Summary of Broccoli Growing Guide
Growing Broccoli outdoors –if done, rationally, and on a scalable basis- can be a good source of income. In a few words, Broccoli is a biennial plant but we grow it as an annual. Broccoli is grown for its flower heads, which people consume when they are still immature.
Most commercial Broccoli growers start the crop from seeds (hybrid seeds in most cases) in an indoor protected environment. As they wait for the young seedlings to grow and be ready for transplanting (usually 30 days), they prepare the field. They till the land, they remove any previous cultivation remains and weeds and integrate into the soil the basal fertilization combined with well-digested manure. They also design and build a drip irrigation system.
When they are ready for transplanting, they make small holes in the soil, where they plant the seedlings. Fertilization, Drip Irrigation, and Weed Management are applied in most cases. Most commercial broccoli varieties can be harvested 60-90 days after transplanting. Time from Planting to Harvesting depends on the variety, climate conditions, and the age of the seedlings. Harvesting can be made through hand scissors or knives and is usually performed in multiple sessions, in case growers have made continuous plantings. Contrary to cauliflower, each broccoli plant can yield more than one head. After harvesting, Broccoli growers plow and destroy the remaining of the crop. They may also rotate the crop (with plants that do not belong in Brassicaceae family), to control diseases and prevent soil from depleting.
The restrictive factor when growing Broccoli is always the climate. The plant prefers mild temperatures to thrive and form flower-heads, which is our primary goal. It is sensitive to frost, and it starts to have problems in temperatures under 0°C (32°F). Additionally, high temperatures also cause problems, especially to heads that begin to bloom. As optimum temperatures, we consider average temperatures of 10-20°C (50-68 ℉); however, some hybrid varieties can tolerate up to 30°C (86 °F) for a short period. If we want to achieve an average yield, our broccoli plants should mature and give heads either before or after hot weather and intense heat arrive.
First of all, it is crucial to decide the growing method as well as the varieties of broccoli that thrive in our area. There are four main divisions of Broccoli. Each of the four main broccoli types has different characteristics and climate preferences and are:
How to Grow Broccoli from Seed – How to make Broccoli seedlings
In general, commercial broccoli farmers do not prefer to sow broccoli seeds directly in the field for various reasons. First of all, broccoli seeds are tiny, and broadcast seeding will result in uneven sowing. Besides, when little broccoli plants appear on the ground, they often become a feed for snails and other soil pests.
However, if you insist on sowing your broccoli seeds directly outdoors, the most suitable period to do it is probably either in early spring or in autumn. If you plant them in spring, they will be ready for harvesting during summer. On the other hand, autumn planting will give your broccolis ready for harvesting during winter. After preparing the field, farmers create rows at 70-80cm (27.5-31.5inches) distance one from another. Then, they dig holes at distances of 46cm (18 inches) on the rows. Subsequently, you may sow 3-4 seeds in every hole at 1cm (0.4inch) depth and gently cover with soil. You can irrigate immediately after seeding.
Broccoli germinates best at a temperature of 20-25 °C (68-77 °F). The seed needs to have optimum moisture levels to sprout. Excessive irrigation can be harmful. Some producers water every other day during this stage. Under optimum conditions, broccoli seeds germinate in 6-10 days. After germination, you will most probably need to thin the plants. In case more than one seed has sprouted, you will have to remove all but the healthiest one from every sowing position. Keep in mind that every grammar contains 300-350 broccoli seeds. On average, you will need 1kg (2.2 pounds) of seed per hectare for direct seeding. Keep also in mind that 1 hectare = 2,47 acres = 10.000 square meters.
However, most commercial broccoli growers start the crop from seeds (hybrids) in an indoor protected environment. Growers sow broccoli seeds in seedbeds under controlled temperature of 20-30°C (68-86°F) and then transplant them into their final positions. They sow 2-3 seeds in every pot at 1cm (0.4 inches) depth and gently cover with soil. They use about 300-400gr of seeds for every hectare of outdoor plantation. They often use turf as a substrate for optimum aeration. It is crucial to maintain the substrate moist but not wet until the seed sprouts. Seeds will approximately germinate in 6-10 days, and the seedlings will be ready for transplanting after 25-40 days (4-6 weeks). By then, they will have developed 3-5 real leaves, and they will have an average height of 12 cm (4.7 inches).
Broccoli Climate and Soil Requirements- Where can Broccoli grow?
