Introduction
- A vegetable is any crop that is grown and eaten fresh.
- Vegetables are important both for nutritional and commercial reasons.
- They are categorized based on the part used as food, such as leaves, stems, roots, fruits, flowers, pods, and bulbs.
Vegetables are grouped into the following categories:
- Leaf vegetables, for example, kales and cabbages.
- Root vegetables, for example, carrots, beets, radishes, and turnips.
- Fruit vegetables, for example, French beans and okra.
- Stem vegetables, for example, asparagus, leeks, and spring onions.
- Bulb vegetables, for example, bulbed onions and garlic.
Tomatoes (Lycopersicon esculentum)
- Tomatoes are fruit vegetables widely grown in Kenya.
- The ripe fruit may be eaten raw, cooked, or processed to make tomato sauces, juices, and pastes.
Ecological Requirements
- Altitude: 0-2100m above sea level.
- Rainfall: 750-1300mm per annum.
- Soils: deep, fertile, and well drained.
Varieties
- Fresh market varieties:
- Money maker,
- Marglobe, Hundred fold,
- Beef eater,
- Hot set,
- Super marmande,
- Ponderosa.
- Processing varieties:
- Kenya beauty,
- San-marzano,
- Roma,
- Heinz 1350,
- Primabel,
- Rutgers hybrid,
- Cal-J.
Nursery Practices
- Choose a site which has not been grown with Solanaceae crops in the last three years.
- Nursery beds are raised about 15cm above the ground level.
- Make drills 20cm apart and 1cm deep, then cover the seeds.
- Provide shade or mulch material.
- Water twice a day.
- Apply phosphatic fertilizers during planting.
Seedbed Preparation
- The land should be dug deeply to control weeds.
Transplanting
- Seedlings are ready for transplanting when they are 10-15cm high after about one month.
- Holes are made at a spacing of 60cm x 90cm.
- Apply 20gm of DSP in the planting hole.
- Transplant with a ball of soil around the roots.
- Apply mulch around each seedling.
- Transplanting is normally done in the evening or on a cloudy day.
Field Maintenance
- Early control of weeds is necessary.
- Top dressing is done after the crop establishes.
- Pruning and staking are done to train the plants to grow vertically.
Pest Controls
- American Bollworm
- Nature of damage: boring holes on the fruits.
- Control: spraying insecticides.
- Tobacco White Fly
- Nature of damage: suck plant sap from the underside of the leaf, hence may transmit viral diseases.
- Control: destroy infected plants and spray insecticides.
Disease Control
- Late Blight
- Cause: fungus.
- Symptoms: dry patches on the leaves and fruits.
- Control: use of fungicides, crop rotation, and destruction of affected materials.
- Blossom-end Rot
Caused by:
- Too much nitrogen in early stages.
- Irregular or infrequent watering.
- Calcium deficiency.
- Control: apply calcium ammonium nitrate and correct the above problems.
Harvesting
- For canning, fruits should be fully ripe.
- For fresh market, fruits should be partially ripe and packed in crates to avoid damage.
- The fruits should be graded according to size, colour, ripeness, and freedom from blemishes.
Cabbage
- Cabbage is a leaf vegetable related to other brassica crops such as kales, cauliflower, Chinese cabbage, and Brussels sprouts.
- Cabbage leaves may be eaten raw in salads, steamed, boiled, or cooked in a variety of ways.
- The leaves can also be fed to livestock.
Ecological Requirements
- Altitude:
- Those with small heads: 900-1500m above sea level.
- Those with large heads: 1800-2700m above sea level.
- Temperature: require cool conditions.
- Rainfall:
- 750-2000mm per annum, well distributed throughout the growing period.
- Soils:
- Deep, fertile, and well drained.
Varieties
- Early maturing:
- Brunswick,
- Sugar loaf,
- Early jersey,
- Copenhagen market,
- Chinese cabbage,
- Celery cabbage,
- Cafe splits kool,
- Gloria, Mukuki,
- Golden acre.
- Late maturing:
- Drumhead,
- Savoy,
- Perfection,
- Winningstadt.
Nursery Practices
- The beds should be raised, 1 m wide and any convenient length (usually 2-3m).
- Make drills 15-20cm apart.
- Sow seeds by drilling and cover to a depth of 1 cm.
- Provide shade or mulch material.
- Apply phosphatic fertilizers and mix thoroughly with soil during planting.
- Water twice a day.
Seedbed Preparation
- Cultivation should be done during the dry season so that all the weeds are killed.
- Dig holes at the spacing of 60cm x 60cm.
- Incorporate farmyard manure in the soil.
Transplanting
- Water the seedlings before uprooting.
- Seedlings are ready for transplanting after one month, when they are 10-15cm in height.
- Select healthy and vigorous seedlings.
- Transplant the seedlings with balls of soil to prevent root damage.
- Plant to the same depth as they were in the nursery.
Field Maintenance
- Apply fertilizers during planting and top dress later.
- Control weeds to reduce competition.
