Pomegranate
(Punica granatum)
Cultivation and Farming
Soils and Climate
Soil - Pomegranates are fairly drought tolerant and can be grown on either calcareous or acid soils. Climate - Grow best in dry climates with mild winters. Chilling requirement - Unclear; can be grown in tropical climates without chilling. Cold hardiness - Wood tolerates temperatures down to -11°C.
The pomegranate thrives on calcareous, alkaline soil and on deep, acidic loam and a wide range of soils in between these extremes
Propagation
Pomegranate seeds germinate readily even when merely thrown onto the surface of loose soil and the seedlings spring up with vigor. However, to avoid seedling variation, selected cultivars are usually reproduced by means of hardwood cuttings 25-50 cm long. Treatment. indole-butyric acid and planting at a moisture level of 15.95% greatly enhances root development and survival. The cuttings are set in beds with 1 or 2 buds above the soil for 1 year, and then transplanted to the field. Grafting has never been successful but branches may be air-layered and suckers from a parent plant can be taken up and transplanted.Pollination
The pomegranate is both self-pollinated and cross-pollinated by insects. There is very little wind dispersal of pollen. Self-pollination of bagged flowers has resulted in 45% fruit set. Cross-pollination has increased yield to 68%. In hermaphrodite flowers, 6 to 20% of the pollen may be infertile; in male, 14 to 28%. The size and fertility of the pollen vary with the cultivar and season
Cultivar
Types with relatively soft seeds are often classed as "seedless". Among the best are 'Bedana' and 'Kandhari'. 'Bedana' is medium to large, with brownish or whitish rind, pulp pinkish-white, sweet, seeds soft. 'Kandhari' is large, deep-red, with deep-pink or blood-red, subacid pulp and hard seeds. Others include:
'Alandi'('Vadki')–medium-sized, with fleshy red or pink, subacid pulp, very hard seeds.
'Dholka'–large, yellow-red, with patches of dark-pink and purple at base, or all-over greenish-white; thick rind, fleshy, purplish-white or white, sweet, pulp; hard seeds. The plant is evergreen, non-suckering, desirable for commercial purposes
'Kabul'–large, with dark-red and pale-yellow rind; fleshy, dark-red, sweet, slightly bitter pulp.
'Muscat Red'–small to medium, with thin or fairly thick rind, fleshy, juicy, medium-sweet pulp, soft or medium-hard seeds. The plant is a moderately prolific bearer.
'Paper Shell'–round, medium to large, pale-yellow blushed with pink; with very thin rind, fleshy, reddish or pink, sweet, very juicy pulp and soft seeds. Bears heavily.
'Poona'–large, with dark-red, gray or grayish-green rind, sometimes spotted, and orange-red or pink-and-red pulp.
'Spanish Ruby'–round, small to medium or large; bright-red, with thin rind, fleshy, rose-colored, sweet, aromatic pulp, and small to medium, fairly soft seeds. Considered medium in quality.
'Vellodu'–medium to large, with medium-thick rind, fleshy, juicy pulp and medium-hard seeds.
'Muscat White'–large, creamy-white tinged with pink; thin rind; fleshy, cream-colored, sweet pulp; seeds medium-hard. Bears well. Desirable for commercial planting in South Africa
Culture
Rooted cuttings or seedlings are set out in pre-fertilized pits (60 cm) deep and wide and are spaced 3.5-5.5 m apart, depending on the fertility of the soil. Initially, the plants are cut back to 60-75 cm in height and after they branch out the lower branches are pruned to provide a clear main stem. Inasmuch as fruits are borne only at the tips of new growth, it is recommended that, for the first 3 years, the branches be judiciously shortened annually to encourage the maximum number of new shoots on all sides, prevent straggly development, and achieve a strong, well-framed plant. After the 3rd year, only suckers and dead branches are removed. For good fruit production, the plant must be irrigated.
Pests and Diseases
Pomegranate butterfly, Virachola isocrates, lays eggs on flower-buds and the calyx of developing fruits; in a few days the caterpillars enter the fruit by way of the calyx. These fruit borers may cause loss of an entire crop unless the flowers are sprayed 2 times 30 days apart. A stem borer sometimes makes holes right through the branches. Twig dieback may be caused by either Pleuroplaconema or Ceuthospora Phyllosticta. Discoloration of fruits and seeds results from infestation by Aspergillus castaneus. The fruits may be sometimes disfigured by Sphaceloma punicae. Dry rot from Phomopsis sp. or Zythia versoniana may destroy as much as 80% of the crop unless these organisms are controlled by appropriate spraying measures. Excessive rain during the ripening season may induce soft rot.
