Use case UC07 · Hydroponic Green Oak lettuce

Fewer empty cells, less waiting, more Green Oak seedlings ready to transplant

A Green Oak lettuce study found that some plasma seed-priming methods increased germination and shortened the wait. The next question is whether that gives your trays more transplant-ready seedlings.

Research by Assoc. Prof. Dr. Siwapon Srisonphan and the Plasma Innovations team, Department of Electrical Engineering, Kasetsart University

Sponge seedling tray of Green Oak lettuce in a hydroponic nursery, with empty cells and seedlings of different sizes — A Green Oak seedling tray with empty cells and uneven seedlings · AI-generated illustration, not a research photo

≈95%Germination with submerged EHDP, versus approximately 80% in the control

≈50 hMean germination time (MGT) with submerged EHDP, versus approximately 60 hours in the control

≈30 seedsAdditional germinated seeds per 200 sown, using the study's 80% versus 95%

Figures in this article are laboratory results under the conditions of the cited studies. Results with your own lot or growing system need to be tested.

Uneven seedlings may start at germination

Nursery success is not just germination; it means enough usable seedlings ready for the transplant schedule. Empty cells, late starts and uneven development add sorting, reseeding and scheduling work.

So the first question is not “how many minutes of plasma?” but where your trays lose efficiency, and what to measure:

Empty cells (too few seeds germinate): germination percentage and seedlings meeting specification per 100 seeds
Long waits (slow starts): mean germination time (MGT) and the day seedlings are ready for selection and transplanting
Uneven readiness: the germination window and the number meeting transplant criteria on the same day

Five-step infographic from ungerminated seeds, empty cells and reseeding to uneven seedlings and harder transplanting, with questions to ask before a trial — A problem that starts at germination creates extra work at several nursery stages, so measure the starting problem before choosing an intervention

The Green Oak study compared five seed-priming groups

The primary study by Tephiruk et al. (IEEE Access, 2023) followed Green Oak lettuce (Lactuca sativa L.) from germination to growth in hydroponics. It compared two forms of electrohydraulic discharge plasma (EHDP) priming with hydropriming (water) and osmopriming (KNO₃ solution). ^[1]

Wet-surface EHDP: seeds are briefly soaked in deionized water, leaving a thin surface water layer, then exposed to plasma
Submerged EHDP: seeds are submerged during plasma treatment, then soaked further in the plasma-activated water (PAW) before sowing

Figure 1 from Tephiruk et al. showing the experimental setup, the two seed-priming configurations and the plasma emission spectrum — Figure 1 · Experimental setup, two seed-priming configurations and plasma emission spectrum. Source: Tephiruk et al. (2023), IEEE Access ^[1]

Group	Conditions reported in the study's Methods [1]
Control	No seed priming
Wet-surface EHDP	Soak in deionized water for 1 minute, then expose to plasma for 2 minutes
Submerged EHDP	Plasma exposure while submerged for approximately 1 minute, followed by 12 hours of soaking in PAW
Osmopriming	Soak in 0.5% KNO₃ solution for approximately 12 hours
Hydropriming	Soak in deionized water for 12 hours

Germination tests used 100 seeds per replicate and 4 replicates. The water- and KNO₃-primed groups help show which preparation method drives the difference. ^[1]

Results: more and faster germination

The study's Results report the highest germination percentage and shortest mean germination time for submerged EHDP. ^[1]

Metric	Control	Submerged EHDP	Difference
Germination percentage	≈80%	≈95%	Significant
Mean germination time (MGT)	≈60 h	≈50 h	Significant
Germination window U_75–25 (time from 25% to 75% germination)	≈15 h	≈5 h (both plasma methods)	Not statistically significant

Figure 2 from Tephiruk et al.: graphs of germination percentage, germination window and mean germination time for all five groups, plus day-7 seedlings — Figure 2 · (a) germination percentage; (b) U_75–25 window; (c) mean germination time; (d) day-7 seedlings. Four replicates, mean ±2 SEM; letters compare within each graph. Source: Tephiruk et al. (2023), IEEE Access ^[1]

Submerged EHDP germination differed significantly from the control and hydropriming groups. Wet-surface EHDP had a higher mean than the control but was not significantly different. Table values are approximate, from Results and Figure 2. ^[1]

Keep in mindA lower U_75–25 means germination is concentrated in a narrower interval. However, the plasma groups share statistical letters with the control in Fig. 2(b), so this graph does not establish a significant difference from the control, despite the wording in Results. ^[1]

Keep in mindThe abstract reports 98.3% germination and MGT of approximately 1.87 days, while Results reports 95% and approximately 50 hours. This page uses Results and Figure 2. Exact figures should be checked against raw data before setting any performance guarantee. ^[1]

How plasma changes the water

Plasma changes water properties, and seeds meet that changed environment at their surface. In this dataset, PAW had lower pH than deionized (DI) water and contained measured nitrate and hydrogen peroxide. ^[1]

Measurement	PAW	Note
pH	4.56	DI water: 6.59
NO₃⁻	20 mg/L	Detected concentration
H₂O₂	5 mg/L	Detected concentration
EC (conductivity)	0.014 mS/cm

Figure 3 from Tephiruk et al.: proposed mechanism diagram above, measured water and solution properties below — Figure 3 · Proposed mechanism alongside measured water and solution properties. The hormone diagram is a mechanistic proposal, not a direct hormone measurement. Source: Tephiruk et al. (2023), IEEE Access ^[1]

