by Courtney Llewellyn

Believe it or not, per a survey of more than 5,000 people conducted by Green Giant in 2021, broccoli was voted America’s favorite vegetable. It was so voted in 2019 too. Because of its popularity, more growers may be considering adding it or expanding their offerings. The problem is that broccoli is a cool season vegetable, and with spring temperatures becoming more erratic – and often warmer – cultivating quality, marketable crops may become an issue.

Anne Carey, graduate student, and Ajay Nair, associate professor, both of the Department of Horticulture at Iowa State University, conducted a recent study to identify appropriate organic broccoli cultivars for late spring planting. Growers in Iowa usually transplant spring broccoli in mid to late April, allowing crops to grow in the cooler temperatures of spring. (The ideal growing temperature for broccoli is between 59º and 65º F.) Higher temperatures often lead to early bolting, increased disease incidence and a high rate of non-marketable heads.

“In spring it can be difficult to predict when high temperatures will occur, and being a busy season on the farm, other events may limit a grower’s ability to transplant at the ideal time,” the study stated. “Depending on market demand, growers are interested in extending broccoli harvest for greater sales into summer. Selecting cultivars to ensure a continuous harvest throughout a season is important in succession planning and therefore farm profitability.”

The goal of their study was to compare the performance – both yield and quality – of six organic broccoli cultivars (Belstar, Covina, Emerald Crown, Green Magic, Gypsy and Imperial) when transplanted in late spring and grown in high summer temperatures. The crops were seeded on March 17, 2020 and transplanted at the ISU Horticulture Research Station in Ames, Iowa, on May 12. The broccoli harvest started July 2 and took place weekly until the final harvest on Aug. 8.

To compare the cultivars, after each harvest the number of heads, the weights of the heads and the head diameters of all marketable/unmarketable heads were noted. (Nonmarketable heads had yellow eyes, brown discoloration, loose heads, beading and bolting.) It was a particularly warm late spring, with maximum temperatures topping 93º between May 12 and June 9.

Belstar had the lowest performance by breaking even, with nine marketable heads and nine nonmarketable heads per plot. Covina had 16 marketable heads to eight unmarketable ones; Emerald Crown, 14 to nine; Gypsy, 15 to nine; and Imperial, 14 to seven. Green Magic performed the best, with 17 marketable heads compared to seven unmarketable ones per plot.

The most common issue with the nonmarketable heads were loose heads, followed by yellow eyes. Belstar bolted noticeably more often than the other cultivars. And while Green Magic had the most marketable heads, they were also the smallest, with an average head diameter of just 3.5 inches.

In other findings, Green Magic and Gypsy had more marketable heads earlier (through mid-July). Covina had more heads in mid to late July. Belstar and Imperial boasted more marketable heads later in the season, from the end of July through Aug. 8. Notably, Emerald Crown presented a steady yield from the beginning to the middle of the growing period.

“This information can be useful to growers seeking to use cultivar selection in a succession plan for late-season planting for extending broccoli harvest,” the study said.

Carey added, “The research is part of a larger organic systems research project investigating the integration of poultry into vegetable production. As the project is on certified organic land, we are rotating the crops each season. In 2021, we completed variety trials of spring grown spinach (yield and Brix) and mini-butternut squash (yield, Brix and storage)” – the results of which will be covered in a future Country Folks Grower.