Minor problems are leaf and fruit spot caused by Cercospora, Gloeosporium and Pestalotia sp.; also foliar damage by whitefly, thrips, mealybugs and scale insects; and defoliation by Euproctis spp. and Archyophora dentula. Termites may infest the trunk.
Training Young Trees
Trees may be trained to a bush, single- or multiple-trunked tree. The bush form is satisfactory for backyards or hedgerows, but is undesirable for good commercial production.
Trees form the nursery are planted bare root in winter or early spring. The natural growth habit of the pomegranate is to produce many suckers from the base of the tree. If a single truck tree is desired, only one vigorous sucker or the trunk of the original nursery tree should be selected and branches grown from it. Basal suckers should be removed periodically to promote growth form the main trunk of the newly planted tree. If the orchard trees are to be developed into a multiple-trunk system, five or six vigorous suckers should be selected around the base of the young tree and allowed to grow.
Selection of the five or six suckers to be developed into permanent trunks may take two or three or more years until good trunks are correctly positioned to form a sturdy and symmetrical tree. All other suckers should be removed in summer and during dormant pruning.
Many growers prefer the multi-trunk system. In case of frost injury, usually only one or two trunks are injured, leaving the others to continue bearing. New trunks can be trained from suckers and full production restored to the tree in 2 or 3 years. Single-trunked trees may be completely killed except for suckers coming form the ground. Trees trained to a multiple truck require less frequent care in pruning during the first few years and come into bearing sooner than trees having only one truck.
Some pruning and tying with ropes for support may be needed for the first 3 or 4 years or until trunks are large and rigid enough to support the developing top.
Pruning
Pomegranate trees require a small amount of pruning each winter to maintain shape and good bearing surface. Even mature trees grow vigorously, sending up a large number of shoots and basal suckers that require removal each year.
The short spurs on 2- or 3-year-old wood growing mostly on the outer edge of the tree produce flowers. These spurs develop on slow growing, mature wood that bears fruit for several years, but as the tree increases in size the wood loses its fruiting habit. Light, annual pruning encourages growth of new fruit spurs and heavy pruning reduces yields. Care should therefore be taken to leave adequate fruit-bearing wood on the tree, while removing crossing over or interfering branches. In addition, some thinning out of crowded bearing areas helps produce larger fruit having fewer wind scars.
Should below-freezing temperatures occur in early winter before trees are fully dormant, or in early spring when trees are beginning to leaf out, severe damage can be done to tree trunks. Occasionally, entire trunks are girdled and killed by frost. Remove weak or dead limbs during the next growing season, and permit a vigorous sucker to develop from ground level to replace it.
Fertilization
Mature pomegranate trees require from 1-2kg of actual nitrogen per tree per year. This may be applied in one application in fall or winter. On light soils a split application may be desirable, one-half of the fertilizer being applied in late winter and the remainder in spring. Excessive or late applications of nitrogen may delay fruit maturity and color. Some evidence indicates that excessive nitrogen applications cause increased vegetative growth and reduce fruit production.
There is not evidence to show that phosphorous (P) or potassium (K) will improve growth or fruit quality when used to fertilize pomegranate orchards. Occasionally, zinc deficiency is evident in trees. This is corrected by applying zinc sprays during the dormant season or to the foliage in spring and early summer.
Irrigation
The pomegranate can withstand long periods of drought. Although not much fruit is produced under drought conditions, trees will survive for years; then, if properly irrigated, they grow vigorously and produce good crops.
Trees will thrive and produce an abundance of fruit under high summer rainfall conditions but the fruit tends to be soft and has poor shipping and storage quality.
To produce large crops of good-quality fruit, pomegranates require about the same amount of water and frequency of application as citrus. Adequate soil moisture must be maintained throughout the growing season, particularly as harvest approaches in late summer and early fall, when it helps reduce the number of split fruit.
Most orchards are irrigated under the furrow system, but sprinkler and drip irrigation systems are satisfactory if properly designed. Orchards thrive under noncultivation and semi-noncultivation systems. Weed control is difficult because at present no pre-emergence herbicides are registered for use in pomegranate orchards.
Harvesting and Yield
The fruits ripen 6 to 7 months after flowering. The fruit cannot be ripened off the tree even with ethylene treatment. Growers generally consider the fruit ready for harvest if it makes a metallic sound when tapped. The fruit must be picked before over maturity when it tends to crack open if rained upon or under certain conditions of atmospheric humidity, dehydration by winds, or insufficient irrigation. Of course, one might assume that ultimate splitting is the natural means of seed release and dispersal.
The fruits should not be pulled off but clipped close to the base so as to leave no stem to cause damage in handling and shipping. Appearance is important, too much sun exposure causes sunscald–brown, russeted blemishes and roughening of the rind.
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