PAR & DLI Requirements for Beets at Different Growth Stages

Beets are a cool‐season root vegetable prized both for their edible roots and their greens. While much attention is paid to soil and moisture, light plays a key role in root size, color development, sugar concentration, and foliage health. Here’s a guideline for PAR (Photosynthetically Active Radiation) and DLI (Daily Light Integral) targets for beets across major growth phases — seedling, vegetative, root enlargement, and maturation.

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1. Seedling / Early Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	~100 – 200	Gentle light to support leaf expansion while avoiding stress on young seedlings.
DLI (mol·m⁻²·day⁻¹)	~6 – 12	Enough daily light to initiate healthy greens and root growth without pushing too hard early.

Tips:

• Use moderate lighting (if indoors/greenhouse) or ensure at least partial sun outdoors. For beets, at least ~6 hours of direct sun is recommended.
• Keep seedlings cool (approx. 50–75 °F or ~10–24 °C) since beets are cool‐season crops.
• Avoid excessive nitrogen at this stage — flush foliage but hamper root development.

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2. Vegetative / Leaf Growth Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	~200 – 400	Supporting foliage expansion and root energy reserves.
DLI (mol·m⁻²·day⁻¹)	~12 – 18	Good daily light dose to build canopy, maximize sugar production for root bulking.

Tips:

• Balanced leaf canopy helps efficient light capture — ensure uniform light distribution to avoid shading.
• Be mindful of temperature spikes when PAR is high; root crops like beets do poorly under heat stress.
• Monitor leaf color — pale or yellowing leaves may indicate light or nutrient deficiency.

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3. Root Enlargement / Bulking Stage

Tips:

• At this stage, light becomes increasingly critical for root size and internal quality.
• Avoid excess foliage growth that competes with root development.
• For indoor/controlled systems, ensure supplemental lighting covers this demand especially if natural light is limited.

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4. Maturation / Pre-Harvest Stage

Metric	Typical Range	Notes
PAR (µmol·m⁻²·s⁻¹)	~250 – 400	Moderate to strong light helps finish root color and sugar content without stressing leaves.
DLI (mol·m⁻²·day⁻¹)	~12 – 18	Ensures final quality and root density while avoiding excessive vegetative growth.

Tips:

• As harvest approaches, maintain stable light conditions — avoid major shifts that can affect root texture or color.
• Thin or moderate light slightly if root size is adequate but leaf growth is excessive.
• Consistent moisture and temperature along with light will support best root quality.

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Quick Reference Summary Table

Growth Stage	PAR Target	DLI Target	Key Objectives
Seedling / Early Growth	~100–200 µmol·m⁻²·s⁻¹	~6–12 mol·m⁻²·day⁻¹	Leaf initiation & root set‐up
Vegetative / Leaf Growth	~200–400 µmol·m⁻²·s⁻¹	~12–18 mol·m⁻²·day⁻¹	Leaf canopy development & root energy
Root Enlargement / Bulking	~350–600 µmol·m⁻²·s⁻¹	~18–24 mol·m⁻²·day⁻¹	Maximize root size, color, sugars
Maturation / Pre-Harvest	~250–400 µmol·m⁻²·s⁻¹	~12–18 mol·m⁻²·day⁻¹	Finish root texture and stability

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Why Light Management Matters for Beets

• Beets are cool-season crops; adequate light but moderate heat yield better roots.
• Full sun (at least ~6 hours of direct sunlight) is recommended for optimum root development.
• Insufficient light leads to large greens on top but underdeveloped or spindly roots.
• Proper PAR & DLI ensures plants allocate energy to the root, not just foliage.

Using a device such as the AquaHorti AH-PARDLI allows growers to precisely measure and monitor PAR and DLI levels — ensuring each growth phase receives the targeted light budget.