Broccoli (Brassica oleracea var. italica) is a must-grow vegetable for every cool-climate gardener. I find that it’s easy to grow — assuming you know the basics — and is extremely versatile in the kitchen. But growing broccoli at home does require a bit of patience!
If you’re new to growing broccoli in your vegetable garden, I recommend starting your journey by learning about the broccoli plant growth stages and what to expect throughout its biennial life cycle. In this article, I’ll cover exactly that.
Conditions for Growing Broccoli
Broccoli thrives in cool weather, so you’ll want to plant this vegetable in either early spring or fall to avoid the stress of summer heat. Extremely hot or rapidly changing temperatures can impact broccoli growth and trigger a phenomenon known as bolting.
Broccoli is one vegetable that tolerates sowing several weeks before the year’s last frost date. However, starting broccoli seeds indoors is a great way to make the most of your available growing season. In some climates, this is the only way to cultivate mature broccoli before the heat of summer takes its toll.
Like other brassicas (e.g., cabbage, Brussels sprouts, cauliflower, etc.), broccoli grows in full sun. According to the University of Maryland, broccoli plants should receive at least 6 hours of direct sunlight per day but prefer 8 to 10 hours.
Broccoli grows best in slightly acidic soil with a pH of 6.0 to 7.0. I recommend amending the soil with aged compost or a similar organic fertilizer prior to the start of the season to increase nutrient content. Alternatively, you can apply a low-nitrogen fertilizer a few weeks after establishing broccoli in your beds.
Adequate moisture is crucial to growing high-quality broccoli. According to Utah State University, broccoli needs 1 to 2 inches of water per week via either natural rainfall or irrigation. Be sure to water the soil deeply and, if needed, use a mulch to maintain consistent moisture levels. Keep broccoli heads dry to reduce the risk of rot.
Growth Stages Of Broccoli
Broccoli can be an annual or a biennial plant. Most home gardeners grow broccoli as an annual, meaning that it completes its entire life cycle in a single season. To grow broccoli as a biennial, it must be planted in the fall and overwintered before completing its life cycle the following spring.
Most broccoli cultivars require about 100 days from germination (or 50 to 65 days from transplanting) to reach harvest. After cutting the main stalk, you can continue harvesting new growth as long as the weather remains favorable.
Note that different cultivars mature at varying rates and perform best during specific parts of the season. According to Clemson University, broccoli is typically categorized as full-, early-, mid-, or late-season. You can use these labels to select cultivars best suited to your garden — for example, an early-season cultivar like ‘Packman’ can be planted and will mature sooner than a mid- or late-season cultivar.
1. Seed Germination
In the spring, broccoli seeds can be direct-sown in the garden as soon as the soil is workable (2 to 3 weeks before the last frost date) or started indoors in seed trays 6 to 8 weeks before the area’s last frost date. To grow a fall crop, start seeds indoors in July or early August.
Broccoli seeds can technically germinate in temperatures as low as 40°F. In my experience, however, germination rates will be significantly better at temperatures between 50 and 85°F. Average household temperatures are ideal for indoor germination.
Whether sowing seeds indoors or directly in garden beds, the soil must stay consistently moist to trigger germination. The planted seeds need exposure to 8 hours of bright sunlight on average per day. You can expect to see sprouts emerge 5 to 10 days after broccoli seeds are planted.
You can purchase broccoli seeds from nearly every home and garden store, with many grocery stores offering a limited selection during the growing season. For more specialized cultivars and heirloom varieties, I recommend ordering through your favorite seed catalog or online retailer.
The first two leaves of a broccoli sprout are called cotyledons. These aren’t true leaves and look different from the plant’s mature foliage.
By the time your broccoli seedlings are 28 to 42 days old, they should have several ‘true’ adult leaves. Seedlings that have at least 4 adult leaves are ready for transplanting.
I recommend thinning out your broccoli seedlings when they reach about 3 inches tall. If starting seeds indoors, pinch off all but the strongest sprout in each cell. Outdoor seedlings should be thinned out to be at least 12 inches apart. Do not pull out extra seedlings as you might damage the roots of nearby sprouts.
In the spring, the best time to transplant indoor seedlings is when the temperature reaches at least 65°F. Fall broccoli should be transplanted when the daily temperature drops below 75°F.
While broccoli is relatively cold-hardy, seedlings need to be hardened off before transplanting to the garden. Do this by placing your broccoli seedlings outdoors for a few hours, increasing the duration a bit each day — start this practice about 2 weeks before transplanting.
