Cabbage, Broccoli, and Other Cole Crops

Soils and Fertilization

Broccoli grows best on a well-drained, medium-to-heavy soil with a high organic matter content. Optimal pH is 5.5 to 6.5. See Soil Management for sources of organic matter and for a description of liming materials. Clubroot affects broccoli unless soil pH is maintained above 7.2.

Fertilization is similar to cabbage with boron or molybdenum additions sometimes required. A ton of broccoli removes 10 pounds N, 3 pounds P2O5 and 8 pounds K2O from the soil. Boron deficiency shows up as blackened hollow stems in broccoli. Magnesium and manganese deficiencies result in pale leaves. All micronutrient additions should be based on soil test results. See Cole crop nutrient recommendations based on soil tests for general recommendations based on soil fertility and Soil Management for organic sources of these nutrients.

Plant nitrogen status can be determined by petiole sap testing. At the six-leaf stage, sap nitrate nitrogen should be 800 to 1000 ppm. When plants have 2-inch heads, sap nitrate should be 500 to 800 ppm and at harvest, 300 to 500 ppm.

Planting

At day temperatures of 60 to 70 degrees F and night temperatures of 50 to 60 degrees F, broccoli transplants are produced in 5 to 7 weeks. Broccoli can be grown using conservation tillage or with cover crops, but is a less suitable candidate than cabbage because of the higher price received early in the season. In broccoli, it is also important to avoid high late spring temperatures (over 68 degrees F) which make it difficult to produce a high quality (tight) head. Rapid growth at high temperatures results in leafy heads, loose clusters and premature opening of flower buds.

In the eastern U.S., broccoli is usually transplanted, especially in the spring because transplanted fields can be harvested earlier and require fewer cuttings. Transplants must be protected from problems with buttoning in the spring. Fall crops head during cooler weather, grow more slowly, and generally produce higher quality (tighter) heads. Light frosts do not hurt broccoli, but buds are damaged by hard frosts.

The more space broccoli is given, the larger the head. Recommended spacings vary from 20 to 40 inches between rows and from 9 to 18 inches in the row, depending on the size head desired for market. If the broccoli heads are to be bunched into a 3-head pack, weighing about a pound, as is usually required for shipping, double rows and reduced in-row spacings (6 to 8 inches) are used to produce small heads with few sideshoots and thin stalks. These spacings also increase yield.

Experiments in Virginia showed that planting with 6-inch in-row spacing yielded 25 percent more fall broccoli per acre (by weight) than 15-inch in-row spacing. All in-row treatments were triple rows planted 18 inches apart with 24 inches between each triple row set. Although average head weight decreased with closer in-row spacings, the increased yield per acre more than compensated for the smaller heads. The same study showed that closely spaced plants did not require greater amounts of nitrogen per acre than widely spaced plants.

Harvest

Broccoli cultivars mature in 45 to 60 days after transplanting. Mature broccoli heads are still compact (tight) and have no yellow color on the flower buds. Overmature heads have a woody outer stem, may show yellow flower color, and have looser flower clusters.

The frequency of harvest depends on temperature, increasing from once a week if temperatures are cool to every 2 to 3 days during warmer weather. After harvesting heads, broccoli stems are trimmed to 6¸ to 8 inches long and the leaves removed. Commercial sales require bunching two to five heads into bundles of 1¹ to 1¸ lbs and binding with rubber bands or plastic collars. There are 14 to 18 bunches per 21 pound moisture-resistant carton. Average yields are 3 to 4 tons per acre in the south. Harvested broccoli must be cooled to 32 degrees F as soon as possible and is normally packed with ice in the cartons. Approximate storage life under these conditions is 10 to 14 days. If ice is not present in the container upon arrival, the shipment may be rejected by the buyer. Broccoli heads produce ethylene, turn yellow and become unsalable at higher temperatures. Ethylene from other produce, such as tomatoes and apples will also cause broccoli heads to yellow.

Buttoning and Other Physiological Disorders

Buttoning or premature formation of a small flowering head is caused by low temperatures. As with cabbage and cauliflower, the exact amount of chilling which will cause flowering is hard to predict and will differ with cultivar, plant age, and the duration of low temperatures. Generally, the plant stem must be at least ¹-inch in diameter and temperatures must be 35 to 50 degrees F for several weeks to induce flowering. High temperatures during the day can counteract the effect of low night temperatures, however, making prediction difficult. Large transplants experiencing long days and stresses from poor drainage, erratic water or nutrient supply, severe traansplant shock, or nitrogen other mineral deficiency are most susceptible: Hollow flower stalks are caused by too rapid growth. This is sometimes confused with boron deficiency, but the latter usually causes browning of the stems as well. Drought-stressed plants are tough and fibrous.

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