Broccoli thrives in cool weather and rich soils. It is best to grow multiple varieties from transplants. Broccoli is a member of the brassica family and should be planted in an area that has not grown other brassicas (arugula, cabbage, kale, radishes, choi etc) for at least one year for optimum pest prevention. Fall plantings tend to have fewer pest problems and bigger heads.
Broccoli does best in full sun (at least six hours of direct sun). It thrives in rich well drained soil with a pH between 6.0‐7.5. Mix in a shovel full of composted manure, granular all purpose fertilizer and lime to each planting hole.
Planting broccoli from starts usually yields greater success than direct seeding. You can start seeds indoors under lights 6‐8 weeks before last frost. In Portland the seeding window is mid February through March. Harden off seedlings to outdoor temperatures by setting them in a cold frame for a week before planting. If you do not have a cold frame, set seedlings outdoors in the day and indoors at night for a week before planting.
Prepare planting area as described above in the site requirements section. Transplants can go into the garden as early as two weeks before the last frost date (April 15th in Portland). Plant seedlings 1‐2’ apart, and water in with liquid seaweed or B1. Cover your new planting with floating row cover to prevent attacks from cabbage loopers, aphids and other chewing insects that love broccoli.
Broccoli can be directly sown in your garden April through July in the Portland area. Be sure to amend planting area with 4” of composted manure before sowing seeds. Plant seeds 1⁄4 “ deep in rows 24‐36” apart. Seedlings should be thinned 18‐24” apart when they have at least two true leaves.
Seeds for a fall harvest should be started in flats in July and early August. Seedlings can go in the ground once they have 2‐3 sets of true leaves. Broccoli is very sensitive to heat, so plant in the shade of larger summer crops such as cucumbers or potatoes. Transplants can go in the ground through the end of August.
Broccoli can also be grown in containers. Choose a pot at least 12” wide and deep. The soil mix should be 1/3 planting compost and 2/3 potting soil. Varieties such as DeCicco and Packman produce good for pots.
Broccoli needs average evenly moist soil. Do not use overhead irrigation.
Broccoli is a heavy feeder and benefits from a side dressing of composted manure or all purpose granular fertilizer two weeks after transplanting and when the main head begins to form.
There are two types of broccoli. One is the standard with single, large, compact heads commonly seen at markets. The other is the oldest variety called sprouting broccoli that produces many small, shoots. On standard spring planted broccoli, when the central head reaches 1 inch across it should be ready to harvest in about a week depending on weather. Heads should be dark green. If they start to turn yellow they are past their prime.
However, fall planted broccoli is slower to mature and yields larger heads. If day time temperatures are in the 50s or below, you can leave the heads on the plants through the winter and trim off the side shoots. Be sure to cover plants in extremely cold weather.
Many problems that can occur with broccoli are due to weather and cultural conditions. Plants will bolt in reaction to hot weather and drought. They form tiny button like heads if planted when it is too cold. Correct planting time, moderate, consistent moisture, soil amending and row covers are all strategies to maximize broccoli growing conditions.