Ice plants grown in individual deep-water culture (DWC) buckets at Cornell University.

Ice plant (Mesembryanthemum crystallinum L.) is a novel salad green noted for its glistening appearance and succulent and savory taste. It is a salt-loving plant native to sea coasts in South and East Africa, the Sinai, and Southern Europe, and is naturalized in Mediterranean coastal areas, the U.S., Australia, Mexico, Chile, and the Caribbean. Its name comes from the special epidermal bladder cells (EBCs) covering the entire surface of the plant. These cells contain water and accumulate mineral salts, especially sodium chloride (NaCl), and play a role in the salt tolerance of ice plants. The cells also reflect light and look like ice crystals under the sun.

Ice plant has high nutritional values to humans due to its distinctive phenolics and polyols that are reported to burn fat, reduce blood sugar, and reduce the risk of atherosclerosis and diabetes.

With controlled-environment agriculture (CEA) growers looking to expand their offerings, and consumers looking for interesting new plants, many greenhouse and indoor vertical farming growers have also added ice plant to their list of production. However, little information is available on cultural practices. This article begins with general plant culture, and then recaps studies at Cornell University to determine how this coastal plant grows with increasing sodium chloride in the nutrient solution, and how this affects consumer preferences.

Ice plant is typically harvested at seven to eight weeks old. Seeds can be started in rockwool or other soilless substrates, and it is ready to transplant at three to four weeks of age when seedlings have four to five true leaves. Ice plant can tolerate a relatively wide range of temperatures, but 68°F to 86°F is optimal. Higher temperatures can cause a lower germination rate and stunt growth. Ice plant prefers full sunlight. Although ice plant can tolerate some drought, regular fertigation is recommended. However, the substrate should be well-drained, or if grown hydroponically, dissolved oxygen should be maintained in the root zone. In addition, ice plant prefers low to mid relative humidity (30% to 70%). High humidity may cause rot or fungal problems. For hydroponic growers, various systems including deep water culture (DWC), nutrient film techniques (NFT), and aeroponics can be used to grow ice plants.

Ice plant can store abundant water and NaCl in its EBCs. This characteristic brings a special succulent and savory taste. In fact, ice plant requires a saline environment for optimal growth. Unlike any other hydroponic leafy greens or herbs, it is common for growers to add NaCl in their substrate or hydroponic solution for ice plant.

Research was done at Cornell University on the response of ice plant to different concentrations of NaCl in hydroponic nutrient solution. The research was conducted in a controlled-environment greenhouse (73°F day temperature, 70°F night temperature, and 14 hours daylength). The plants were cultivated in mini deep-water culture hydroponic systems and fed with 150 ppm N (combining equal parts 5 N – 12 P – 25 K Jack’s Professional Water-Soluble Fertilizer and 15.5 N – 0 P – 0 K [calcium nitrate]). Five different NaCl concentrations were added to the hydroponic nutrient solution in ppm Na/Cl: 0/0, 1150/1775, 2300/3545, 4600/7090, and 9200/14180. To put these high salt concentrations into perspective, the highest treatment is two-thirds as salty as seawater, and electrical conductivity measured 42.3 dS/m, which is 23.5 times stronger than the standard nutrient solution.

Closeup of ice plant epidermal bladder cells.

Results showed extraordinary growth benefits of adding 1140/1775 ppm NaCl. Plants treated with 2300/3545 ppm NaCl also performed much better than the control (no salt). Further additions of NaCl decreased plant size. With increased NaCl concentration in the hydroponic solution, increased NaCl content was detected in the leaf tissue.

As a conclusion, adding 0.05 to 0.10 mol/L NaCl is recommended for the hydroponic production of ice plant. By manipulating NaCl concentrations in the substrate/hydroponic solution, growers can create various salinity categories when marketing ice plants.

Following the trials with salt concentration, a consumer sensory evaluation was conducted at Cornell University to quantify how consumers like ice plant grown in varying NaCl concentrations in hydroponic solution. A total of 115 participants were invited to taste five ice plant samples grown with the same five NaCl treatments described above. Panelists were asked to evaluate the appearance, flavor, texture, and aftertaste of ice plant, as well as their familiarity with ice plant and purchase intent.

Results showed that people were able to differentiate the salt intensity of the five samples. Plants treated with 0/0, 1150/1775, and 2300/3545 NaCl received similar “overall liking” scores (moderate scores, 5 out of 9 points). Plants treated with higher NaCl concentrations received slightly lower “overall liking” scores.

When “overall liking” was divided up into the components of “flavor liking”, “appearance liking”, and “texture liking”, we found that flavor is the only factor that affected overall liking. Additionally, with increased NaCl concentration, panelists sensed slightly more sourness and fishiness, and slightly less green flavor. Bitterness and sweetness were not affected by the salt level. Most people did not detect aftertaste, and for those who did, most thought the aftertaste was acceptable.

With regard to familiarity and purchase intent, most panelists were not familiar with the ice plant, and the purchase intent was relatively low. However, in the open question asking what occasion or situation you would find yourself eating this plant, most people noted they would expect it in restaurants used as a salad or side dish. In general, more work needs to be done on marketing and nutritional research of ice plant.

Besides its use as an interesting edible leafy green, ice plant may be a beneficial companion plant in hydroponic systems. In DWC or NFT systems, sodium and chloride can accumulate over time as new water is added to the system. Since ice plant accumulates NaCl, it could be used to bioremediate the hydroponic water, thereby removing NaCl so that more sensitive plants such as lettuce can thrive. More work is needed to test this application. If proven, a grower can get a novel leafy green and keep their hydroponic water filtered for NaCl.

Jiaqi Xia is a Ph.D. student within the School of Integrative Plant Science at Cornell University. Mattson directs Cornell’s Controlled Environment Agriculture program. See all author stories here.

The Voice for Controlled Environment Production