When to Plant
Transplant young, vigorously growing plants in early spring. Transplants are recommended to give the best start for spring planting, because transplanting gets the plants established more quickly. Thus they can bear their crop with minimal interference from the extreme heat of early summer. Plants that remain too long in seed flats may produce "button" heads soon after planting.
For fall crops, buy or grow your own transplants or plant seeds directly in the garden. For fall planting, start seedlings in midsummer for transplanting into the garden in late summer. Fall crops may be direct-seeded in the garden if space allows or may be started in flats to replace early crops when their harvest ends.
To determine the best time for setting your fall transplants, count backward from the first fall frost in your area and add about 10 to the days to harvest from transplants. Remember that time from seed to transplant is not included in this figure When broccoli plants of most varieties are properly grown and harvested, they can yield over an extended period. Side heads develop after the large, central head is removed. Two crops per year (spring and fall) may be grown in most parts of the country. New heat tolerant varieties allow broccoli to be produced in all but the hottest parts of the season.
Planting
Plant seeds 1/4 to 1/2 inch deep, or set transplants slightly deeper than they were grown originally. Plant or thin seedlings 18 to 24 inches apart in the row and allow 36 inches between rows. Broccoli plants grow upright, often reaching a height of 2 1/2 feet. Space plants one foot apart in all directions in beds.
Maintenance
Use starter fertilizer for transplants and side-dress with nitrogen fertilizer when the plants are half grown. Provide ample soil moisture, especially as the heads develop.
Harvesting
The edible part of broccoli are compact clusters of unopened flower buds and the attached portion of stem. The green buds develop first in one large central head and later in several smaller side shoots. Cut the central head with 5 to 6 inches of stem, after the head is fully developed, but before it begins to loosen and separate and the individual flowers start to open (show bright yellow). Removing the central head stimulates the side shoots to develop for later pickings. These side shoots grow from the axils of the lower leaves. You usually can continue to harvest broccoli for several weeks.
Pests and Common Problems
Aphids — Watch for buildup of colonies of aphids on the undersides of the leaves.
Cabbage worms — Three species of cabbage worms (imported cabbage worms, cabbage loopers and diamond back moth worms) commonly attack the leaves and heads of cabbage and related cole crops. Imported cabbage worms are velvety green caterpillars. The moth is white and commonly is seen during the day hovering over plants in the garden. Cabbage loopers ("measuring worms") are smooth, light green caterpillars. The cabbage looper crawls by doubling up (to form a loop) and then moving the front of its body forward. The moth is brown and is most active at night. Diamondback worms are small, pale, green caterpillars that are pointed on both ends. The moth is gray, with diamond-shaped markings when the wings are closed. The damage caused by diamondback larvae looks like shot holes in the leaf.
The larval or worm stages of these insects cause damage by eating holes in the leaves and cabbage head. The adult moths or butterflies lay their eggs on the leaves but otherwise do not damage the plants. The worms are not easy to see because they are fairly small and blend with the cabbage leaves. Cabbage worms are quite destructive and can ruin the crop if not controlled. They are even worse in fall plantings than in spring gardens because the population has had several months to increase. About the time of the first frost in the fall, moth and caterpillar numbers finally begin to decline drastically.
