Annual leafy greens grow quickly, are typically more tolerant of shade than fruit bearing vegetables (e.g., tomato and pepper), and do not require a lot of space. They can be grown in small gardens or containers near people’s homes, and are easily incorporated into many traditional dishes for added nutrition. Last year, we evaluated ten varieties (Table 1) of annual leafy greens for their potential to produce large amounts of leafy biomass quickly, grow well in the sub-tropics, and resist bolting (premature flowering and seeding) while still producing seed. Heat tolerance was important to us, so most of the varieties we grew are of Asian origin. In conducting this trial, we became familiar with promising varieties that were new to our seed bank. Based on the results and information summarized below, ECHO staff added four varieties of seed to our seed bank collection, trial packets of which are now available to our international network.
This variety trial was conducted on the ECHO Global Farm in southwest Florida (17391 Durrance Road, North Fort Myers, FL 33917). It consisted of three raised box beds, 60 feet in length. Each bed was divided into ten plots, with each variety randomly assigned to one of the plots within each bed. A plot consisted of three rows of seven plants (giving 21 plants per plot).
The raised beds were weeded on November 10. NPK fertilizer (6% nitrogen-2% phosphorus6% potassium) was broadcastapplied the next day at a rate of 2 lbs per 100 square feet. Seeds of all ten varieties were sown (double-seeded) in fifty-cell flats in the propagation greenhouse on October 19, and were transplanted out to the field on November 17. No other fertilization was given, and no pesticide or fungicide was applied. The plants were watered with drip irrigation approximately two times a week, for two to three hours each time.
Greens were harvested on December 15, December 22, and January 5. (We stopped harvesting on January 5 due to a frost event on January 3 that killed or damaged most of the greens beyond marketability.) Greens were harvested using a small serrated knife, and placed with stems in a bucket of water until we were able to weigh them (weighing happened no more than ten minutes after harvest). We harvested leaves from Toscano Kale, Hon Tsai Tai, and Purple Mizuna, while other more bunched (as opposed to loose-leaved) varieties were harvested as entire heads. They were weighed on a digital scale to a precision of 0.1 grams. The number of plants and cumulative weight of the greens were recorded for each replication of each variety.
After the final leaf harvest, we continued to monitor flowering and seeding of the plants. An informal (non-blinded) taste test of steamed leaves was conducted on January 6. Participants included 13 ECHO staff and interns who identified their favorite varieties and recorded general impressions.
We terminated the trial in the field at 114 days after seeding. Yield data were analyzed with statistical software (SPSS).
Results and discussion
Growth and production: Leaf biomass (weight) at each harvest period varied with crop variety, as shown in Table 1. Because of the frost event on January 3, we were not able to measure the full yield potential of these varieties; however, the data do give an indication of yield potential over a time period (78 days after seeding) that spans the typical time to maturity for these crops.
Table 2 shows the weather conditions under which the plants were grown. Brassicas generally prefer cooler temperatures than warm-season crops such as okra or eggplant, so it is advisable to time the planting of these crops to avoid the hottest months. Temperatures that are too high or low can reduce leaf production by causing the plants to go to seed earlier than they normally would under optimal conditions (known as bolting). According to Knott’s Handbook for Vegetable Growers (Lorenz and Maynard), the optimal temperature range for many brassicas is 60-65°F (16-18°C) with minimum and maximum temperatures of 45°F (7°C ) and 75°F (24°C), respectively. Considering that temperatures in most parts of the sub-tropics and tropics would exceed 24°C, even during the coolest months, we were encouraged that none of these varieties bolted with highs of 25-29°C during their first month in the field. If the climate in your area is too warm for these or similar crops, alternatives may be available (e.g. Malabar spinach [Basella alba or B. rubra]
Based on the information in Table 1, as well as other observations, here are some comments regarding each variety:
Thai Mustard Green leaves began to lose their sweetness and tender texture approximately 64 days after seeding, after which time the plants became spindly and woody.
Japanese Giant Red provided the second largest amount of total biomass among varieties. The plants peaked around 64 days, after which they gained little in biomass and lost some of the leaves’ pleasant flavor.
Big Stem Mustard produced increasingly large stems, which proved to be very palatable. This variety started out small, and had low survival rate due to transplant shock, resulting in the second smallest harvest of the experiment. However, the remaining individual plants produced very well.
Toscano Kale grew slowly into a strong plant. It provided the third-smallest harvest of total biomass, due at least in part to the fact that we harvested the leaves instead of whole heads, which meant that the heavy stems were excluded in our measurements.
Gailan was slower to mature, and stem material composed most of its biomass.
Vitamin Green surpassed all other varieties in terms of total biomass production, (approximately 40% more biomass than the next largest variety, Japanese Giant Red).
Komatsuna produced remarkably uniform
and full heads, and was one of the top producers of biomass.
Hon Tsai Tai was another large producer, with highest biomass production at 78 days after seeding.
Mizuna matured early, but peaked in size midway through the trial. Mizuna was harvested by individual leaves and was a low to medium producer.
Large Leaf Tong Ho produced the least amount of total biomass over its lifespan.
Flowering and seeding: At the time the trial was terminated, five of the ten varieties had flowered, and Hon Tsai Tai, Gailan and Thai Mustard had already begun to set seed. The fact that they flowered, and some even began to set seed, indicates that it may be possible to multiply and save seeds of one or more of these varieties. We have no way of knowing the extent to which the January 3 frost contributed to flowering in these varieties, but at least some of the plants of Hon Tsai Tai, Large Leaf Tong Ho, Gailan and Thai Mustard had begun flowering by December 22, before the frost occurred. Big Stem Mustard began flowering January 19. (Tim Motis observed that an October planting of mustard greens in Haiti, where frost was not a factor, grew well and set seed).
Taste: Large Leaf Tong Ho was a strong favorite among our pool of participants. It was generally agreed that the Tong Ho had a “celery-like” flavor, possibly accounting for its popularity in the taste test. Toscano Kale also scored high (data not shown) in the taste test, which could potentially be due to its more common consumption among our target group. Big Stem Mustard was the highest ranking among the mustard flavored greens in the trial, and received the fourth highest overall rating. Thai Mustard and Mizuna both received low rating, consisting more of stem than leaf tissue.
We recognize the preferences of the participants in this taste test may not translate to the preferences of other populations in other regions of the world, particularly those with a diet that commonly includes more mustard greens.
VanNocker, A. and V. Reed 2012. Annual Leafy Greens Variety Trial. ECHO Development Notes no. 117