Agroforestree Database

Local names:
 Arabic (al-kharoubah,kharrub), Catalan (garrover,garrofer), English (St. John’s bread,locust bean,carob tree,carob bean), French (caroubier), German (karubenßaum,johannisbrotßaum), Greek (charaoupi), Hindi (kharnub), Italian (carrubo), Malay (gelenggang)

Ceratonia siliqua is an evergreen shrub or tree up to 10 m high, crown broad semi-spherical, thick trunk, brown rough bark and sturdy branches.

Leaves 10-20 cm long, alternate, pinnate, with or without a terminal leaflet. Leaflets 3-7 cm long, ovate to elliptic, 4-10 normally opposite pairs, coriaceous, dark green and shiny above, pale green beneath finely veined with margins slightly ondulate, tiny stipules. 

Flowers green-tinted red, small, numerous, 6-12 mm long, spirally arranged along the inflorescence axis in catkin-like racemes borne on spurs from old wood and even on the trunk (cauliflory). Pentamerous symmetry with calyx but not corolla placed on a short pedicel. Calyx disc-shaped, reddish-green, bears nectaries. Females consist of a pistil (6-8.5 mm) on a disk and rudimentary stamens, 5 hairy sepals. Males consist of a nectarial disk, 5 stamens with delicate filaments hairy sepals. In the centre of the disk there is a rudimentary pistil. Hermaphrodite flowers a combination; containing a pistil and a complement of 5 stamens.

The fruit indehiscent pod, elongated, compressed, straight or curved, thickened at the sutures, 10-30 x 1.5-3.5 cm, about 1 cm thick with blunt or subacute apex. Pods brown, wrinkled surface, leathery when ripe. Seeds occur in the pod transversally, separated by mesocarp; very hard, numerous, compressed ovate-oblong, 8-10 x 7-8 mm, 3-5 mm thick; testa is hard, smooth, glossy brown, hilium minute. 

The scientific name of the carob tree derives from the Greek ‘keras’, horn, and Latin ‘siliqua’, alluding to the hardness and shape of the pod. The common name originates from the Hebrew-'kharuv’, from which other vernacular names are derived.

Ecology

A long-lived evergreen and thermophilic tree thriving in habitats with mild Mediterranean climates. It grows well in warm temperate and subtropical areas, tolerates hot and humid coastal areas. It is a xerophytic species, well adapted to the ecological conditions of the Mediterranean region. C. siliqua, together with Olea europea var. sylvestris, forms one of the most characteristic associations of the lowest Mediterranean vegetation zone and is thus considered a climax community (Olea-Ceratonion). Areas suitable for C. siliqua should have a subtropical Mediterranean climate with cool, not cold, winters, mild to warm springs, and warm to hot, dry summers.

Cannot withstand waterlogging although the root system is usually deep. The tree’s extensive root system penetrates the soil deeply; roots develop under stressful conditions to explore deeper layers where water may be available; it can thus survive long periods of drought. In addition the leaves can maintain turgor under situations of drought, using different strategies according to the season. 

Sensitivity to frost is a serious problem in this crop. The extent of frost damage depends on the temperature within the orchard and the physiological state of the trees.  Noted for its drought resistance, the plant is especially useful where irrigation is impractical or rainfall unreliable. However, unless irrigated, the fruits are dry and shrivelled, having little commercial value, and the yields are very low. Although drought-resistant, C. siliqua trees do not bear commercial crops unless they receive at least 500-550 mm/year, but 350 mm of annual rainfall is considered enough for fruit set.

Native range
Cyprus, Egypt, Israel, Jordan, Lebanon, Libyan Arab Jamahiriya, Saudi Arabia, Syrian Arab Republic, Tunisia, Turkey

Tree management

Seedling rootstocks, before or after budding, are usually planted from pots directly into the orchard. Trees with well-developed roots should be used for transplanting, and proper care during and after planting is essential.

For dryland orchards on poor soils on the Mediterranean coast, tree densities between 100 and 175 trees/ha are recommended, that is, spacing from 9 x 9 m to 7 x 8 m. When C. siliqua is to be planted in fertile soils, high-density planting and tree thinning later may be considered. Little pruning is necessary due to the tree’s specific growth and fruiting habits.

If male and hermaphroditic trees are planted as pollinators they must be interspersed around and within the orchard in a regular pattern. It is important to use different types of male or hermaphroditic pollinators to overlap with female cultivar bloom, as main cultivars often display a long blooming season of 3-4 months. Since male trees have a shorter flowering period than hermaphrodites, the latter usually show better overlapping.

Orthodox seed storage behaviour; viability can be maintained for 5 years in air-dry storage at 5 deg. C without loss in viability. Although carob seeds have remained viable for as long as 5 years stored at low temperatures in sealed containers, it is advisable to use seeds from the current season. Seeds are presumably viable after passing through an animal’s digestive tract. There are about 500 seeds/kg.

A long-lived evergreen and thermophilic tree thriving in habitats with mild Mediterranean climates. It grows well in warm temperate and subtropical areas, tolerates hot and humid coastal areas. It is a xerophytic species, well adapted to the ecological conditions of the Mediterranean region. C. siliqua, together with Olea europea var. sylvestris, forms one of the most characteristic associations of the lowest Mediterranean vegetation zone and is thus considered a climax community (Olea-Ceratonion). Areas suitable for C. siliqua should have a subtropical Mediterranean climate with cool, not cold, winters, mild to warm springs, and warm to hot, dry summers.

