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Olericulture II is a unit that introduces undergraduate students taking BSc Horticulture to cool season crops and a few families of warm season crops, Herbs and Spices. It discusses ecology, factors affecting growth and development,crop management and cultural practices, pest and disease control, harvesting sorting, packaging and marketing.it includes the following families alliacea, asparagaceae, asteraceae, Brassicaceae, Chenopodiaceae, Fabaceae, Graminea and selected families of herbs and spices. Olericulture I is a pre-requisite for this unit

Icon objectives.jpg
  1. To introduce students to the main families of cool season vegetables, herbs and spices
  2. To discuss the physiology, production, harvesting and processing of main cool vegetable crops
  3. To expose the students to hands on experience on the growing, management and processing of the cool season vegetables
  4. To examine the students continuously on the concepts learnt

New Terminologies

cool season vegetables, vernalization, Allium cepa

About the course

The unit will take 14 teaching weeks and 2 weeks of examination. The course consists of 14 lectures with practicals. The minimum contact hours should be 45 and maximum contact hours 60 hours. The best way to take the course is to go chronologically chapter by chapter in sequence and during or after covering a family of vegetables practical exposure to the growing of the vegetable should be done. Alternatively, the student should raise the different categories of these vegetables one from each family planted at one week intervals as you progress with the theoretical materials. At the end of each chapter, self testing is recommended for before proceeding to the following chapter.



Methods used in the classification of vegetable crops include Botanical, Horticultural, classification based on the part of the plant consumed, classification based on growth period and seasonality, classification based on method of culture and classification based on temperature adaptation. Vegetables vary considerably in their temperature requirements and are usually divided into warm and cool season vegetable crops

Definition of Cool Season Vegetables

The cool season vegetable crops are those that originates from temperate regions and can withstand heavy and light freezing.

General Characteristics of Cool Season Vegetables

Cool season crops are normally biennials where they take two seasons to complete their life cycle. During the first season the vegetable undergoes vegetative growth and the after vernalization and overwintering, flowering is initiated and the flower stalk elongation occurs. Cool season vegetables can withstand winter and /or frost especially during their early development stages. They are normally planted in the spring or late summer and harvested in winter. They can be categorized as hardy or half hardy vegetable crops based mainly on the ability of the seed to germinate at low soil temperatures and of the young plants to withstand frosts but not necessarily true for full grown plants. Hardy vegetable crops include asparagus, broccoli, cabbage, leeks and rhubarb and half hardy include beet, carrot, cauliflower, celery, lettuce and parsnip. These vegetables need cold treatment to induce flowering a process called vernalization, these require 18-21oC for optimal growth. A classification on the basis of hardiness is valuable in determining when crops may be planted in a given region

Important Families

The important families of cool season vegetables include alliacea, asparagaceae, asteraceae, brassicacea and chenopodiaceae Alliaceae


Introduction The alliaceae family commonly known as the onion family was formerly calleed the amaryllidiaceae family. Most of the important vegetable in this family are in the genus allium and sometimes referred to as the alliums Characteristics The main characteristics include:

  1. characteristic onion smell and odour
  2. Biennials normally grown as biennials
  3. Bulbs are storage organs
  4. Leaves arise from underground stems with long sheathing bases
  5. There are about 300 widely scattered species in the genus allium

Important Vegetables

  1. Onion (Allium cepa)
  2. Garlic (Allium sativum)
  3. Leeks ( Allium porrum)
  4. Japanese bunching onion (Allium fistulosum)
  5. Rakkyo (Allium chinense)

Onion ()Allium cepa var cepa)

Classification, origin and History Onion belongs to the alliacea family. Onion has been used by man as far back as history records (3500BC). The cultivated species are probably native to the general area of S/E Asia. The ancient Egyptians thought highly of them and were used as offerings to their gods. Large quantities were eaten , used as medicine and mummification. The Romans gave the name ONION derived from the Latin word unionem or unio meaning single-referring to the single bulb. Botanical description A half hardy biennial fherb, normally grown for its bulb as an annual and only carried forward into a second year when seeds are required. Bulb is a truncate formed from thickened leaf bases (sheaths)outer layers are thin and fibrous. Leaves are alternately arranged on the stem and are produced from flattened conical basal stem, they are cylindrical and leaf blades are hollow. Flowers are greenish white. Seeds are smooth black, wrinkled when dry. Stem is a cone shaped structure from where leaves arise.

The structure of the onion is shown in diagram below

Environmental and Climatic response Cool season crop that will grow well over a wide range of temperatures but optimal temperatures range from 13 to 29oC.Onion plants perform well in terms of quantity and quality when temperatures are cool during the early stages and warm temperatures and end of the growth period. A dry atmosphere at harvest is desirable to obtain satisfactory curing of the bulbs. Onion requires high moisture during the vegetative growth, does well under irrigation. altitudes above 300m above sea level are recommended. Temperature and photoperiod affect flowering and bulbing. Bulbing is a process of swelling of leaf bases, cessation of leaf primordial initiation. Bulbing is mainly affected by daylength, the required daylengths depends on varieties/cultivars. Onion is a long day plant with respect to bulbing, premature bulbing can occur at longer daylengths. Tropical cultivars (9-12 hours), temperate cultivars 15-16 hours. Temperature is vital in flowering-vernalization-initiate and daylenths affects development of flower stalks. When selecting cultivars consider daylengths requirement. Onion can grow in practically all types of soil but prefer sandy loams, alluvial clay soils, friable, fertile, well supplied with humus and well drained. pH of 5.8-6. Cultivars Classification of cultivars is done according to the following criteria

  1. Daylength requirement
  2. Bulb color
  3. Maturity period

Cultivars grown in Kenya include

  1. Red bulbing varieties-red creole, bombay red, red Tropicana
  2. White bulbing varieties-white creole, Texaa Grano and Tropicana F1 Hybrid
  3. Yellow bulbing cultivars-Yellow BERMUDA-does not store well, has mild flavour ideal for salads
  4. Green bunching onion-non bulbing or spring onions


Onions and related Vegetables

Table1: Nutrient content of selected onion and related alliums, in 100g of raw edible part

Nutrient Onion bulb Onion leaf Garlic bulb Leeks Welsh onion
Water(g) 89.0 92.2 64.3 90.8 90.5
Energy(kcal) 36 23 98 22 34
Protein(g) 1.2 2.0 7.9 1.6 1.9
Fat(g) 0.2 0.5 0.6 0.5 0.4
Carbohydrate(g) 7.9 3.0 16.3 2.9 6.5
Fibre 1.5 1.5 4.1 2.8 not known
Ca(mg) 25 75 19 24 18
K(mg) 160 160 not known not known not known
P(mg) 30 29 170 44 49
Fe(mg) not known not known 1.9 1.1 1.2
Zn(mg) not known not known not known not known 0.52
Vitamin A(IU) not known not know Trace 1160 not known
Carotene (ug) 10 620 not known 735 not known
Ascorbic acid(mg) 5 26 17 17 27