PAR & DLI Requirements for Brassicas at Different Growth Stages

Brassicas are a family of crops including broccoli, cauliflower, cabbage, kale, and Brussels sprouts. These crops often thrive in cooler climates and have distinct light requirements to optimize leaf, head, or bud development. Managing both PAR (Photosynthetically Active Radiation) and DLI (Daily Light Integral) can improve yield, quality, and uniformity.

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1. Seedling / Early Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	100–200	Light is sufficient to initiate leaf growth and build root systems.
DLI (mol·m⁻²·day⁻¹)	6–12	Helps plants establish without excessive stress.

Tips:

• Use moderate, even lighting to avoid leggy seedlings.
• Maintain temperatures around 15–20 °C to align with brassicas’ preference for cooler conditions.
• Provide consistent photoperiods (14–16 hours) if under artificial lighting.

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2. Vegetative / Canopy Development Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	250–450	Supports leaf expansion and robust canopy formation which later supports head/bud development.
DLI (mol·m⁻²·day⁻¹)	12–20	Helps build biomass and sets the stage for high yield.

Tips:

• Ensure uniform light distribution — avoid shading of lower leaves which can reduce quality.
• Maintain cooler temperatures (< 24 °C) to avoid stress typical of high-heat environments for brassicas.
• Monitor for leaf color and structure — deep green leaves are a sign of sufficient light and chlorophyll development.

3. Head / Bud Formation & Maturation Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	400–650	High PAR supports compact, firm heads and rich pigmentation (especially in broccoli and cabbage).
DLI (mol·m⁻²·day⁻¹)	20–28	Promotes carbohydrate accumulation and reduces hollow-core issues.

Tips:

• A stable, moderate-to-high DLI ensures even head formation.
• Excessive shade can lead to loose or elongated florets.
• Avoid extreme heat or rapid changes in light intensity, which can cause premature bolting (flowering).
• Maintain sufficient airflow and humidity control to prevent tip burn in tightly wrapped heads.

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Light Management Insights

• Cool-season optimization: Brassicas prefer bright, cool light conditions—too much heat under high PAR can inhibit sugar storage in the stems and roots.
• Balanced spectrum: A red-blue balanced LED spectrum (around 3:1) ensures compact morphology and deep green pigmentation.
• Stable DLI: Fluctuating DLI values across cloudy or shaded days may cause uneven canopy growth; continuous DLI tracking helps adjust supplemental lighting in greenhouses.

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Quick Reference Table

Why Monitoring PAR & DLI Matters

Brassicas respond strongly to total light exposure. A single point reading can’t show how light changes through the day — but daily DLI logging reveals the plant’s full light budget.
Monitoring with the AquaHorti AH-PARDLI Bluetooth PAR/DLI Logger lets you:

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Track Light, Improve Consistency

Each brassica species responds differently to seasonal light changes. For example:

• Broccoli prefers consistent, moderate DLI (~22 mol/m²/day).
• Cabbage tolerates higher light, up to 28 mol/m²/day.
• Cauliflower is more sensitive—ideal around 18–22 mol/m²/day to prevent yellowing or loose heads.

With AquaHorti AH-PARDLI, you can:
Log PAR and DLI continuously for 180 days, identifying trends between cloudy and sunny periods.
View the daily PAR curve directly on your smartphone via Bluetooth—no Wi-Fi or account required.
Export CSV data for seasonal comparison and precise supplemental-lighting control.

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Final Thoughts

Brassicas thrive under cool, bright, and stable light. Instead of just relying on “full sun” hours, growers who monitor PAR and DLI gain a clear, quantitative view of their light environment.
Using tools like the AH-PARDLI Logger transforms guesswork into measurable insights—ensuring every crop receives exactly the energy it needs to produce dense, colorful, and high-quality heads.