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Broccoli

Planting

Broccoli (Brassica oleracea, Italica Group) is a cool-season vegetable that can easily be grown in the home garden. The crop prefers average temperatures of 65 to 75 F and is best grown in South Carolina during the fall season. While broccoli will produce in the spring season, temperature fluctuations can cause quality issues such as uneven heads and loose clusters of buds. Commercially, these heads are unmarketable but are suitable for home consumption.

Transplanting Dates

Area Spring Fall
Piedmont Mar. 20– April 20 Aug. 15- Sept. 15
Central Mar. 20- April 20 Sept. 1 – Sept. 30
Coastal Mar. 1-April 10 Sept. 1 – Sept. 30
South Carolina Gardening Regions

South Carolina Gardening Regions

Piedmont: Abbeville, Anderson, Cherokee, Chester, Edgefield, Fairfield, Greenville, Greenwood, Lancaster, Laurens, McCormick, Newberry, Oconee, Pickens, Saluda, Spartanburg, Union, and York counties.

Central: Aiken, Allendale, Bamberg, Barnwell, Calhoun, Chesterfield, Clarendon, Darlington, Dillon, Florence, Kershaw, Lee, Lexington, Marion, Marlboro, Orangeburg, Richland, and Sumter counties.

Coastal: Beaufort, Berkeley, Charleston, Colleton, Dorchester, Georgetown, Hampton, Horry, Jasper, and Williamsburg counties.

Harvest broccoli (Brassica oleracea, Italica Group) when the main head is 3 to 6 inches in diameter, and the flower buds are tightly closed. Zack Snipes, ©2020, Clemson Extension

Harvest broccoli (Brassica oleracea, Italica Group) when the main head is 3 to 6 inches in diameter, and the flower buds are tightly closed.
Zack Snipes, ©2020, Clemson Extension

Broccoli transplants can be purchased locally, or a gardener may elect to produce their own. Transplants can be grown in approximately six to eight weeks for the spring, and in about five to six weeks in the fall. See HGIC 1259, Starting Seeds Indoors for information on starting seed indoors. When growing transplants in the spring, be sure to expose them to sufficient cold to harden them off but protect them from temperatures below freezing. Direct seeding is possible, especially for the fall crop.

Plant broccoli in rows 3 feet apart with plants spaced 1½ to 2 feet apart within each row.

Recommended Cultivars

Broccoli is typically marketed by the time during the season in which it does best. For example, early varieties are planted early in the season and produce very quickly, mid-season varieties are planted mid-season, and late-season varieties are planted towards the end of the planting season. Full season varieties can be planted at any point during the planting timeframe. Research varieties for proper timing of harvest dates, as well as to help avoid disease and bolting issues.

  • Packman is an early-season broccoli cultivar (50 days after transplant). In a planting of Packman, most of the main heads will be ready for harvest at the same time. Packman produces many side shoots.
  • Emerald Crown (60 days after transplant) is a mainstay mid-season variety.
  • Lieutenant (60 days after transplant), Belstar (65 days after transplant), and Green Magic (57 days after transplant) are common full-season broccoli varieties with great quality.

Soil

Soils that are well-suited for growing broccoli are fertile, well-drained, and have a texture ranging from sandy loam to clay loam. Soil pH is very important and should be between 5.8 and 6.5 for the best growth. Have your garden soil tested several months prior to planting and adjust the soil pH according to soil test recommendations.

Fertilizing

Performing a soil test is always the best method to determine the fertilization needs of the crop. Information on soil testing is available in the fact sheet HGIC 1652, Soil Testing.

Broccoli is a heavy feeder. In the absence of a soil test, apply 10-10-10 at 2.5 pounds per 100 square feet before planting. Three to four weeks after transplanting, side-dress established plants with calcium nitrate (15.5-0-0) at 2 pounds per 100 feet of row. Apply this second fertilization to direct-seeded broccoli when plants reach 6 inches tall. More frequent side-dressings may be required throughout the growing season for sandy garden soils or when leaching rains occur. Nitrogen is essential to produce high-quality, productive broccoli plants.

