Broccoli, a little grown crop with huge rewards

Broccoli is a floral vegetable, which belongs to the brassica family that include vegetables such as cabbage, cauliflower, Brussel sprouts, collard greens and Chinese cabbage.

Their only difference with cabbages is that while the latter forms a head, broccoli forms green curds. The edible part is the green flower buds and stems.

Brocolli is mainly grown under irrigation and rain-fed conditions. Its production is increasing due to its medicinal properties.

There is also a growing demand in hotels and supermarkets as well as for export.

The major limitation in the production of this crop is low domestic demand as most of the consumers don’t know how to prepare it. Main producing regions are Kiambu, Nairobi, Laikipia, Murang’a, Makueni and parts of Rift valley.

Ecological requirements

Moderately uniform cool temperatures are best for growth and quality of broccoli. Too much heat can prevent curd formation. Exposure to cool temperatures of less than 100C after planting results to bolting (premature formation of flowers) and this leads to formation of small heads called ‘buttons’.

The optimum temperature range for curd formation is 13.9-200C. Above 200C, quality is reduced. Above 250C, curds may not form at all.

As temperatures near freezing, injury occurs and there is no curd development. High temperature during curd development may result in loss of compactness and development of ricey curds.

Suitable soils are those that are well-drained, friable and with high water-holding capacity. The best soil pH is 5.5–6.5.

The crop requires constant water supply for good growth and yields. Therefore, where rainfall is inadequate, irrigation water should be available.

Broccoli has a relatively high requirement for Molybdenum (a mineral element).

Molybdenum deficiency occurs in acidic soils with pH less than 5.5. Molybdenum deficiencies can be corrected by liming foliar fertiliser applications or seed treatment.

Planting
Broccoli can be directly seeded or first planted in a nursery bed. Transplanting is done after four to six weeks or when 8-10cm high or when the seedlings have three to four fully developed leaves.

The spacing in the field, whether direct seeded or transplanted is 45-90cm between rows and 30-60cm within rows.

Fertiliser application

Broccoli is a heavy feeder of nitrogen and potassium. Organic matter, phosphorous and potassium fertilisers should be applied before transplanting.

Top-dressing using nitrogenous fertilisers is done four weeks after transplanting and three weeks, thereafter. Rates are 5-10g/plant (185-370 kg/ha) of CAN and 200 kg/ha DSP.

Irrigation

Broccoli has a shallow root system and, therefore, when the plants are growing, they will require constant availability of moisture.

Adequate moisture promotes production of large heads. Lack of adequate moisture may lead to tough, fibrous stalks and tip-burn of the plant.

Weed control

Broccoli is shallow rooted and care should be taken not to damage roots in the field as this would encourage entry of fungi and bacteria.

Clean weed control should be practised to avoid competition for water and nutrients.

Mulching may also be carried out for weed control and moisture conservation.

Pests

Aphids: They suck sap, causing curling of leaves and transits viruses.

Control: Systemic insecticides; biological – use of lady bird and beetle and cultural by intercropping and mulching using coloured mulch can be used.

Diamond back moth: The caterpillar causes damage to broccoli. It is the worst pest to brassicas worldwide. It feeds on leaf lamina from the underside causing windowing effect.

Control: Use of chemicals; biological control – Bacillus thuringiensis and cultural, which is intercropping with strong smelling crops like garlic, parsley

Cut worm: Larvae feed on stem base cutting it off. It is more serious at transplanting.

Control: Chemical dusting around stem bases of transplants, using chemical baits (sugar in water and poison) and cultural, unearth larvae and kill them.

Diseases
Black Rot: Caused by Xanthomonas campestris pv campestris. Characterised by yellow angular spots that progress inward from the leaf margin. Leaf veins become dark brown to black and heads may be deformed.

Control: Crop rotation with crops that are not related to broccoli. Use of clean seeds for planting, use of clean transplants, use of resistant varieties and practising good sanitation.

Alternaria leaf spot: Caused by Alternaria brassicae. Symptoms include yellow, concentric spots on foliage. Infected broccoli seedlings may be stunted or killed.

Control:Use of crop rotation and clean seeds.

Downy Mildew: Caused by Peronospora parasitica. The symptoms are yellow spots on the upper surface with bluish white fungal growth on the lower surface of leaves.

Control: Crop rotation, practising good sanitation, and weed management.

Damping off: Caused by Rhizoctonia solani or Phytium spp. It’s a fungal disease and is more problematic at the nursery stage. It causes a dark brown or black rot at stem base of seedlings resulting into death.

It is common in overcrowded and or over-watered nurseries.

Control: Use of fungicides, avoid overcrowding and over watering of seedlings

Harvesting

Broccoli takes 45 to 60 days after transplanting before harvesting can begin. The marketable part of broccoli is the upper stalk and clusters of unopened flower buds.

The central heads are ready to use when buds are well-formed and before they begin to show any yellow colour. Side shoots form after the central heads are cut; these can continue to be harvested for some time.

Broccoli is harvested while the inflorescence is still immature and compact before the individual flower heads open. Over mature heads develop tough, woody fibres in the stems, making the product unmarketable.

***
Ms Mutua works in Department of Crops, Horticulture and Soils, Egerton University.

BENEFITS OF BROCCOLI

• Good source of dietary fibre, which facilitates good digestion.
• Maintains a healthy heart by reducing cholesterol.
• Keeps the skin young and glowing.
• Contains anti-cancer substances.
• It is a natural antibiotic.
• Rich in anti-oxidants.
• Rich in calcium, potassium, Vitamin C and protein.
• Has anti-viral properties.
• Protects eyes.
• Cleanses the intestines.
• Good for bone health as it contains calcium and potassium.
• Reduces blood sugar as it contains soluble fibre.