Seaweed grows: Bok Choy

Bok Choy (Brassica rapa subsp. chinensis) is a nutrient-dense leafy green vegetable that is popular in Asian cuisine. Although considered a cool season crop, Bok Choy yields can be negatively impacted by chilling stress due to its early planting (spring sowing for summer harvest) or late harvest (for summer-sown & fall harvested plantings).

Ascophyllum nodosum, an intertidal seaweed found throughout rocky coastal habitats in the North Atlantic, uses a diverse assortment of bioactive compounds to thrive under intense environmental stresses. Such stresses include extreme temperatures (both hot and cold), drying winds, and high salinity. Extracts of Ascophyllum nodosum have a long history of use mitigating the harm of these same stresses in farmed crops.

In this trial, we applied intermittent chilling stress to hydroponically-grown Bok Choy by setting a marginal temperature for the indoor grow space. We purchased Bok Choy ‘Black Summer’ seeds for the trial from Johnny’s Selected Seeds, and plants were grown in Jack’s Nutrients 12-4-16 RO fertilizer prepared at an EC of 1800 µS/cm and pH of 6.8. We treated half of the plants with buoy™PRO Concentrated Seaweed Extract by diluting the product in their nutrient solution feed at a 0.03% concentration.

The indoor temperatures fluctuated with outdoor temperatures, resulting in daytime temperatures ranging from 60 to 64°F and nighttime temperatures of 56 to 60°F.

Intermittent chilling stress continued for three weeks, after which we adjusted the temperature setpoints to keep daytime temperatures between 64 and 68°F and nighttime temperatures between 60 and 64°F. Plants greened rapidly following the increase in temperatures.

Harvest and Results

We conducted a first harvest on December 05, 2025 to thin the Bok Choy and reduce crowding. The plants treated with buoyPRO took longer to develop symptoms of plant stress, and grew significantly larger than untreated plants by this first harvest date. Treated heads achieved a marketable “baby bok choy” size of 90 g, while untreated heads only average 13.5 g.

The remaining plants grew for an addition 17 days without chilling stress before we harvested them on December 22.

Though untreated plants recovered fully from visible symptoms of stress following the end of the chilling period, treated plants maintained a significant size improvement over the untreated controls at the second harvest date (558 gram average vs 177 gram average).

By reducing the severity of symptoms during stressful conditions, buoyPRO Concentrated Seaweed Extract can help protect your crops from yield losses and harvest delays. As you can see in the charts below, this can translate to significant gains by the end of a production cycle.

Contact us to learn more about out seaweed products, and stay tuned for more updates!