Broccoli is a member of the plant family known as Brassicas. These vegetables grow best during cool seasons and two crops can be grown in your garden in spring and fall. Broccoli and other brassica vegetables typically do not tolerate high heat and humidity.
The head from the center of the broccoli plant is what you’re most familiar with. But the broccoli leaves can also be eaten and used as you would kale or collard greens.
What are Brassicas?
Broccoli is a member of the mustard family of plants known as Brassicaceae. Brassicas are also known as cruciferous vegetables or cole crops. Also in this family of plants are arugula, brussels sprouts, bittercress, kale, bok choy, cabbage, cauliflower, collard, rutabaga, turnip, horseradish, radish, watercress, and others. Most varieties of brassicas grow best in cool weather. That’s why they’re some of the first crops to be planted in the vegetable garden in spring and many gardeners plant them again in late summer for a fall harvest. Brassicas don’t like fluctuating temperatures or high heat – you’ll notice after a few seasons growing broccoli, cauliflower, and brussels sprouts that they do best when springs and summers are cooler than average.
Mom was right – eat your vegetables
Brassicas are a fantastic nutritional choice, as these vegetables contain a wealth of phytochemicals. According to research from the National Institutes of Health, Brassicas “prevent oxidative stress, induce detoxification enzymes, stimulate the immune system, decrease the risk of cancers, inhibit malignant transformation and carcinogenic mutations, as well as, reduce the proliferation of cancer cells.” That’s quite a nutritional benefit. If this family of vegetables is not regularly in your diet, you’re missing out on substantial health benefits.
Brassicas are full of vitamins C and E, carotenoids and antioxidant enzymes such as catalase, and they contain polyphenols and sulfur-organic compounds that have antimutagenic action (reducing mutation in cells). They are also thought to inhibit DNA methylation and cancer development.
Types of broccoli
There are four types of broccoli: heading (most common), Romanesco, sprouting, and raab.
Heading type of broccoli
The heading type of broccoli forms a large central head (this is the type most commonly seen on grocery shelves). Mature heads measure 3 to 8 inches across, depending on the variety. After the central head is cut on spring-planted broccoli, smaller heads develop on the plant, which can also be eaten.
Romanesco broccoli
Romanesco broccoli produces dramatic, spiraling heads.
Sprouting broccoli
Sprouting broccoli, aka Italian broccoli, forms many florets or small heads, but this type does not produce a solid head.
Broccoli raab
Broccoli raab, aka turnip broccoli, is not actually broccoli – it’s a type of turnip.
Preparing garden soil for broccoli
Broccoli requires fertile soil with a pH between 6.0 and 7.0 As with other brassicas, broccoli relies mostly on potassium and phosphorous for its growth. Most soils in North America have these elements in sufficient quantities, so fertilizer only needs to be added if a soil test indicates a need for potassium or phosphorus. However, adding compost or composted manure to garden soil is highly recommended before planting to increase fertility, build organic matter, and improve drainage. If you grow broccoli on sandy soil, irrigation will be important for optimum plant growth and head and side shoot development.
Don’t plant broccoli in the same garden bed 2 years in a row, or in the same bed where brassicas were planted the previous year. Broccoli and all brassicas are subject to the same nutrient deficiencies, diseases, and pests, so practice crop rotation to avoid flea beetles, imported cabbage worm, cabbage looper, diamond back moth, cabbage maggots, black leg, clubroot, black rot, and Alternaria leaf spot.
When to plant broccoli
The ideal air temperature for growing broccoli is between 65 to 80° F. That means you should plant broccoli seedlings in spring after the threat of frost has passed and soil temperatures have reached 50 degrees F.
Broccoli and brassicas, in general, don’t like high heat or widely fluctuating temps. When the plants are young, very warm or hot periods accompanied by inadequate moisture can cause the broccoli heads to become malformed, pale, or uneven. If you have a very hot spring you can end up with heads that don’t form or that are very small and bitter.
On the other hand, planting broccoli seedlings too early can result in “buttoning up” – heads become very small when exposed to a string of consecutive nights below 50 degrees F. Timing and temperature are critical for successful broccoli, so keep an eye on the weather.
Broccoli seeds can be started indoors over winter and seedlings can be planted 4-6 weeks before your last frost. Seeds can be planted again in late July for a fall harvest. Sprouting broccoli and raab broccoli seed can be sown in the garden in spring. But it is generally not recommended to start heading type broccoli from seed in your garden in spring as there won’t be enough time for heads to develop before the summer heat arrives, and spring soil is typically too cold for broccoli seeds to germinate.
Choose a location with full sun. Plant broccoli seedlings or seeds about 10 inches apart, as the mature plants need plenty of space for proper head development. If planted too close together the heads will be very small.
For a fall broccoli harvest
Broccoli sweetens when it’s exposed to cold temperatures and light frosts. But if you plant too late in summer and fall comes early, you may have no heads at all. Generally, you want to start seeds indoors in mid-July and then transplant outdoors when the weather cools. Seeds can also be sown outdoors in mid-July, but watch out for heat damage to seedlings. For best success, always choose a variety appropriate for your climate.
Fertilizing broccoli
Use a slow-release organic fertilizer that is low in nitrogen – giving too much nitrogen to young plants can result in hollow stems. Gently work the fertilizer beneath the soil to avoid the loss of nitrogen to air, being careful not to disturb the shallow roots. Add 2″ of compost around seedlings after planting to provide organic material and nutrition. Side dress the plants with an additional 2″ of compost one month after planting seedlings. See our post on planning for a fall vegetable harvest.
Watering broccoli
Broccoli needs substantial water for plant and head development, so provide 1 to 1.5 inches per week in the absence of rainfall. If they’re deprived of water, the heads may not form correctly and will taste bitter (they’re definitely still edible, but won’t have the sweetness that’s ideal).
When to harvest broccoli
Depending on the variety, broccoli grown from seed will be ready to harvest in 100 to 150 days, and transplants will be ready to harvest in 55 to 80 days. It’s time to harvest broccoli when the center crown is full of tiny, green, tightly-packed buds. If the tiny buds of the head begin to swell or turn yellow, harvest it right away regardless of size, as it’s going to flower and will begin to taste mealy if left in the ground longer.
Harvest the broccoli head from the stalk and leave the rest of the plant in the ground. New side shoots that look like small heads of broccoli will form which can be harvested when ready.
We garden in Pennsylvania, United States, zone 6B. Much of the info we share is based on gardening in our temperate area. But many of the flowers, vegetables, and fruit we write about can be grown in soil other than ours (clay) and significantly different weather conditions and elevations. You might need to choose specific varieties for your region, modify your garden, add soil amendments, or adjust the soil pH to match our results. Please check your local university extension website for specifics for your area.
I love the broccoli from the garden but what do I do about the green little worms that get in it?
Donna: Diatomaceous Earth is an organic pesticide that will help very much with all types of insects. Read about it here.
Hello Todd, I really enjoyed reading your article about how to grow broccoli, I found it very helpful. Thank you, Richard