Growing Broccoli

broccoli head with tight green buds in garden

A perfect head of broccoli will be big and have lots of very tight green buds.

Broccoli is a hardy vegetable that develops best during cool seasons of the year. Two crops per year (spring and fall) are possible in most parts of the country, especially with continuous improvement in fast maturity and heat tolerance that extends the life of broccoli through all but the hottest parts of the season. It belongs to the cole crop family (Brassica oleracea), which includes cabbage, Brussels sprouts, cauliflower, collards, kale, and kohlrabi.

Soil, Planting, and Care

broccoli plants in spring cool-season garden

The crop of broccoli in this spring garden is well on its way to making heads.

Broccoli needs cool weather, full sun, water, and rich soil. Plant your broccoli where it will get least 6 hours of sun daily and has fertile, well-drained, moist soil with plenty of organic matter. Mulch will help keep the ground cool and moist. The soil pH should be between 6.0 and 7.0 for best growth and to discourage clubroot disease. To be sure about your soil pH, it is best to get the soil tested. You can buy a kit or have a soil test done through your regional Cooperative Extension office. Adjust the pH with lime, if needed, according to the test results.

For good growth, mix plenty of nitrogen-rich amendments such as cottonseed meal or composted manure into the soil. Or, you may mix in a granular organic fertilizer or a coated, timed-release vegetable food such as 14-14-14 according to label directions. Or fertilize regularly with a liquid formula such as Bonnie Herb & Vegetable Plant Food beginning when you plant. Use according to label directions; plants love the liquid feeding. If this sounds like a lot of options, it is. Gardeners develop their favorite way of doing things over time. With broccoli, the important thing is rich soil and there is more than one way to achieve that.

Plant at the spacing stated on the Bonnie label. Generally, broccoli plants should be 18 inches apart. If planted in rows, space rows 24 inches apart to give yourself enough room to walk between them, but you can plant two or three abreast in a row to minimize aisle space.

Broccoli likes steady moisture to grow fast and produce good heads. An organic mulch of compost, finely ground leaves, or finely ground bark will help keep the soil cool and moist and keep down weeds. In cold climates, it’s the opposite, you may need to plant through black plastic in early spring to help warm the soil or leave the ground without mulch so that the sun can warm it.

Water regularly, applying 1 to 1.5 inches of water per week if rain doesn’t cover it. You can measure the amount of water with a rain gauge left in the garden. If your soil is not naturally rich in nitrogen from abundant earthworms and regular additions of organic, nitrogen-rich amendments, then fertilize the plants again with a liquid fertilizer such as fish emulsion or Bonnie Herb & Vegetable Plant Food as they begin to develop new leaves and continue liquid feeding until the heads are nearly ready to harvest.

Troubleshooting

a broccoli head in the garden shouldn’t be left to stretch or flower

Don’t let your broccoli head develop to this stage. It will be mealy. If the little buds start stretching or showing yellow flower petals, cut the head, no matter how small.

Broccoli is temperature sensitive. If transplants sit exposed to cold below 40 degrees for a week or two, the chilling injury triggers heads to form way too early. On the other end of the scale, if you plant too late and the weather gets hot, you’ll get the same early blooming, so plant your broccoli on time. The ideal temperature for broccoli is between 65 and 80 degrees. For local planting dates, check with your local Cooperative Extension office. The best way to avoid pest problems is to keep your plants healthy and your garden clean. The main insect pests include cabbage loopers and imported cabbageworms, cabbage root maggots, aphids, and flea beetles. Disease problems include black leg, black rot, clubroot, and yellows. Contact your regional Cooperative Extension office for more information on pest identification and current control recommendations.

Harvest and Storage

broccoli in bowl along with lettuce, greens, and cabbage for a fall harvest

Broccoli heads are harvested along with greens, lettuce, and cabbage in the cool-season garden in fall or spring.

