Broccoli, Brassica oleracea, isn't difficult to grow when you understand how it grows. It's different from other crops partly because broccoli is temperature sensitive throughout its growing stages. It also takes careful watching to harvest at the right time.
Broccoli produces flowers like many ornamentals that send up a main stalk with branching floral spikes or stems. Once the small yellow flowers bloom the vegetable becomes tough and bitter, so, you want to harvest broccoli while it's still in the flower bud stage.
Considered one of the cole crops, broccoli is grown as an early spring or autumn annual depending on the growing zone. Whether you're starting with seed or transplants, know when your variety matures and keep a calendar handy. From seeds to harvest, providing the right conditions at the right time makes all the difference in successfully growing this highly valued, nutritional vegetable.
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Germination occurs when a seed breaks through its covering and a green shoot emerges from the soil. Broccoli seeds germinate quickly in five to ten days with warm temperatures of 80 degrees Fahrenheit. Soaking seeds in hot water for 24 hours prior to sowing can aid germination.
If you're starting from seed, choose a variety that matures before temperatures in your growing zone reach 75 degrees Fahrenheit. Different varieties mature from 50 to 70 days.
Broccoli does well as a spring planting in northern zones with cooler summer temperatures. Start seeds indoors six to eight weeks before final frost. Southern growers have better success planting broccoli for an autumn harvest. In zones 5 through 7, typical weather patterns are the deciding factor. When spring temperatures fluctuate or rise quickly broccoli can fail to head up or heads may bolt. Starting seeds either in flats or in the ground from mid to late summer may add up to better results.
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During broccoli's seedling stage, the structure for nutrient uptake and photosynthesis begins to develop. A root system forms and new true leaves emerge from the stem. Cooler temperatures of 60 to 65 degrees Fahrenheit are needed, so continue to grow seedlings indoors for two to three weeks or until they have several sets of leaves before transplanting into the garden.
Plan to set out spring-grown broccoli seedlings one to two weeks before final frost. Allow time for hardening off. For autumn harvest, transplant seed starts or purchased seedlings when daily temperatures average between 65 and 75 degrees Fahrenheit.
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The vegetative stage signals the start of the broccoli plant's most active growth. Over about the next four weeks, it can grow to 3 to 4 feet wide and tall with large leaves.
The main stem begins to develop a small button-size head of small green flower buds that remain unopened. This first flower bud is often referred to as the crown. Branches start to emerge from the main stem which are, essentially, flower stems that also will produce green buds as the plant matures into the flowering stage.
The ideal temperature for this life cycle phase is 65 to 75 degrees Fahrenheit. Adequate light, soil moisture and nutrition are important because it takes a lot of energy for a plant to produce flowers. Apply fertilizer higher in phosphorous and potassium. Too much nitrogen can cause failure to form a head. Row covers protect against caterpillars and other prevalent insect pests at this stage.
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Harvest (Flowering) Stage
When broccoli is reaching maturity, the crown or center stalk head grows wider with multiple green buds. Stems branching off the main stalk begin to produce green buds tightly packed around the crown. Now is the time to keep a close eye on the plant for signs flowers are preparing to open. Flowering or bolting, in the case of broccoli, can occur when average daily temperatures top 75 degrees Fahrenheit. Revisit your seed packet and calendar for the "days to maturity" for your broccoli variety.
A good time to harvest is when the crown topping the main stem is 2 1/2 to 3 inches across. Combined with branches, the entire head may be 6 inches across or wider.
Watch for flowerheads to start to separate between the stems and crown. The green buds swell and begin to take on a yellow color. Once the process begins it only takes several days for the buds to bloom and turn your broccoli crop into a grainy, bitter vegetable.
How long does it take broccoli to grow?
Different varieties mature at different times but usually somewhere between 50 and 75 days from germination.
How long does it take for broccoli to grow a head?
Several factors influence heading up, including temperature, nutrition, and variety planted. Watch for the first button-size flower bud to appear on the main stalk anywhere from three to five weeks after planting out. It will continue to get bigger until harvest, however when temperatures exceed 75 degrees watch for signs of bolting.
How many heads of broccoli do you get from one plant?
A head of broccoli is considered the main stem and branches. Each plant produces just one head. Once the large central head is harvested, florets continue to emerge from leafstalks. Much smaller, these also are edible.