Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Broccoli production in the East has gained more interest in recent years. There has been a multistate research and breeding effort underway to develop and evaluate broccoli varieties for adaptation to high density production systems for the Eastern US in an effort to compete with West Coast broccoli.
Broccoli has been grown commercially in our region for many years for large single head harvest that goes to regional and local sales. High density broccoli production is different in that it is geared for medium sized uniform short stem crowns 4.5-5.5” in diameter for the wholesale shipping market. Bunching broccoli is another option and is planted at even higher densities
On Delmarva, the summer planted, fall harvested crop is more reliably grown than a spring planted crop in that temperatures are cooler during head formation reducing the potential for premature flowering that can be problematic in spring planted crops.
Broccoli varieties selected should have tight (dense) domed heads, small bead, and uniform maturity. Color depends on the market, as there are green types and blue-green types. For September-harvested broccoli crowns the varieties should also have some heat tolerance. Avoid varieties that produce hollow stems and that are susceptible to brown bead.
For wholesale production it is most economical to have minimal trips across the field to harvest the crop for any one planting. This is managed by choosing uniform maturing varieties and optimizing populations.
To have a steady supply of broccoli over the fall period, it will be necessary to plant varieties of different maturities, plant at different dates, or do a combination of both.
Direct seeding is possible but can lead to more variable stands. When direct seeding, overseeding and then hand thinning will achieve the most uniform stands. When direct seeding make successive plantings June 20 to July 20.
Most broccoli will be transplanted. Start transplants 4-5 weeks ahead of transplanting. Seed in 72 to 128 cell plug trays or sow in transplant production field beds at 10 seeds per foot of row in rows 12 to 18 inches apart to be lifted as bare root plants.
For high density plantings, for crowns or bunching, highest yields are obtained with narrow rows, 18 to 20 inches apart, plants 6 to 10 inches in the row, for a final population of 27,000 to 34,000 plants per acre. Seed June 20 to July 10 for transplants ready to plant in the field July 20 to August 15. Variety selection is important for the different planting periods. As you get into later plantings in August, switch to shorter maturing varieties.
Broccoli has a high nitrogen requirement: 200 lbs N/A recommended split into three applications – prior to transplanting and 2 additional applications as a sidedressing at 2-3 week intervals. This is critical for high density production. Phosphorus and potassium should be applied according to soil tests. Broccoli also needs additional sulfur and requires 1.5-3 lbs. of boron/A.
Steady, even, irrigation is critical for broccoli production. Soils should not be allowed to dry out more than 30% of the water holding capacity. This is particularly important during warmer periods during the growing season.
High density broccoli can also be grown on raised beds with white plastic mulch and drip irrigation.
A number of herbicides are labelled for broccoli production including Trifluralin, Bensulide, Oxyfluorfen, DCPA, and Napropamide.
Common insect pests include Imported Cabbageworm, Cabbage Looper, Diamondback Moth, and other caterpillars as well as Harlequin Bugs.
Common diseases include Alternaria, Downy Mildew, and Bacterial Head Rot. Common disorders include hollow stem and brown bead.
Broccoli should be harvested when heads have reached the desired diameter (4.5-5.5” for crown harvest) and flower buds (beads) are still tight. Bunched broccoli heads are tied together in groups of 3-4 with a rubber band. Store broccoli and 32°F and relative humidity of 95 to 100 %. Broccoli should be hydrocooled or packed in ice immediately after harvest and kept at 32°F to maintain salable condition.
While average yields for broccoli in our region have been 400-500 boxes (20-23 lb) per acre, high density broccoli has the potential for yields of greater than 600 boxes per acre.
See the Cole Crops Section of the Delaware Commercial Vegetable Production Recommendations for complete production information.