When you see a flower head beginning to form in the center of the plant, check its growth every day. Ideally, you harvest broccoli while the tiny buds are tightly closed. If the buds begin to swell or show yellow (the flower petals), cut the head from the stem right away, no matter how small it is, because the opening buds have a mealy texture. After cutting the main head, leave the plant to grow bite-sized side shoots in the axils of the leaves. Don’t be disappointed if your broccoli head is smaller that those in the grocery store; they are usually grown in a friendly climate and with lots of pampering. In areas where spring heats up fast, broccoli heads are often better in fall than in spring, so try again for a bigger head later. Plant in late summer. Heads keep for about a week in the fridge. Enjoy fresh heads and shoot in Healthy Broccoli Salad or Broccoli With Sesame Seeds.

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FAQs

Can broccoli be grown in the spring and the fall?

Generally, yes, depending upon the variety, the region, and the time planted. Broccoli does best when temperatures remain between 40 degrees and 70 degrees F. It needs to mature during cool periods, so it does well in most areas if planted in late summer to mature in fall. In spring, broccoli is planted early enough to mature during cool weather. Temperatures below 25 degrees F can damage or kill broccoli.

How will I know when my broccoli is ready to harvest?

Generally, you should harvest broccoli when individual buds of the broccoli head are pin-head size, dark green, and tightly closed. If yellow petals begin showing, the head is past its peak quality. After growing a certain variety for several seasons, you will soon know the potential size for heads of that variety. The size of the head depends on location, variety, season, and fertilization. Most homegrown heads are three to six inches in diameter.

Can I grow broccoli in a container?

Yes, use a container 5 gallons or larger, or at least 18 inches in diameter.

After you plant broccoli, do you have to top the plants?

No, that would remove the central head and you won’t get the harvest that you expect. However, you would get small side shoots.

My broccoli foliage is developing yellow spots on the upper side with a downy growth underneath. What does this mean?

This is downy mildew, a disease caused by an airborne fungus. Some varieties of broccoli are resistant to this. Foliar sprays of chlorothalonil (Daconil¨) can be used to control this problem. Begin applications at the first sign of the disease and repeat according to label directions.

How can I control worms that get in my broccoli heads?

These are probably loopers or imported cabbageworms that can be controlled with a product containing Bacillus thuringiensis (Bt) such as Dipel¨, a biological-type insecticide. This must be eaten by the worm and is activated in the worm’s alkaline gut. The worm then dies slowly from terminal constipation. This takes two to three days, which means the worms are not killed immediately.

My broccoli produced small yellow flowers shortly after I planted it and the heads were tiny. What caused this?

Hot weather is the culprit. The plant is going to seed. Broccoli flowers quickly in temperatures much above 80 degrees. Be sure that you are planting at the right time. Next time, you should cut off the broccoli heads before they form flowers, no matter how small they are.

What causes broccoli heads to become discolored and slightly slimy?

Under certain environmental conditions, such as high temperatures during the initiation of the head, discoloration occurs. This has been observed on some of the hybrid varieties. Planting at the correct time and providing good cultural care usually avoids the problem.

On some of my plants, the stem has a hole that retains water and causes rotting after I remove the main head. What can I do?

The hole in the stem cannot be corrected now. It is caused by a boron deficiency that is corrected by adding boron to the soil for next year. The rate is one-half pound per 1,000 square feet of a boron product such as Twenty Mule Team Borax. Dissolve it in two gallons of water and spray it evenly over the ground. DO NOT OVER APPLY. Boron toxicity occurs if too much is added, so use only what is required. Don’t be tempted to think that a little extra is better.

Is it normal for seconday sprouts to be smaller or should we fertilize?

The center head produced by broccoli is always the largest. The secondary heads are about the size of a silver dollar. Side-dressing with fertilizer can increase yields and size of these shoots. Although small, they are just as tasty as the large center head.

A few of my broccoli plants did not produce heads, but look healthy. What is wrong?

If the growing tip of a broccoli plant is injured, it may not head. This is called blindness. The transplant could have been injured in transit, while planting, or by an insect in the garden.