By aligning light conditions with these targets and tracking actual performance, you’ll help your cucumbers reach their full growth potential.