Pest Control
- Diamond Black Moth
- Damage: Eats the underside of the leaf making windows or holes in the leaf.
- Control: Spray recommended insecticides.
- Cutworms
- Damage: Attacks the stem at the ground level causing the plant to fall.
- Control: Spray recommended insecticides.
Disease Control
- Black Rot
- Cause: Bacteria.
- Symptoms: Leaves turn yellow and rotting of the stem giving an offensive odour.
- Control: Closed season, crop rotation, use certified seeds, and spray appropriate chemicals.
- Black Leg
- Cause: Fungus.
- Symptoms: Brown to black spots on seedlings and dark canker on the stem.
- Control: Crop rotation, destroy infected materials.
Harvesting
- Cabbages are ready for harvesting 3-4 months after transplanting.
- The heads are cut when they are solid and compact.
- Harvested cabbages are sold immediately.
Carrots (Daucus carota)
- Carrots are root vegetables grown in the cool areas of Kenya.
- They are commonly eaten raw in salads but can also be cooked.
Ecological Requirements
- Altitude: 0-2,900m above sea level.
- Rainfall: 750 – 1,000mm, well distributed throughout the growing period.
- Soils: Requires deep, fine tilth, well drained soils that are free from obstacles to allow for root expansion.
- Temperatures: Requires cool to warm temperatures; very high temperatures result in pale and short roots.
Varieties
- Fresh market varieties, for example, Chantenay and Nantes.
- Canning varieties, for example, Nantes.
- Fodder varieties, for example, Oxhast.
Land Preparation
- The field should be well dug to a depth of about 20cm.
- The soil clods should be broken to give a fine tilth before planting.
- Manure should not be applied as it induces forking which reduces the crop quality.
Planting
- Carrots are planted directly into the main seedbed.
- Seeds are drilled into rows made 20-30cm apart.
- The seeds are then covered lightly and the soil pressed down.
- 90kg/ha of DSP should be applied at planting time in the drills.
- It should be mixed well with the soil before placing the seeds.
Field Practice
- Thinning – done 2 weeks after germination to allow proper spacing.
- Weed control – the field should be kept weed free to reduce competition.
- Earthing up – done while weeding to encourage root expansion.
- Topdressing: after weeding, 60kg of nitrogen per hectare should be applied as top dress.
- Irrigation – carried out when rainfall is insufficient.
Pest Control
- Carrots have few field pests except green aphids.
- These can be controlled by using appropriate pesticides.
Disease Control
- Occasionally attacked by mildews, especially in wet and humid environments.
- Thinning can be done to reduce humid conditions and prevent disease spread.
Harvesting and Marketing
- Carrots are ready for harvesting 3-5 months after planting, depending on the variety.
- They are lifted from the soil and sold fresh or canned.
Onions (Allium cepa)
- Onions are bulb vegetables grown in the warm areas of Kenya.
- They are used as a vegetable in salads and for flavouring foods, soups, and stews.
Ecological Requirements
- Altitude: 0-2,100m above sea level.
- Rainfall: 1,000mm of rain per year; irrigation is necessary in dry areas.
- Soils: Requires well drained fertile soils.
- pH: 6.0 – 7.0.
- Temperatures: Onions are warm climate crops, though some varieties prefer cool conditions.
- They require a fairly long dry period for ripening.
Varieties
- Red creole,
- Tropicana hybrid,
- White creole.
Land Preparation
- The land should be well prepared leaving a fine tilth.
- Farmyard manure at 40 – 50 tonnes per hectare should be applied and mixed well with the soil.
Planting
- Direct: Seeds are drilled in rows 30cm apart and 8cm within the rows. 20kg/ha of DSP fertilizer is used.
- Indirect: Seeds are established in nurseries before transplanting them in rows 30cm apart and 8cm within the rows.
- Shallow planting is recommended for bulb expansion.
Field Management Practices
Thinning
- Carried out only in directly planted crops to achieve spacing of 8cm between two plants within the row.
- The thinned plants, referred to as spring onions, are used as vegetables in salads.
Topdressing
- Calcium ammonium nitrate at the rate of 250kg per hectare is recommended for topdressing onions.
- This is done 3 months after planting.
Pest Control
Onion Thrips:
- These cause silvering and withering of leaves from the tips downwards.
- They are controlled by spraying with appropriate insecticides such as Diazinon or Fenthion.
Disease Control
Purple Blotch and Downey Mildew
- Purple blotch: characterized by oval greyish lesions with purple centres on leaves, causing leaf curling and die back.
- Downey mildew: characterized by brown spores covering the leaves leading to death of the whole plant.
- Both diseases are effectively controlled by crop rotation and application of appropriate fungicides.
Harvesting and Marketing
- Onions are ready for harvesting 5 months after planting.
- When leaves start drying, the tops are broken or bent at the neck to hasten withering of the stems.
- The bulbs are then dug out and left to dry in a shade for a few days.
- Onions are graded according to size and marketed in nets of about 14-16kgs.
