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Broccoli

When to Plant

  • Broccoli is cool-season crop, so it should be started in late winter or early spring (depending on your climate) for an early summer crop, or in mid- to late summer for a fall crop. High temperatures will affect development of the broccoli head (the harvestable part), so the goal is to get broccoli to mature before or after high temperatures are expected.

  • Broccoli seeds are capable of germinating in soil temperatures as low as 40°F (4°C), but warmer soil is preferred and will greatly speed up development.

  • For spring plantings, broccoli may be started indoors or outdoors a few weeks ahead of your last spring frost date. Consult our Planting Calendar to see recommended dates for your area. Generally speaking:

    • Start seeds indoors 6 to 8 weeks before your last frost date.

    • Sow seeds outdoors 2 to 3 weeks before your last frost date, or as soon as the soil can be worked in the spring.

  • For fall plantings (best in warm climates), sow seeds outdoors 85 to 100 days before the first fall frost, when soil and ambient temperatures are high.

Choosing a Planting Site

  • Broccoli requires a site with exposure to full sun (6 to 8 hours per day). Lack of sunlight may produce thin, leggy plants and subpar heads.

  • Plant in a bed of moist, fertile soil that drains well.

  • Soil pH should be slightly acidic, between 6.0 and 7.0.

  • To increase fertility before you plant, in early spring, work in 2 to 4 inches of rich compost or a thin layer of manure. (Learn more about soil amendments and preparing soil for planting.)

How to Plant

  • If starting seeds outdoors, sow seeds 1/2-inch deep and 3 inches apart.

  • Once seedlings reach a height of 2 to 3 inches, thin them so that plants are 12 to 20 inches apart.

  • If you started seeds indoors, plant transplants that are 4 to 6 weeks old (and have 4 or 5 leaves) outdoors, 12 to 20 inches apart, in holes slightly deeper than their container depth. 

  • Space rows of broccoli 3 feet apart. (Closer spacing yields smaller main heads, but more secondary heads.)

  • Water well at the time of planting.

How to Grow

  • Plants thrive outdoors in 65°F to 70°F (18° to 21°C) conditions.

  • Fertilize broccoli three weeks after transplanting seedlings into the garden. Use a low-nitrogen fertilizer.

  • Thin when young plants reach 2 to 3 inches tall. Plants should be between 12 and 20 inches apart.

  • Provide consistent soil moisture with regular watering, especially in drought conditions. Water at least 1 to 1 1/2 inches per week.

  • Do not get developing broccoli heads wet when watering, as it can encourage rot.

  • Roots are very shallow, so try not to disturb the plants. Suffocate weeds with mulch.

  • Mulching around plants will also help to keep soil temperatures down.

  • Use row covers to minimize pests.

  • To promote the growth of a second head after the first has been harvested, maintain an active feeding and watering schedule.

Pests/Diseases

  • Aphids: Curling leaves may mean that the plant's sap is being sucked by insects. Apply soapy water to all sides of leaves whenever you see aphids.

  • Cabbage loopers: Small holes on the leaves between the veins mean small green caterpillars are present. Look at the undersides of the leaves. Hand pick if the problem is small or control with Bacillus thuringiensis, a natural, bacterial pesticide. Use a floating row cover just after planting through harvest to prevent caterpillars.

  • Cabbage root maggots

  • Cabbageworms and other worm pests: Treat same as loopers.

  • Clubroot: Quickly wilting plants may be due to this fungus in the soil. The entire plant, including all roots and root tendrils, must be gently dug up and removed. If the roots are gnarled and misshapen, then clubroot is the problem. Act quickly to remove the plants so that the fungus doesn't continue to live in the soil. Do not compost the plants. Raise the pH of your soil to above 7.2. You may need to sterilize your soil, too.

  • Downy Mildew: Yellow patches on leaves are usually caused by moist weather. Keep leaves as dry as possible with good air circulation. Buy resistant varieties.

  • White rust

  • Whiteflies

  • Nitrogen deficiency: If the bottom leaves turn yellow and the problem continues toward the top of the plant, the plants need a high nitrogen (but low phosphorus) fertilizer or blood meal. Blood meal is a quick nitrogen fix for yellowing leaves.

How to Harvest

  • Harvest broccoli in the morning, when the buds of the head are firm and tight, just before the heads flower.

  • If you do see yellow petals, harvest immediately, as the quality will decrease rapidly.

  • Cut heads from the plant, taking at least 6 inches of stem. Make a slanted cut on the stalk to allow water to slide away. (Water can pool and rot the center of a flat-cut stalk, runing the secondary heads.)

  • Most varieties have side-shoots that will continue to develop after the main head is harvested. You can harvest from one plant for many weeks, in some cases, from spring to fall, if your summer isn’t too hot.