Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Growing spring broccoli to acceptable commercial quality standards is a challenge on Delmarva. We are currently conducting a spring broccoli variety trial at the University of Delaware Georgetown research farm with 21 commercial varieties and several experimental lines to evaluate adaptation of these varieties for spring planting.
Temperature variability is the main challenge for spring broccoli. Broccoli is a cool season plant and is best adapted to areas with consistent temperatures during head development where days are warm, not hot, and nights are cool. On Delmarva, high temperatures during head initiation in the spring leads to abnormal floret development. Temperatures more than 88°F can cause damage to florets in sensitive varieties. More heat tolerant varieties have been developed and are being tested our spring trials.
This spring has been cool in general; however, there was a 3-day heat spike over 90°F starting on May 17 that may have challenged some broccoli plantings. In our April 2 transplanted broccoli, we are seeing significant variability in head quality and head disorders between varieties. A second planting was made on April 15 with initial harvest on June 9 and quality so far has been good on earlier varieties.
So far this June has been cool and development has been slowed in broccoli, avoiding another common problem of rapid bolting in high temperatures in spring broccoli in our region. High temperature in later head development causes broccoli to advance so quickly that the crop often flowers before it can be harvested. This reduced harvest window can be a challenge to manage as heads can go from marketable to unmarketable in as little as 24 hours when temperatures are in the 90s.
The following are pictures of quality issues seen in our 2017 spring broccoli trials:
Uniform, well domed head with small beads and good commercial quality in this variety.
Head with uneven bead development, a problem in some varieties this spring.
Lighter blue-green variety showing uneven floret development in this variety. While this head is marketable is is not of highest quality.
Uneven floret development in this broccoli variety placed most heads as second grade.
Uneven floret development and leaf bracts rendered this head unmarketable in this variety.
Open beads and some brown bead caused heads to be unmarketable in several varieties this spring.
Uneven floret development and brown bead in a variety with most heads unmarketable.
Severe brown bead on a variety that is poorly adapted for spring planting.
This variety had high percentage of hollow stem but heads were of high quality.
Results of spring trials with pictures will be posted on our UD vegetable program website after trials have been completed.