Growing Wheatgrass and Chives in a Greenhouse: What PAR, CO₂, and VPD Taught Me About Two “Simple” Crops That Behave Very Differently

At first glance, wheatgrass and chives seem easy.
They grow fast, look sturdy, and are often labeled as beginner crops.

But once I started growing both in the same greenhouse — and actually tracking PAR, CO₂, and VPD instead of guessing — I realized how different their needs really are.

They may look similar from above, but environmentally, they behave like two completely different plants.

Here’s what I learned from growing them side by side, cycle after cycle.

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Part 1: Wheatgrass

(Fast, shallow-rooted, extremely sensitive to air dryness)

1. Germination & Early Establishment

(Where wheatgrass dries out faster than you expect)

Wheatgrass germinates quickly, which makes it tempting to give it more light early on. I tried that once — and regretted it.

The result was fast emergence, but uneven height and early yellowing at the tips.

What finally worked for me:

• PAR: 80–140 µmol·m⁻²·s⁻¹
• DLI: ~4–6
• CO₂: 400–600 ppm
• VPD: 0.3–0.7 kPa
• Temperature: 16–20 °C

What I noticed:
Wheatgrass has extremely shallow roots.
If VPD rises even slightly, the leaves lose water faster than the roots can supply it.

Soft light and high humidity made growth uniform and reduced early stress.

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2. Rapid Vertical Growth

(Where wheatgrass grows fast but quality is decided)

Once wheatgrass takes off, growth speed is no longer the issue — leaf quality is.

I tried pushing PAR to speed things up. Yield increased slightly, but leaf texture suffered.

The balance I now stick to:

• PAR: 150–250 µmol·m⁻²·s⁻¹
• DLI: 8–12
• CO₂: 600–900 ppm
• VPD: 0.6–1.0 kPa
• Temperature: 16–22 °C

What changed:

• leaves stayed upright and tender
• color improved
• juice yield became more consistent

Too much dryness caused thin, fibrous blades almost overnight.

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3. Pre-Harvest Stage

(Where restraint matters)

Right before harvest, I stopped pushing growth completely.

• PAR: 120–200 µmol·m⁻²·s⁻¹
• VPD: 0.8–1.1 kPa

This improved texture and post-harvest appearance noticeably.

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Part 2: Chives

(More tolerant, but slower to forgive mistakes)

Chives look tougher than wheatgrass — and they are — but they still respond clearly to environmental imbalance.

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1. Germination & Early Growth

(Where chives hate being rushed)

I initially treated chives like wheatgrass. That didn’t work.

They don’t like excessive humidity, and they don’t like high light early either.

What gave the most stable start:

• PAR: 80–150 µmol·m⁻²·s⁻¹
• DLI: ~4–6
• CO₂: 400–600 ppm
• VPD: 0.4–0.8 kPa
• Temperature: 16–20 °C

What I learned:
Chives need stability more than speed at the beginning.

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2. Leaf Development & Regrowth

(Where chives finally reward patience)

Once established, chives respond well to moderate light and CO₂ — but only if VPD stays in range.

The sweet spot for me:

• PAR: 200–350 µmol·m⁻²·s⁻¹
• DLI: 8–12
• CO₂: 700–900 ppm
• VPD: 0.8–1.2 kPa
• Temperature: 18–24 °C

What improved:

• leaves stayed thicker
• regrowth after cutting accelerated
• yellowing at the base decreased

Pushing PAR higher didn’t help — it just hardened the leaves.

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3. Pre-Harvest & Regrowth Optimization

(Where chives show their real value)

Before harvest, I reduced stress slightly instead of increasing it.

• PAR: 180–300 µmol·m⁻²·s⁻¹
• VPD: 1.0–1.3 kPa

This led to:

• softer cut ends
• faster regrowth
• better uniformity across trays

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What Growing Wheatgrass and Chives Together Taught Me

Growing these two crops side by side made one thing very clear:

• Wheatgrass is fast but fragile
• Chives are slow but sensitive to imbalance
• PAR alone never explains success or failure
• CO₂ only works when stomata stay open
• VPD quietly controls everything

In practice:

• High PAR + high VPD → both crops suffer (in different ways)
• High CO₂ + unstable humidity → wasted effort
• Balanced PAR + moderate CO₂ + stable VPD → repeatable results

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Final Thoughts

Wheatgrass and chives taught me the same lesson in different ways:

Speed doesn’t mean simplicity.

The biggest improvements didn’t come from stronger lights or higher numbers — they came from measuring better, watching how PAR, CO₂, and VPD interact, and adjusting calmly instead of aggressively.

Once I stopped forcing growth and started managing balance, both crops became predictable, consistent, and far easier to grow well.