Family: Brassicaceae
Genus and Species: Brassica oleracea
Climate
Broccoli is often referred to as a cole crop. Broccoli thrives in cool weather and can withstand light frosts. Flavor improves with cooler temperatures because plant cells are working to convert starches to sugars to protect the plant against the cold. The result is a sweet, fresh taste that surpasses that of store-bought greens.
Broccoli does not normally do well in hot weather though more heat tolerant cultivars are being developed.
Soil
Crop rotation is especially important with Broccoli and other members of the Brassicaceae (previously referred to as the Cruciferae or crucifer) family that includes kale, radish, mustard greens, turnips, and Brussels sprouts. 2 - 4 years between plantings of the same family is recommended.
Broccoli plants will grow in almost any soil but prefer a pH between 6.0 and 7.0 for optimum growth. A pH within this range will discourage clubroot disease and maximize nutrient availability. Well-drained, sandy loam soils rich in organic matter are ideal for broccoli plants and especially early plantings of broccoli.
Spacing
Broccoli yields and the size of broccoli heads are affected by plant spacing. The tighter the spacing the better the yields but the broccoli heads will be smaller.
For an average head of broccoli (approx. 8 oz.) plants should be 8"-10" apart with 30"-36" between the rows.
Some growers use and alternate spacing of 12"-24" between broccoli plants with an 18"-36" spacing between rows.
Direct Seeding
A well-prepared seedbed with adequate moisture is a must for direct seeded broccoli. Sow broccoli seed 1/4" deep, every 8"-10" within rows set between 30"-36" apart. Gently press the soil after planting to ensure the seed is in contact with the soil.
Broccoli may be direct seeded in both spring and fall. Sow the spring crop 4 weeks before last spring frost or as soon as the soil can be worked - whichever is later.
Seeding For Transplants
Sow broccoli seed into flats, cells, or soil blocks of soil-less mix. Avoid crowding the seeds. Provide 1-1/2" to 2-1/2" square inches per plant. Ideal temperatures for broccoli growth are between 50°F at night and 85°F during the day. Begin hardening off the seedlings seven days before transplanting.
Germination
These seeds germinate best in soils around 75°F-85°F.
Germination will take 4-20 days.
Transplanting Into the Garden
Transplant broccoli plants at 6-8 weeks, 4 weeks before to 2 weeks after the last spring frost. Broccoli seedlings should be 8"-10" apart with 30"-36" between the rows.
Watering
An even moisture supply is needed for broccoli transplants to become established and to produce good heads. Never let the seedbed dry out. In sandy soils this may require two to three waterings per day. You must maintain adequate moisture until broccoli seedlings are well established.
Harvesting
Harvest broccoli heads when the buds are still small and tightly closed. Broccoli heads should not have any yellow petals. Side heads will develop rapidly in some varieties after the main head has been harvested. Harvesting of the broccoli side heads may continue for several weeks.
Post-Harvest Handling
Broccoli is highly perishable. The respiration rate of freshly harvested broccoli is very high and it is therefore necessary to hydro cool broccoli very soon after harvest and to keep it cool. Hydro cooling is the process of spraying or immersing vegetables in chilled water.
Storage
Store broccoli at 32°F with a relative humidity of 95% to 100% to maintain its fresh green color and vitamin C content. Store broccoli with adequate air circulation. Broccoli should keep for between 10 to 14 days under ideal conditions.
Broccoli should not be stored with fruits, such as apples or pears, which produce substantial quantities of ethylene, because this gas accelerates yellowing of the buds.
Diseases
Club Root, Black Rot, Black Leg, Wirestem, Alternaria Leafspot, and Downy Mildew
Pests
Aphids, Cabbage Loopers, Imported Cabbageworm, Cutworms, Flea Beetles, and Diamond Back Moth
Comments
The trick to producing excellent broccoli heads is to keep the broccoli plants growing at a steady pace. Top-dress the plants with compost or manure tea; or side-dress with blood-meal or fish emulsion; and water deeply. Repeat this process every 3-4 weeks until just before harvest.
Mulch will help keep the ground cool and moist as well as reduce weed competition.
References
Weekend Gardener, "Broccoli", Chestnut Software, Inc, http://www.chestnut-sw.com/seeds/vegseed/broccoli.htm, Accessed 2003-01-01.
Riofrio, M., "Growing Broccoli and Cauliflower in the Home Garden", Ohio State University Extension Fact Sheet, HYG-1605-92, http://ohioline.osu.edu/hyg-fact/1000/1605.html, Accessed 2003-01-01.
Oregon State University, "Broccoli, Commercial Vegetable Production Guide", Last modified 2002-12-26, Oregon State University, http://www.orst.edu/dept/NWREC/broc-pr.html, Accessed 2003-01-01.