Growing Broccoli from Seed to Harvest

Today on the Green Pinky, we’ll teach how to grow a huge head of healthy, green broccoli with our in-depth guide.

Broccoli (Brassica oleracea) is a mustard family member along with cauliflower, cabbage, kale, and Brussels sprouts. The plant grows upright to approximately 3 feet tall, with a main stalk and broad, thick leaves. A main head forms at the top of the stalk, with side shoots growing off of it.

The following will walk you through all the steps of broccoli growing — from sowing seeds, how to plant transplants, and determining when to harvest.

Soil Prep

Broccoli has a relatively short growing season, so it’s necessary to make sure the garden soil is well-prepped before planting. Fertile, well-drained soil will allow for optimal, healthy growth.

  • It prefers slightly acidic soil, with a pH between 6.0 and 7.0. Check the soil pH before the season and amend it if too far out of the preferred range.
  • Work the soil to a depth of 12 inches, breaking up any large clods to loosen the ground.
  • To increase the soil fertility and improve drainage, work in 2 to 4 inches of finished compost or manure.

Planting Seeds

Broccoli is a cool-season vegetable. It needs cool weather to germinate and grow, so it matures before air temperatures are consistently over 75℉. When temperatures are higher than this, their low heat tolerance causes the plant to bolt in an attempt to set seeds rather than developing heads.

When started inside and grown from transplants, it is ready to harvest in 55 to 85 days; it takes 70 to 100 days when growing from seed.

Timing

For a summer harvest, plant in late winter or early spring. If you want to grow for a fall harvest, start it later in the growing season, so that the heads develop in the cool weather of fall.

Spring Plantings

Start seeds indoors in early spring, approximately 6 to 8 weeks before the last frost. When seedlings have 4 to 5 true leaves, harden them off for a couple of days to acclimate to the weather and plant seedlings outside. On average, this falls about two to three weeks before the frost-free date.

Fall Planting

For a fall harvest, direct sow seeds in mid to late summer, giving plants adequate time to grow and mature before the first fall frost Aim to plant seeds approximately ten weeks before the first typical frost fall in your area.

Spacing

Direct sowing

Plant seeds in the soil about ½ inch deep and 3 inches apart, with 3 feet between the rows. Thin seedlings to 18 to 24 inches apart when they reach two to three inches tall, about 4 to 6 weeks old.

Transplanting seedlings

When transplanting seedlings, space the seedlings 18 to 24 inches apart within the rows, and space rows 3 feet apart. Plant leggy transplants or those with crooked stems a little deeper in the soil, burying them up to their first leaves, so they don’t grow top-heavy.

Care Guide

Overall, it is pretty simple to grow broccoli. They aren’t very fussy and don’t require much attention from you. To reap the best harvest possible, though, give them the following care throughout the growing season.

Sunlight

Broccoli needs a garden spot designated as a full sun location, where it receives a minimum of six to eight hours of direct sunlight daily. If your garden does not get full sun, then they will tolerate partial shade but be aware it affects their growth—a lack of adequate sunlight results in thin, leggy plants that develop smaller, subpar heads.

Watering

Water regularly to keep the soil moist, especially as daytime temperatures climb, without waterlogging the roots. Aim to give plants 1 – 1 ½” of water every week, decreasing slightly as plants get close to maturity.

Fertilizing

Approximately three weeks after transplanting seedlings into the garden, apply a low-nitrogen fertilizer. High nitrogen levels result in too much leaf growth. Broccoli needs higher levels of potassium and phosphorus for flower head and bud development.

Weeding

Their root systems is very shallow and easily disturbed by mechanical weeding, resulting in growth and yield reduction. It’s better instead to prevent weeds by mulching the garden bed around the plants.

Pest and Disease Management

Insect pests include aphids, cabbage worms, cabbage loopers, and whiteflies. Common diseases are clubroot, downy mildew, and white rust. Scout regularly for problems, treating the broccoli as soon as an infestation is identified. Insects will quickly decimate an entire plant if left untreated.

Harvesting

Knowing when to harvest is a bit tricky, but it is much easier when you have a basic understanding of their physiology.

When Should You Harvest?

The edible part of the plant is the flower heads before the buds open. Harvest the central head on the plant when it’s fully developed, but before the individual flower buds open, displaying small yellow flowers.

When ready to harvest, the main head is tight and compact, and the florets a deep green color. Once the yellow flowers start to appear, harvest the heads immediately.

How Do You Harvest?

Harvesting is best done in the cool morning hours when temperatures are lower for high-quality heads.

Using a sharp knife, remove the main head, taking about 6 inches of the stem. Leave the rest of the broccoli growing in the garden. After the first head is harvested, the plant sends hormones that serve as internal messages to encourage the development of side shoots.

These side shoots are smaller than the central head, but they develop into heads, allowing you to continue harvesting them for a more extended period.

Growing Tips

  • Rotate planting areas in your garden, so you do not plant broccoli in an area that has grown any Brassicaceae (cabbage family) crops over the previous four years.
  • Avoid overhead watering – water in the heads promotes rot.
  • Row spacing closer than 3 feet yields smaller main heads but a greater number of secondary heads from side shoots.
  • Using row covers helps to minimize pest problems such as insects, rabbits, and deer.
  • Shade cloth is useful to cover plants and keep them from bolting in hot weather.
  • Maintain the same active watering schedule after harvesting the main head to promote the growth of side shoots.
  • Prevent boron deficiency (hollow stems, poor discolored bud formation) by sprinkling borax on the garden soil around plants.

Companion Plants

Broccoli grows well with various garden plants. It’s important to space them properly though because they grow both tall and wide and will overshadow and outcompete smaller neighbors.

Common companion plants include beets, radishes, celery, onions, shallots, potatoes, lettuce, spinach, and herbs (chamomile, rosemary, dill, mint, thyme).

  • Herbs deter pests due to their aroma.
  • Oxalic acid in rhubarb leaves acts as a natural pest repellent.
  • Celery and chamomile are thought to improve the taste of broccoli.
  • Lettuce and spinach grow well in the shade of tall broccoli plants since they are cool-season vegetables.

Avoid planting near any other cruciferous vegetables or heavy feeders such as beans, strawberries, corn, squash peppers, or tomatoes.

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Happy Planting!

About the author: Carley Miller is a horticultural expert at TheGreenPinky. She previously owned a landscaping business for 25 years and worked at a local garden center for 10 years.

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