Magnesium deficiency is a problem on broccoli leaves during cool, wet periods and is characterized by interveinal chlorosis (yellowing between leaf veins) on older leaves. Correct this deficiency by spraying Epsom salts mixed at two tablespoons per gallon of water directly onto the plant. Repeated applications over a period of weeks may be necessary to correct the deficiency.

Interveinal chlorosis caused by magnesium deficiency. Zack Snipes, ©2020, Clemson Extension

Interveinal chlorosis caused by magnesium deficiency.
Zack Snipes, ©2020, Clemson Extension

Watering

Water the garden to provide a uniform moisture supply to the crop. The garden should be watered in the morning so that the foliage is dry before nightfall. Water sufficiently to moisten the soil to a depth of at least 6 inches. Light sprinklings will encourage shallow rooting of the plants. The critical periods for moisture are during stand establishment and head development. It is important to have a consistent and uniform moisture supply to produce high-quality broccoli and to have the spring crop mature before summer temperatures arrive.

Harvest & Storage

Broccoli is ready to harvest 50 to 90 days after transplanting, depending on the variety. Harvest broccoli when the main head is 3 to 6 inches in diameter, and the flower buds are still tightly closed. Cut the main stem about 6 inches below the top of the head. Some varieties produce many secondary florets in the axils of the stems after the main head has been harvested. Store in perforated plastic bags for up to a week in the refrigerator and freeze any surplus.

Problems

Cole crops, such as broccoli, will “bolt” or produce a flower stalk if exposed to a prolonged cold period of 10 or more consecutive days of temperatures between 35 and 50 F following a period of favorable growing conditions. Bolting is a problem for spring-planted and overwintered crops. The larger the plants are at the time of exposure to the cold period, the higher the incidence of bolting. Sensitivity to bolting also depends on the variety. When planted in the spring, broccoli must be planted early enough to ensure that it is harvested before temperatures become too hot.

To prevent bolting:

  • Grow slow-bolting varieties such as Green Magic.
  • Plant at the correct time.
  • Set out young, healthy transplants that have not been stressed.
  • Water thoroughly when transplanting to start root growth and remove air pockets from the soil.
  • Maintain a steady, moderate rate of growth.

Hollow stem is the most common problem in broccoli. There are two main types of hollow stem arising from two different causes. In the first type, the main stem is hollow, but the inside of the stem is not decayed. This condition is caused by a combination of factors, including excessive nitrogen, warm temperatures, too much water, and low soil pH. Proper spacing, planting dates, and nutrient management can help to alleviate this problem. The second type of hollow stem, the stem is hollow on the inside, but the interior has a brown decay. Using a complete fertilizer that contains boron when preparing the garden to plant can help with this issue. Hollow stem problems can only be treated preventatively, so if it becomes an issue one season, anticipate the problem for the next season.

Another potentially serious problem is tip burn and internal browning. Proper soil pH, proper watering, and the correct balance between nitrogen and calcium will avoid these problems.

Black rot is seen in gardens when moist conditions exist for prolonged periods, and rotation schedules are not followed. Zack Snipes, ©2020, Clemson Extension

Black rot is seen in gardens when moist conditions exist for prolonged periods, and rotation schedules are not followed.
Zack Snipes, ©2020, Clemson Extension

Insects pests, including imported cabbageworms, cabbage loopers, diamondback moth larvae, corn earworms, and cabbage aphids, can be problematic in broccoli. Additionally, flea beetles can severely damage small seedlings. It is crucial to control insect pests before the heads start to develop. Please see HGIC 2203, Cabbage, Broccoli, and other Cole Crop Insect Pests for more information on cultural and chemical control on these insect pests.

In South Carolina, black rot is the most severe disease on broccoli. When temperatures are warm, Alternaria head and leaf blight can also be serious issues. Other common disease problems include downy mildew, bacterial head rot, and soft rot. For more information on diseases of cole crops, refer to HGIC 2202, Cabbage, Broccoli, and other Cole Crop Diseases.

References:

  1. J.M. Kimble. 2020. Southeastern U.S. 2020 Vegetable Crop Handbook.

If this document didn’t answer your questions, please contact HGIC at hgic@clemson.edu or 1-888-656-9988.

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