Broccoli is natively a cool-season vegetable. As optimum temperatures for broccoli development, we consider those between 10 and 20°C (50-68°F). If the broccoli plant experiences higher temperatures during its first growth stages, it will most probably start to perform intense stem growth and will delay the formation of the flower heads. At temperatures over 20°C (68°F), the plant starts to form leafy curds. This is something we have to avoid. Temperatures over 26 °C (78.8°F) will probably cause the heads to bloom, decreasing their quality and commercial value. However, nowadays we have hybrid broccoli varieties that are genetically programmed to tolerate temperatures up to 37°C (99°F) for a short period.
Broccoli can grow in a wide variety of soils. Although it grows best in slightly acidic soils (pH 6 to 6,5), farmers are sometimes recommended to grow it in neutral to slightly alkaline soils. The reason is that in slightly alkaline pH, we may avoid the development of root cancer or (“clubroot”). The pathogen Plasmodiophora brassicae causes the clubroot. It prefers acidic soils but it can be restrained to pH above 7. The plants have middle tolerance in soil and water high salinity levels.
Broccoli Soil Preparation
The basic soil preparation starts some weeks before transplanting broccoli seedlings. Farmers plow well at that time. Plowing improves soil aeration and drainage. At the same time, farmers remove rocks and other undesirable materials from the soil.
One week before planting, many farmers apply a pre-planting fertilizer, such as well-rotted manure or synthetic commercial slow-release fertilizer, always after consulting a local licensed agronomist. Many farmers integrate manure using tractors. The next day is probably the right time to install the drip irrigation system. Following the installation, some farmers can apply soil disinfection substances. They inject them through the irrigation system, in case soil analysis has revealed soil infection problems (ask a licensed agronomist in your area).
Broccoli Planting and Plant Spacing – How many Broccoli Plants per hectare?
When it comes to planting broccoli seedlings in the field, there are two main periods to choose from. The first period begins with planting during early spring, so that broccoli will be ready for harvesting during early summer. The second period includes planting in autumn and in this case harvesting takes place during winter.
In many cases, the most suitable period to plant broccoli outdoors is during autumn. Farmers generally prefer plants aged from 3 to 5 weeks. At this point, they have developed 3-5 real leaves and have an average height of 12 cm (4.7 inches).
After all the preparation steps (plowing, basal fertilization, tillage, and installation of the irrigation system), we can proceed with transplanting. Growers label the exact points where they will place the young plants. They then dig holes and plant the seedlings. It is crucial to plant the seedlings at the same depth as they were in the nursery. Many growers prefer to plant broccolis periodically every 2-3 weeks. They do so to be able to harvest broccolis periodically and thus cover the market demands.
In most cases, growers plant broccolis in single rows. They keep 40-50 cm (16-20 inches) distance between plants on the row and 45-80 cm (18-31 inches) distance between the rows.
In most cases, farmers plant 25000-40000 plants per hectare. (1 hectare = 2,47 acres = 10.000 square meters). There are cases in which the plant population of broccolis in a hectare can be 20.000 or 50.000 (overcrowded). The distances and the number of plants depend on the broccoli variety, environmental conditions, and of course, the desired broccoli size that is always dictated by the market.
Broccoli Water Requirements and Irrigation Systems
Broccoli plants can not generally tolerate drought; the quality of the final product will be significantly decreased under water-stressed conditions. Thus, most professional producers irrigate their plants regularly even during winter. On the other hand, excess water may cause root rot, which leads to the entire plant collapse, and significant yield losses. Broccoli can collapse in 2-3 days under water-soaked conditions.
The most crucial periods when it comes to irrigation is first during the first stage until the seeds sprout and secondly during the flowery head formation. Most producers irrigate their plants, providing frequent amounts of water every other day. They provide small amounts of water during the first stages and increase them periodically, as the plant grows. During summer, irrigation sessions may have to be increased to one every day. Of course, water requirements can be different under different weather and soil conditions.
The most commonly used irrigation system in commercial broccoli farming is drip irrigation.
Broccoli Fertilization Requirements- How to grow healthy and thriving Broccoli
First of all, you have to take into consideration the soil condition of your field through semiannual or annual soil testing before applying any fertilization method. No two fields are the same. Nobody can advise you on fertilization methods, without taking into account your soil’s test data, tissue analysis, and crop history of your field. However, we will list the most common fertilization schemes used by a considerable number of farmers.
In most cases, Broccoli demands heavy fertilization in order to thrive and produce more than one head per plant. Thus, it is considered a hungry crop.