Cannot withstand waterlogging although the root system is usually deep. The tree’s extensive root system penetrates the soil deeply; roots develop under stressful conditions to explore deeper layers where water may be available; it can thus survive long periods of drought. In addition the leaves can maintain turgor under situations of drought, using different strategies according to the season. 

Sensitivity to frost is a serious problem in this crop. The extent of frost damage depends on the temperature within the orchard and the physiological state of the trees.  Noted for its drought resistance, the plant is especially useful where irrigation is impractical or rainfall unreliable. However, unless irrigated, the fruits are dry and shrivelled, having little commercial value, and the yields are very low. Although drought-resistant, C. siliqua trees do not bear commercial crops unless they receive at least 500-550 mm/year, but 350 mm of annual rainfall is considered enough for fruit set.

Carob seed germinates easily, but the hard coat requires treatment with tap water, boiling water, sulphuric acid (H2SO4), or gibberellic acid (GA3). Optimum temperature for germination is 25 deg. C. Different potting mixtures can be used, usually containing soil, humus, perlite and peat moss, and usually amended with sand to improve drainage and structure.

C. siliqua is difficult to root; its potential for developing adventitious roots is low, but rooting has been obtained on subterminal hardwood cuttings (2 or 3 years old). Rootstocks must produce a well-developed rooting system. Seedling stocks are budded 1 year after germination, in the nursery, or 2 years from germination, after planting in the orchard.

Since it requires little if any cultivation, tolerates poor soils and is long lived, C. siliqua is often recommended for reforestation of degraded coastal zones threatened by soil erosion and desertification.

  Carob pulp is high in total sugar content (48-56%). In addition, it contains about 18% cellulose and hemicellulose. Mineral composition consists of potassium, calcium, magnesium, sodium, iron, copper, iron, manganese and zinc. In some countries, Egypt for example, carob syrup is a popular drink, obtained from carob kibbles with water. Unicellular organisms convert carob pulp into a high-protein feed; sugar solutions extracted from carob pods are an excellent substrate for culturing fungi such as Aspergillus niger and Fusarium monoliforme, and the dried mycelium is a palatable and nutritious feed, containing up to 38% crude protein by weight. The carob product most widely used, especially in the food industry, is carob bean gum (CBG), or locust bean gum (LBG). This gum comes from the seed endosperm and chemically is a polysaccharide, a galactomnnan. 100 kg of seeds yield 20 kg on average of pure dry gum.  The mucilaginous gum, known as ‘tragasol’, is used in a wide range of commercial products as a thickener, stabilizer, binder and gelling or dispersal agent. The food industry uses CBG for the production of a large number of different commodities: ice cream, soups, sauces, cheese, fruit pies, canned meats, confectionery, bakery products and pet foods. Technical applications of CBG include cosmetics, pharmaceuticals, film emulsions, paints, polishes, ceramics and adhesives.  Pulp extracted and purified produces sugar and molasses. Powdered pulp is used as a food ingredient and cacao substitute and for preparing dietary products. Carob powder consists of 46% sugar, 7% protein and small amounts of numerous minerals and vitamins and is thus quite nutritious. Carob ‘cocoa’ has an advantage over chocolate in that it has fewer calories and neither caffeine nor theobromine. Ground seed embryo and endosperm can be used for human consumption; the latter, containing CBG and E-410, is a food additive and a dietary fibre.

Fodder: C. siliqua pods provide fodder for ruminants and non-ruminants. Endosperm and embryo of the seed can be ground and used for pet food. The fodder is now being used in zero-grazing in Mediterranean countries.

The wood produces a slow-burning charcoal and can also be used for firewood.

Timber: C. siliqua timber is hard and close-grained and has been used to make utensils.

Shade or shelter:  Widely planted as a shade tree, also recommended as a windbreak around orchards.

Tannin or dyestuff:  Ripe carob pods contain large amounts of condensed tannins (16-20% of dry weight). 

Medicine:  Tannins extracted from the pulp act as an anti-diarrhoetic. Ground pulp and seed endosperm are used in the preparation of pharmaceutical products. 

Gum or resin:  Currently, the main use of the seed is gum extraction. 

Ornamental:  A popular ornamental in California, Australia and elsewhere; male trees are preferred as they do not provide litter from pod fall. However, the value of C. siliqua as a drought-tolerant, air-pollution tolerant, low maintenance tree for street landscape planting could be limited by its large size when mature and its strong, invasive roots.

Intercropping:  Frequently planted with species such as olive, grapevines or almond. Young C. siliqua orchards are intercropped with early-bearing species such as peach, almond or even vegetables; an annual perennial crop between the rows may give early returns to the investment. 

Alcohol:  A high sugar content and its relatively low cost have made carob pulp among the earliest horticultural crops used for the production of industrial alcohol by fermentation in several Mediterranean countries.

Pollution control:  Could help buffer noise from factories, roads and railways because of its dense foliage.