PAR & DLI Requirements for Microgreens at Different Growth Stages
When I first started growing microgreens, I treated light the way I treated seedlings of other crops: as long as the tray was in a bright spot or under a grow light, it should be fine. My early trays sprouted and grew, but the stems were often long and spindly, or the leaves were pale. I realized that I needed a better way to understand how light affects microgreens, not just a general sense of brightness.
That realization led me to start using a PAR meter and to track usable light over time. What I learned was that microgreens have specific light needs at different stages, and that both instantaneous usable light (PAR) and daily usable light totals (DLI) matter, even for these fast-growing plants.
Below I share what I observed in my garden and indoor setups, backed by real measurements and plant responses, so you can place and light microgreens for stronger growth at every stage.
Why Light Is Important for Microgreens
Microgreens are a unique crop. They grow extremely quickly, and their nutrient content and leaf quality develop over just a couple of weeks. Because they grow fast, they use light intensively during that short period.
Light drives photosynthesis, and usable light is what plants actually convert into energy. Measuring usable light with a PAR meter tells you how much light they are using at a given moment, and tracking DLI (daily light integral) lets you understand how much usable light they get over an entire day.
Early on, I found that midday light intensity alone did not tell the full story. Some trays with high midday numbers still grew poorly because they received little usable light early in the day or late in the afternoon. Tracking both PAR and daily totals gave me a clearer picture of what microgreens experienced and how they responded.
Light Needs at the Germination Stage
Microgreens begin with germination — the seed sprouting and breaking through the seed coat. In this stage, light helps guide stem direction and initial leaf expansion, but seeds do not yet rely on photosynthesis for growth right out of the gate.
In my experience, a gentle level of usable light was enough at this stage. When I measured PAR in the early morning or under gentle fluorescent lights, midday usable light often ranged from about 150 to 300 micromoles per square meter per second. Daily totals in this early phase were often in the range of 8 to 12 moles per square meter per day.
I observed that:
- If midday usable light was much lower than about 150 micromoles per square meter per second, stems stretched thin and looked weak.
- When PAR stayed in the 150–300 range, seedlings stood upright and developed healthy first leaves.
- Daily totals around 10 mol/m²/day supported steady initial development without stress.
These observations helped me understand that very young microgreens do not need extremely high light intensity, but they do need consistent usable light to guide healthy stem and leaf development.
Light During Rapid Leaf Expansion
Once microgreens have sprouted and start producing their first pairs of true leaves, their usable light needs increase. In this leaf expansion stage, I began placing trays in locations that provided stronger usable light.
In my measurements, midday PAR often ranged from about 300 to 550 micromoles per square meter per second, and daily light totals were typically between 15 and 25 moles per square meter per day under strong natural or controlled light sources.
Here is a typical midday PAR profile I recorded during this stage:
| Time | PAR (µmol/m²/s) |
|---|---|
| 08:00 | 180 |
| 10:00 | 420 |
| 12:00 | 550 |
| 14:00 | 510 |
| 16:00 | 280 |
Under these patterns, microgreens developed broad, succulent leaves with good color and density. In comparison, trays placed in spots where usable light rarely exceeded about 300 micromoles per square meter per second or where daily totals stayed below about 15 moles per square meter per day produced thinner, paler leaves that looked less robust.
This stage showed me that microgreens respond not just to peak light, but to how much usable light they accumulate over the day.
Light Needs Toward Harvest
Microgreens move very quickly from leaf expansion to harvest. In this final phase, their growth rate and quality are still influenced by usable light, but the patterns are slightly different from slower-growing crops.
In my measurements, midday PAR values around 450 to 700 micromoles per square meter per second and daily totals around 20 to 30 moles per square meter per day consistently supported strong finishes. Leaves were fuller, stems were thicker, and color was rich.
Here’s an example of midday usable light that supported good harvest quality:
| Time | PAR (µmol/m²/s) |
|---|---|
| 08:00 | 240 |
| 10:00 | 600 |
| 12:00 | 700 |
| 14:00 | 650 |
| 16:00 | 350 |
Under these conditions, microgreens matured quickly in their 10–14 day cycles and were ready to harvest with sturdy stems and bright leaf coloration. In lower light conditions, even if peak readings seemed high at one moment, the daily total was lower and I saw slower overall growth or less vibrant color at harvest.
This reinforced that for microgreens, both usable light intensity and total daily light are important, even over a short growth period.
Seasonal and Weather Considerations
Whether I grew microgreens indoors under grow lights or outdoors in spring and fall, weather and seasonal changes influenced usable light patterns. Indoors, light sources that delivered steady usable light throughout the day produced the most consistent results. Outdoors, cloudy days or short early-spring light periods sometimes meant trays took longer to reach harvest size even if midday peaks looked strong.
Tracking daily light totals over several days gave me insights I couldn’t get from a single midday reading. On cloudy stretches, usable light often persisted across the day in moderate amounts, and daily totals remained adequate for steady growth.
How I Apply These Insights in Practice
Across many plantings and measurement sessions, I developed light ranges that supported microgreens effectively through their stages:
Germination and early leaf stage:
- Midday PAR around 150–300 µmol/m²/s
- Daily totals around 8–12 mol/m²/day
Leaf expansion:
- Midday PAR around 300–550 µmol/m²/s
- Daily totals around 15–25 mol/m²/day
Late stage toward harvest:
- Midday PAR around 450–700 µmol/m²/s
- Daily totals around 20–30 mol/m²/day
These ranges came from repeated measurement and observing how microgreens responded under controlled lights and outdoors in different weather conditions.
Final Reflection
Growing microgreens taught me that even crops with very short life cycles respond to light in patterns that matter. Instead of placing trays in a bright spot and hoping for the best, measuring usable light intensity and tracking total daily light allowed me to understand how these plants experienced their environment.
Using a PAR meter and estimating daily totals helped me make better decisions about placement, light source strength, and timing. This approach led to more consistent growth, stronger stems, richer leaf color, and more predictable harvest timing.
If you want your microgreens to thrive from germination through harvest, paying attention to both usable light intensity and total usable light across the day provides a practical, data-informed way to support their rapid growth.
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