Many broccoli farmers apply a balanced fertilizer (N-P-K 20-20-20) at a total rate of 800kg per hectare throughout the growing period. They apply up to 400kg per hectare at transplanting or direct seeding, 200kg per hectare about 3-4 weeks later, and 200kg per hectare about 6 or 7 weeks after planting. We can add the granular fertilizers directly to the soil surface and irrigate. It is crucial that the granules don’t come in touch with the young plants, because there is a risk of burning them. Keep in mind that 1 hectare = 2,47 acres = 10.000 square meters.
However, most broccoli farmers choose the method of fertigation (injection of water-soluble fertilizers inside the drip irrigation system). In this case, they can apply different rates of fertilizers for each day.
However, these are just common patterns that should not be followed without doing your own research. Every field is different and has different needs. Checking the soil condition and pH is vital before applying any fertilization method. You can consult your local licensed agronomist.
Broccoli Weed Management
An important growing technique when growing Broccoli is weed management. Broccoli often suffers from weeds during the first stage of its development. Weeds compete with young plants in terms of space, access to sunlight, water, and nutrients. All broccoli growers must have a sound weed control strategy. The strategy may differ significantly between countries, law framework, means of production, the industry at which the product targets, etc. Manual weed control on a weekly basis is almost necessary in some cases (organic production). When the Broccoli has grown enough, weeds are not a major problem.
The majority of Broccolis are ready for harvesting 60-90 days after transplanting. However, harvest time depends on their variety mainly, as well as on the environmental conditions. We harvest broccoli by the time the heads have reached the suitable size of their variety. Heads should be compact and have a uniform coloring. We normally harvest the main, central head first. The side heads normally mature afterward. In order to promote the growth of a second head after the first has been harvested, we can continue our normal fertilization and irrigation scheme.
Harvest is done manually with scissors or knives during the evening. Otherwise, the sun may cause foliage wilting. Producers cut the heads free from leaves together with 10-15cm (0.4-0.6 inches) of the stem. Delayed harvest can significantly reduce quality, as there is a risk of heads to turn loose and yellow.
Right after harvesting, the broccoli heads are normally cooled immediately. This way, farmers and traders can ensure the quality of broccoli heads for a couple of days or weeks. The storage temperature can be approximately 0 °C ( 32℉) and the relative humidity levels close to 95%.
Broccoli Yield per Hectare
A good yield after years of experience would be 20 tons per hectare (1 hectare = 2,47 acres = 10.000 square meters). The weight of each plant depends on the variety and growing conditions. Broccoli farming, even though demanding, could offer significant profits. In recent years there is an increased demand for Broccoli in countries of Southern Europe and the Mediterranean. Over the past 25 years, there has been a 200% increase in US Broccoli production.
Broccoli Pests and Diseases
Most common broccoli problems
Pieris is a white caterpillar that attacks cruciferous plants. The larvae of the parasite feed on foliage, causing significant quality reduction and great yield losses. Once the cultivation has been attacked, management is more complicated. Since pests develop immunity against pesticides easily, the best method to control them is through biological management. Pheromone traps are a commonly used technique. They attract male insects preventing them from fertile females. Thus, traps somehow reduce their population.
Cabbage Root Fly
Delia radicum is one of the main broccoli pests. Newborn flies create tunnels on foliage to feed, causing the leaves to wilt and die. The pest attacks Broccoli late in spring or early summer. Once the crop has been attacked, management is more difficult. Since pests develop immunity against pesticides easily, the best method to control them is through biological management.
Downy mildew is a fungal disease caused by the pathogen Hyaloperonospora brassicae. The disease is favored by moist and warm conditions causing characteristic chlorotic spots on the upper foliage surface, combined with downy mold on the underside. The disease is dangerous as it leads to significant yield losses.
Disease control begins with proper precautionary measures. These include weed control and safe distances between plants, adequate drainage, and avoidance of foliar irrigation. The general condition of the plants (nutrients and water level, sun exposure) can also boost their immunity. Chemical treatment is used only if the problem is severe and always under supervision from a local licensed agronomist. It is also crucial to use proper sanitation, such as tools disinfection every time we touch the plants.
Powdery mildew is a disease caused by the fungus Erysiphe cruciferarum and could turn very serious, as it leads to yield losses. Symptoms include chlorotic spots. Under optimum temperature and moisture conditions, a powdery layer resembling flour develops on the upper side of the foliage. Management includes the same methods used for downy mildew control.
Alternaria is a serious disease favored by increased soil moisture conditions. The fungus Alternaria brassicae causes the disease. The pathogen infects all parts of the plant above the soil. Excess irrigation accelerates the disease cycle.