Read together, these numbers characterize the water the seeds encounter, but lower pH alone does not predict better germination. Water starts imbibition into seed tissues, and plasma-derived species may also affect signaling inside the seed. ^[1]

Keep in mindThe authors propose this mechanism in Figure 3 but did not measure internal seed mechanisms directly, so the main cause of the germination response remains unresolved. ^[1]

How water-borne species affect plants

Nitrate is a nitrogen source and also participates in plant signaling. H₂O₂ can participate in signaling and oxidative responses. Effects depend on concentration and exposure conditions; more is not necessarily better. ^[2]

Kučerová et al. compared PAW irrigation with H₂O₂ and NO₃⁻ solutions in soil-grown lettuce. PAW and a chemically equivalent solution gave similar dry weight but different pigment, photosynthetic and SOD-enzyme responses. Measuring water composition together with plant responses therefore helps explain differences between conditions. ^[2]

After transplanting, growth did not differ

After the nursery stage, the plants were moved into hydroponics and their shoots and roots were monitored. Plant height, root length, stem diameter, leaf thickness and leaf number were similar among groups. ^[1]

Figure 4 from Tephiruk et al.: bar charts of plant height, root length, stem diameter, leaf number, leaf weight, leaf thickness and chlorophyll for the control and both EHDP groups, with photos of a Green Oak head and its roots — Figure 4 · Post-transplant growth of the control and both EHDP groups; n ≥ 4, mean ±2 SE. Source: Tephiruk et al. (2023), IEEE Access ^[1]

Keep in mindBetter germination does not by itself show greater growth after transplanting. The study found clear germination effects but no significant differences in the reported post-transplant growth metrics. Effects on transplant-ready counts and scheduling remain to be followed up. ^[1]

Other work also suggests responses vary by cultivar and growth stage. Jankaitytė et al. plasma-treated seeds of two lettuce cultivars and grew them aeroponically. They saw germination and early-growth responses, but no effect on biomass accumulation or shoot-to-root ratio in either cultivar, while some physiological and biochemical responses differed by cultivar. ^[3]

When to test it in your own trays

Priming is most relevant when the bottleneck begins at germination: low germination, widely spread emergence, high-value seeds or a demanding transplant schedule. To turn germination results into nursery value, track three things:

When are they ready? The day seedlings meet the same size and root-condition criteria
How many are usable? Selected seedlings relative to the initial seed count
How much work does it save? Sorting rounds, working time and cost per usable seedling

Gloved hands lift a Green Oak lettuce seedling in its sponge cube from the tray, showing white roots below — Checking a seedling and its roots before transplanting · AI-generated illustration, not a research photo

Starting from 200 seeds	Germinated seeds
At 80% (control level)	160
At 95% (submerged EHDP level)	190

Using the study percentages, this equals approximately 30 additional germinated seeds per 200 sown. ^[1] However, nursery trials across vegetable species show species-specific responses, so test your actual cultivar, seed lot and growing method. ^[4]

From trial findings to practical use

Establish your lot's baseline first: germination percentage, mean germination time, emergence window and cells needing reseeding. Then split the same lot between your current method and the trial method under the same growing conditions, and measure only what affects transplant-ready output and scheduling.

Current method
Same-lot trial
Count transplant-ready seedlings
Refine conditions
Scale

Five-step pilot roadmap infographic: set a baseline, design control versus treatment, measure key metrics, translate results into operations, and decide to continue, adjust or stop — A small nursery pilot comparing control and treatment, ending in a decision to continue, adjust or stop

The Green Oak results show that priming can change germination count and speed. The next step is to test whether this gives more seedlings ready together when you need them, a question a trial with your own trays can answer. ^[1]

Discuss seed priming for your growing system

Prepare five facts about your nursery and send them to the Plasma Innovations team at [email protected] to design a small trial around your tray problem.

Email the research team[email protected]See other cold plasma use cases →

What to prepare

Cultivar and seed lot
Current germination rate
Trays per cycle
Target transplant date
Transplant-readiness criteria

References

N. Tephiruk, K. Ruangwong, S. Suwannarat, W. Kanokbannakorn, and S. Srisonphan, "Electrohydraulic discharge induced gas-liquid interface plasma for seed priming in hydroponics," IEEE Access, vol. 11, pp. 124634–124642, 2023, doi: 10.1109/ACCESS.2023.3329811.
K. Kučerová, M. Henselová, Ľ. Slováková, M. Bačovčinová, and K. Hensel, "Effect of plasma activated water, hydrogen peroxide, and nitrates on lettuce growth and its physiological parameters," Applied Sciences, vol. 11, no. 5, Art. no. 1985, 2021, doi: 10.3390/app11051985.
E. Jankaitytė et al., "Seed treatment with cold plasma induces changes in physiological and biochemical parameters of lettuce cultivated in an aeroponic system," Agronomy, vol. 15, no. 6, Art. no. 1371, 2025, doi: 10.3390/agronomy15061371.
S. Locatelli, S. Triolone, M. De Bonis, G. Zanin, and C. Nicoletto, "Non-thermal plasma-activated water enhances nursery production of vegetables: A species-specific study," Agronomy, vol. 15, no. 1, Art. no. 209, 2025, doi: 10.3390/agronomy15010209.