eBusiness Weekly
Own Correspondent
General broccoli is a vegetable rich in vitamin C, protein, fibre and flavour. It is also known as a “Super Food”. Broccoli belongs to the “Brassica — Genus” fairly closely related to cabbage, brussels sprouts and cauliflower. Broccoli types are, large headed varieties, sprouting varieties and Romanesco varieties. Large headed are the standard type with heads weighing from 400 grammes up 850 grammes. Sprouting broccoli like purple sprouting and green sprouting broccoli produces numerous heads on long stalks and romanesco varieties produce elegantly swirled heads composed of symmetrically pointed spirals. These large plants need plenty of growing space.
In Zimbabwe the best growing climate for growing broccoli is during the cool weather conditions of winter. During the hot, wet conditions of summer the head sizes tend to be smaller. Consult a prime seed agronomist on which are the best varieties for winter and summer production. Tasty in each of its varieties, broccoli is easier to grow than its relatives cauliflower and brussel sprouts and can produce bountiful crops. Always in high demand on the dinner table.
Site selection
Broccoli grows very well in medium to medium heavy clay loam with good water holding capacity. It can be grown, however, in more sandier soils but will require more frequent irrigations and higher fertiliser rates. PH levels should be form 5,8–6,5 as broccoli likes to have an alkaline soil. Broccoli responds very well to compost and organic enriched soils. Levels round 25-35 tonnes of well-prepared compost or farm yard manure will benefit the crop and help reduce the levels of costly fertilisers. Make sure compost and manure are well broken down when put in the fields or root burn may occur. Chicken litter can also be used at 2-5 tonnes per hectare but must be well composted. If ploughing, plough to a depth of 30–35cm which will make sure the soil is prepared for good root development, but make sure any old plough pan is broken up. If ripping then discing is preferred, this is also a good way of preparing a tilth.
The soil should not be too cloddy, also not to fine. During winter months, plant if possible on north facing slopes to achieve better soil warmth. Spacing if planting on beds which are at 1,5m centre to centre the in row should be 30cm apart and two rows placed on the bed 50-60cm apart. This should give approximately 44 000 plants per hectare. Planting on the flat, rows can be 40cm apart and in row of 35cm apart. Higher plant populations give smaller heads so populations should be governed by market requirements.
Fertiliser application
Broccoli can be susceptible to hollow stem problems caused by a boron deficiency. If there is a boron deficiency in the soil apply solubor as a foliar spray every two weeks at a rate of 10grammes /1 litre water. A balanced basal type fertiliser of either “A” “B” or “C” should be applied before planting. A vicon spreader can be used to broadcast the fertiliser on the flat or a ridger type applicator to apply the fertiliser if the crop is to be grown on beds.
Cupping with fertiliser cups by hand into the pre-marked planting holes can also be done but the fertiliser must be well mixed in the hole with the soil to prevent root burn.
On soil analysis results the rates of fertiliser can be adjusted to the rate to be applied and if compost or manure have been applied the rate can also be reduced.
Fertiliser rates of 500kg-750kg per hectare can be applied. Broccoli requires around 400kg per hectare of AN split into three applications from three weeks up to six weeks after transplanting.
If the crop is being planted on sandier soils and also during the rainy season extra top dressings might be required after heavy leaching rains. Plantings going into mid-winter should be top dressed with calcium nitrate, instead of AN as it works quicker in cool soils.
Seedlings planting is the most practical method. Use a recognised nursery like Prime Plants Nursery where strong and healthy seedlings are produced. By transplanting good seedlings this gives a base for a more uniform crop helping with reduced costs at harvest time.
Order around 10 percent more seedlings for your selected plant population from the nursery to ensure best seedling selection when transplanting. When using seedlings, at transplanting make sure that good plug to soil contact is made so the root system can leave the plug and quickly enter into the soil enriched with either fertiliser or compost.
Planting
Plant the seedlings as soon as possible after collecting them from the nursery to avoid the tiny hair roots from drying out. Plant the plugs/seedlings into pre irrigated soils in which the field has been brought up to field capacity.
After transplanting a light settling in irrigation is required to remove tiny air pockets between the plug and the soil. Varieties selection of a variety depends if it is to be marketed as fresh or frozen.
Broccoli is usually a cool weather crop but can be grown year round with correct variety selection, this is where your prime seed agronomist can advise. Broccoli is quite frost tolerant. There are two types, heading and sprouting. Sometimes selected varieties might produce side shoots once the main head has been harvested. Variety selection will also have maturity dates varying from 60-75 days.
Harvesting
Time of harvest is primarily determined by the tightness of the florets and not by the size of the head. The head should be firm and compact, not opening and loose. If leafy points have come through the head before harvest, it shows harvesting is late, or the plant has been under stress. This is more common in hot summer weather conditions when head size is generally smaller than in winter production.
When harvesting cut the central stalk at a 45 degree angle, 13-20cm below the head. This will keep water from pooling inside the cut stem and causing rot. Broccoli has a poor shelf life at ambient temperatures so the harvested heads will require cold storage or if being delivered to the market fresh, in the shortest possible time.
Brown or purple beads is a physiological problem that is more prevalent under hot humid conditions.
Irrigation
Regular water applications during the dry winter months is essential. Overhead irrigation or centre pivot irrigation is the most common followed by flood and more recently drip irrigation which is becoming more affordable.
Broccoli irrigations must be spot on or “Hollow stem” will occur due to fluctuations of water levels in the soil. Approximately 600mm-750mm of irrigation should be allowed for to produce a quality broccoli crop.
Therefore planning water usage from dams, rivers and boreholes can be worked out to match hectares to be planted. As the plant increases in size and leaf area, and the head starts to form, the amount of water required also increases. Irrigation should be planned on a weekly basis and the soil depletion area checked regularly to plan for the next irrigation cycle. A quick test is to take a fist full of soil in your hand, squeeze it to form a ball then tap the “ball” with your finger. If it collapses it is becoming dry and irrigation should be applied immediately. Preferably it should not have gone as far as this stage. The use of an evaporation pan should help with scheduling.
