Almost everyone who grows pea shoots soaks the seed first. The real question is what to soak it in: plain water, or one of the biostimulant solutions sold to give stronger germination and bigger harvests. A team at the University of Palermo tested exactly that on pea and arugula microgreens, and the results came out in Frontiers in Plant Science on August 31, 2026.
The headline number: soaked peas produced 53.2% more fresh greens than peas sown dry. Below is what actually went into the soaking jar, why arugula did not respond at all, and how the Italian soak differs from the way peas get soaked on a typical farm.
What the study compared
The team used two biostimulants: a soybean protein hydrolysate (amino acids and peptides, 5% nitrogen) and a seaweed extract. Each went in one of two ways, as a seed soak before sowing or as a root drench. Together with two controls that made six treatments:
- dry seed, watered with plain water (the control);
- soaked in distilled water;
- soaked in the protein hydrolysate;
- soaked in the seaweed extract;
- dry seed, hydrolysate as a root drench;
- dry seed, seaweed extract as a root drench.
Both methods used 3 ml per liter, the manufacturer’s rate. Seeds soaked for 24 hours in the dark at 68°F (20°C). The root drench went in through bottom watering, starting a week after sowing and repeating every two days, five times at 100 ml per tray. The pea variety was Viridios, the arugula Matisse, grown in a peat mix under LED light for 16 hours a day at 64°F (18°C). Everything was cut on day 15, with three replicates per treatment.
Peas: where the 53% comes from
Two treatments tied for the top yield: the water soak (530.9 mg of fresh greens per square centimeter, about 1.1 lb per square foot) and the hydrolysate soak (529.3 mg). The hydrolysate added nothing on top of water. The seaweed soak came in below both. The control, dry peas watered with plain water, gave the lowest yield.
That is where 53.2% comes from: it is the gain of water-soaked peas over dry-sown ones. For the hydrolysate the authors give a separate comparison: soaking in it beat the same product applied as a root drench by 33.3%. Both biostimulants raised pea yield when drenched at the roots, but neither caught up with the two soaked leaders.
The authors credit the gain to faster, more even emergence, so the seedlings start putting on weight sooner. They explain the weaker seaweed soak by composition: seeds take up the amino acids in a hydrolysate easily, while the more complex compounds in seaweed extract get in less readily.
Arugula did not respond
None of the treatments changed arugula yield in any statistically meaningful way. Not soaking, not the biostimulants, not the way they were applied. The authors link this to arugula’s small seed and slower growth.
That matches our seed germination guide: thin-coated seeds like arugula and radish do not need a long soak. Peas, with their thick seed coat, are the crop where soaking pays off.
What the biostimulants did change
They barely moved the harvest weight, but they did change what is in the greens. Seaweed extract raised nitrates and the hydrolysate lowered them, most strongly as a root drench. In peas that meant 26.6% more nitrate with seaweed and 19.9% less with hydrolysate; in arugula, 6.5% more and 24.3% less.
When a biostimulant was combined with soaking, pea vitamin C came out 20.9% above the control. Polyphenols in soaked peas rose 22.8% with the hydrolysate and 21.5% with seaweed, compared with peas soaked in water. Antioxidant activity went up with both biostimulants, whichever way they were applied.
So if a biostimulant does anything here, it changes composition, not pounds. For a grower who sells microgreens by weight, those are two different kinds of value.
How the lab soak differs from a farm soak
The Italian team soaked peas for a full 24 hours and it worked. But the seed containers sat on a shaker at 50 rpm the whole time, so the water kept picking up oxygen. The volume was small too: 40 ml for 35 g of peas (about 1.4 fl oz for 1.2 oz). A day in a jar of still water ends differently: as our germination guide notes, after 12 to 16 hours seeds start to suffocate and rot. For an ordinary soak, keep peas in water no longer than 12 hours, in line with our pea microgreens profile.
A second difference: after soaking, the seeds were rinsed and dried back to their original weight before sowing. On a farm, peas go into the tray wet. The study does not show how that would change the outcome.
And scale. One pea variety, one peat mix, trays of about 6 by 4 inches, three replicates per treatment. It is a single trial, not a rule for every variety and growing medium.
What to do with this
- Soak your peas. The yield gain in the study came from the soak itself, and plain water was enough.
- If you already bought a biostimulant, test it on your own trays: two side by side, one soaked in water, one in the solution, everything else the same. Weigh the cut.
- Arugula did not budge with either soaking or biostimulants in this trial.
- If you track nitrates, seaweed extract pushes them up and the hydrolysate pulls them down.
If your peas turn slimy or start to smell after soaking, our guide to slimy seeds helps tell harmless mucilage from bacterial rot. If they came up in patches, the causes are in the guide to uneven germination.
Soaking pea seeds: key takeaways
- Soaked peas gave 53.2% more fresh greens than dry-sown peas (Consentino et al., 2026).
- A hydrolysate soak matched plain water: 529.3 vs 530.9 mg/cm².
- Nothing tested changed arugula yield.
- Biostimulants change composition: nitrates, vitamin C, polyphenols.
- The study soaked for 24 hours with constant agitation. In still water, keep it under 12 hours.