3. Vegetative Growth
When it comes to growing broccoli in the garden, vegetative growth is the name of the game. All parts of a broccoli plant are edible, including the lower leaves.
Cultivars like ‘Calabrese’ — i.e., the type of broccoli commonly found in most grocery stores — produce large central stalks and heads. However, there are also many broccolis that produce several smaller heads that are equally as rewarding to grow!
The average broccoli stalk will grow to 2 to 3 feet in height over the course of its growing season. Your broccoli will likely reach its full size 50 to 65 days after transplanting or about 100 days after the seeds germinate in normal outdoor conditions.
Broccoli plants can become surprisingly big, so be sure to measure your garden beds ahead of time. Overcrowded broccoli tends to produce smaller stalks and heads than counterparts that receive plenty of elbow room.
It is during the vegetation stage that caterpillars and whitefly can become a serious problem. In some areas, it may be necessary to cover plants with netting to prevent butterflies from laying their eggs on the underside of leaves.
Companion planting with fragrant herbs such as rosemary, mint, dill or thyme will deter pest insects such as whitefly, beetles, and aphids.
The flowering stage is very important when growing edible broccoli but probably not in the way you think. Broccoli heads are made up of hundreds of tiny florets — immature flower buds. So the perfect time to harvest broccoli is technically halfway through the flowering process.
If left unharvested, these florets will soon open up to reveal small yellow flowers. Broccoli flowers are also edible and also attract common garden pollinators.
Bolting, or premature flowering is the downfall of many prospective broccoli growers. Because broccoli is eaten when the flowers are immature, bolting can essentially ruin a harvest overnight.
There are many factors that contribute to bolting but the temperature is the most common. Soil that gets too warm (above 80°F) may trick broccoli plants into flowering early. Using mulch, providing adequate moisture, and shading the plants during the hottest part of the day can prevent bolting in some cases.
Other environmental factors like stress, disease, and pest infestation can trigger bolting. This is explained by the fact that the broccoli plant senses danger and wants to reproduce as quickly as possible in case it dies.
Pollination is not required to produce edible broccoli florets. However, it is necessary if you want to collect and save seeds for future crops.
Bees and other flying insects are significant broccoli pollinators. Hand-pollinating is also possible.
In my experience, most types of broccoli are not self-fertile. This means that pollen from a separate plant is needed to create viable seeds. If you plan to collect broccoli seeds from your garden, you need at least 2 compatible plants.
Note that cole crops — i.e., varieties of Brassica oleracea — are easily cross-pollinated. Broccoli plants may cross-pollinate with nearby Brussels sprouts, cauliflower, or cabbage to create unusable seeds. Successful seed production for future growing seasons may require isolating your broccoli plants.
Broccoli Plant Growth Timeline – Timelapse Video
This short video shows the various growth stages of broccoli from seed to mature plant. This plant is grown under artificial grow light on 24hrs of daylight which reduces the growth time significantly.
When To Harvest Broccoli
Deciding when to harvest broccoli is quite easy. On average, broccoli that is ready to harvest will have a central stalk 3 to 6 inches in diameter and a head 4 to 7 inches wide. There are also several visual cues to watch for as your cultivar’s harvest date grows near:
- A large, firm head
- Deep green florets
- Florets that are the size of a matchhead
Generally speaking, it’s better to harvest broccoli slightly early than to wait too long. If you notice any hints of yellow within your broccoli’s florets, it means that the flowers are starting to open.
Your broccoli plants may continue growing after the first harvest. You can continue harvesting new growth as it appears, keeping in mind that additional heads are unlikely to grow as large as the first one.
When growing broccoli in the fall, keep a close eye on the upcoming forecast for signs of frost. According to South Dakota State University, broccoli can tolerate mild freezes without issue. However, you want to ensure plenty of time for harvest before your area encounters excessively cold temperatures.
FAQ Broccoli Plant Growth Stages
What Are The Little Worms In Broccoli?
Broccoli worms like to feed on a variety of brassica vegetables, including broccoli. There are several small, green caterpillars commonly found on broccoli, including the cabbage worm, cabbage looper, and diamondback worm. You can control these pests with a natural insecticide containing Bacillus thuringiensis.
- The University of Maryland Sun requirements for broccoli
- Utah State University Watering requirements for broccoli
- Clemson University Broccoli growth rates South Dakota State University Broccoli freeze tolerance
Ben's horticultural interest grew when graduating from Hertfordshire University in 1997. Having contributed to numerous publications including Better Homes & Gardens, Garden Design Magazine, and The English Garden. He is also the author of Propagating Houseplants Made Easy.