Everything moving forward needs a source of power to do so. For growers raising a variety of vegetables, Ben Phillips of MSU Extension thinks broccoli “pulls the train.”

This is true because growers can plant early it early and harvest it late with successive plantings. “This leads to a quest to produce broccoli as long as you can,” he said. He offered some tips and tricks for summer-harvested broccoli (and cauliflower) at the recent Great Lakes Expo.

Of course, these two vegetables have issues with the pests and weather conditions of summer, being crops that do best in cooler conditions. When planting them in spring, with an eye on summer harvest, there are cabbage maggots to contend with, and maintaining quality at head formation is critical. In summer, the cold chain is more important too.

On the bright side, spring-planted broccoli and cauliflower do see relief from autumn Alternaria disease pressure and summer transplant stress.

Cabbage maggot pressure is always higher in spring. To combat that, Phillips suggested waiting a couple weeks after incorporating organic matter for decomposition before planting. Growers can treat plants in trays or in furrow with Verimark at 10 – 13.5 fl. oz./acre or Spinosad at 5 – 10 fl. oz./acre for good control.

He also said to use row covers. “Row covers, while labor intensive, are good for a lot of control,” Phillips noted.

Cole crops evolved from a wild biennial, and broccoli and cauliflower are the developing flowers, Phillips explained. “We want them to ‘flower,’ to get reproductive. We don’t generally think about this because it just happens. Once they grow four leaves, then they ‘listen’ to the temperature. They start accumulating ‘chill’ hours after they reach a certain size. After they vernalize they can go reproductive.”

Ideally, broccoli and cauliflower seedlings should be maintained about 70º in the greenhouse – above their vernalizing temperature. Growers will then want to transplant them early enough to accumulate vernalizing temps below 70º at night and on cool days, with enough warmer daytime temperatures to encourage vegetative growth over a few weeks to initiate flower stalk formation at a gradual pace.

The tricky part is growing the “flower” you want – and one that customers will buy. Phillips talked about the issues that can pop up in summer-harvested plants specifically.

One issue is buttoning. This happens when a plant vernalizes and then is stressed (from root maggots, heat or fertility). If buttoning occurs, the plant is not large enough to support a marketable head.

Stress can also lead to non-uniform beads in broccoli. The plant vernalizes and grows to a good size, then receives inconsistent temperature cues affecting flowering speed. This results in internal bracts (leaves growing through the flower). Internal bracts are easy to snap off, but doing so requires extra work.

In cauliflower, the bits of the flower are called curds rather than beads. Inconsistent temperature cues can affect flowering speed in this plant too. They result in “ricey” heads in cauliflower and internal bracts.

Knowing how to mitigate stressors for spring-planted cauliflower and broccoli can lead to much more successful harvests. Photo by Courtney Llewellyn

Bolting occurs when the plant vernalizes, grows to a good size and then rushes into flower formation from consistent high heat. “This is a furnace-level message to the flower,” Phillips said. It results in a tall, thin flower rather than a round, marketable one.

If a grower sees all leaf and no head, that means the plant did not vernalize. It likely saw consistently warm temperatures during its juvenile period and grows its vegetation without the cues to flower. Phillips said this is seen most often in Romanesco.

So what can growers do? One of the easiest options is managing heat stress with shading and row covers. Proper irrigation and evaporative cooling also work well. White-on-black plastic mulch has shown promise. And there are specific varieties that just tend to handle the stress better.

“Summer-harvested varieties are bred for shorter or higher temperature vernalization periods,” Phillips said. “They also may have a tolerance to high heat after vernalizing to hold their shape as they develop heads.”

For specific varieties, he suggested looking at the Eastern Broccoli Project from Cornell (at hort.cornell.edu/bjorkman/lab/broccoli/easternindustrymain.php) as well as breeder Sakata, Tozer and Johnny’s.

Broccoli varieties that might work well in summer include ‘Abrams,’ ‘Bay Meadows,’ ‘BC1764,’ ‘Belstar,’ ‘Burney,’ ‘Diplomat,’ ‘DuraPak16,’ ‘Eastern Crown,’ ‘Emerald Crown,’ ‘Imperial,’ ‘Lieutenant,’ ‘SV2062’ and ‘Tradition.’

Phillips’s team conducted a trial in 2023 to purposely stress some of these varieties out. ‘Imperial’ did okay but had lots of internal bracts. ‘Eastern Crown’ was ready earlier. And 354B Coronet (from Tozer) did really well, he reported.

As for cauliflower varieties, he recommended breeders Enza Zaden, Bejo and Johnny’s. His team tested the ‘Alcala,’ ‘Bishop,’ ‘EarliSnow,’ ‘Flamenco,’ ‘Melrose,’ ‘Moonshine,’ ‘Nebula,’ ‘Paxton,’ ‘Prestique,’ ‘Puntoverde’ (a Romanesco type), ‘Serenity,’ ‘Snow Crown,’ ‘Synergy’ and ‘Twister’ varieties and found ‘Serenity’ had the nicest picking window – all ready in about one week.

Once everything is successfully grown, maintaining quality at harvest is also critical. Phillips said growers should pick ripe heads in the morning, leaving a long wrapper on cauliflower. After harvest, consider storing heads in waxed boxes, covered to keep the sun off them, and cool everything down further (ideally to 35º) – and keep it cool.

by Courtney Llewellyn