Plum is temperate in nature and thus a major crop of hills.
It is preferred for planting as a filler fruit plant in mango, litchi and pear orchards due to low chilling requirement and less juvenile period.
Trees are highly productive due to profuse flowering, high fruit set and early ripening habit of cultivars recommended for plains. On an average a full grown tree can yield 50-60 kg of fruit. Plums are rich in sugars and vitamin-A. Fruits are eaten as fresh or processed into jam and squash.
Plum is native to China, although it became a commercial fruit of Japan and America. It is known as Japanese plum due to its cultivation in Japan from where cultivars spread to other places. At present, plum is cultivated in all temperate climate countries of the world.
In northern areas high quality plum is being grown in hilly areas of Gilgit baltistan and Kashmir and Swat. In the plains low chilling requiring plum cultivars are cultivated.
Plum fruit is rich in Vitamin A, B, (Thiamine), riboflavin and some minerals like calcium, phosphorus and iron. The well blended acidity with sugars is helpful in the preparation of jams and squashes.
The dried plums are known as prunes. All plum cultivar cannot be used for drying, that is why it said “all plums are not prunes but all prunes are plums.” The prunes have great Ayurvedic medicinal value. Water prepared from the prunes is helpful in curing jaundice and summer bite.
Prunus salicina belongs to family Rosaceae to which peach and pear belong. Trees are of medium in size in the plains but in hills these are of small size. The bark of twigs and trunk is of blackish-brown in colour, usually shredding from the old scaffolds.
Leaves are oblong oblong and sharply pointed. Leaf margins are serrated, lamina green above and light green on the lower surface. It flowers in first fortnight of February. The flowers are bronze on small spurs with very close rings. Thus flowers occur closely and inflorescence is termed as cymose. Fruit is a drupe (stone) with thin edible exocarp and fleshy mesocarp. The hard stony endocarp contairis seed.
Plum prefers temperate climate. However, it has been found growing from higher hills and areas around Gilgit Baltistan. It requires less chilling hours that is temperature below 7.2°C. It can tolerate frost and high summers both, that is why it can be cultivated in both low temperature to 0°C and up, highest up to 47°C in summers. Some cultivars like Santa Rosa can only be cultivated in higher hills (700-1000 chilling hours) but low chilling requiring cultivators (250-300 chilling hours) are preferred for plains.
Plum is performing very well in soils with high pH where peach fails. That is why it is preferred as filler over peach. For good performance of trees well drained sandy loam to medium loam soils are most suited. Root stock plays a major role in the preference of soil. Own rooted plum cuttings and Kabul Green Gage plum rootstock prefer heavy soils, where as plum propagated on peach do well in sandy loams. Plum propagated on peach should not be planted as filler in Litchi orchards, because of high water requirements of litchi plants.
VARIETIES OF PLUM
Fazle Manani, Stainley, Grand Duke, Gauzales, Formusa, Burbank, Wickson, Methley, Red Beauty, Ruby Red.
Usually plums are propagated through of hard wood cuttings. Varaities are also propagated through hard wood cuttings. Cutting of Kabul Green Gage can also be used for grafting of other plum cultivars. The rooting percentage of cuttings can be increased by dipping the cuttings lower ends for 24 hours in 100 ppm of IB A solution before planting during December.
Dissolve l00mg of IBA in 20ml of absolute alcohol and make the volume one litre. The success of these grafts ranges between 70-80 percent. Though grafts which fail to sprout can be regrafted on to the shoots developed from the rooted cutting next winter. The thickness of cutting should not be more than pencil thickness and length normally 18 to 20cm. simultaneously grafted and rooted cuttings/grafts get ready for planting in the next winter.
Plum stones from the ripe plum fruits are extracted during May. These stones are properly washed to remove pulp and stored after room drying in gunny bags in shade. The seeds are sown in lines in the nursery during November. The seeds are covered with 4-5cm thick layer of sand.
This will be sufficient to stratify the seed in field and seed will start germinating. Alternately the seeds can be stratified in wooden boxes as in peach and kainth seeds. Stratification is complete when the plumule emerges out from the stones of the upper layer of stones in the box.
The emerging seedlings from the stones are gently collected and sown in lines 30cm apart at a distance of 10cm. Leave a gap of 45cm after transplanting four rows: Thereafter light irrigation through flooding should be given. These seedlings get ready for grafting within a year.
Plum plants in the nursery shed their leaves in January. Hence, these are uprooted along with the roots and can be transported long distances bate rooted. While planting the plants in the prepared pits, the lowermost branches should be removed. Keep only 3-4 side branches and clip the tops of all shoots so that secondary branching could be initiated. Place in the small pit all the roots and put soil to cover the roots to the soil level.
Press the soil around the newly planted plants gently. Apply light irrigation to the plants so that soil settles down. Level the soil at ‘wattar’ condition. Continue to apply light and frequent irrigation till rainy season.
Apply 10ml of chloropyriphos in one litre of water to each plant in the root zone 20 days after planting for the control of white ants. The plants getting tilted with first irrigation should be straightened and root zone repressed.
Normally plums are planted as fillers; hence planting distance shall be according to the main fruit crop. This may vary from 3.5 to 5.0 m. However, if pure plum orchard is to be planted, then a spacing of 6m X 6m is enough, which will accommodate 256 plants in square system and 305 in hexagonal system of planting per hectare.
Training and Pruning
Plum trees should be trained according to modified leader system. If healthy plants with some scafforlds selected at the time of planting are planted, the training can be completed in two years. Otherwise, the training is completed in 3 years from planting. The top growing shoot is headed back at planting time at a height of 90cm. The scaffolds selected at a height of 40cm and above are also headed back in January to get branching.
The plants sprout in February and continue to produce sufficient growth during summer until October. One should continue to select side branches during the growing period which will provide a healthy scaffold system within two years. In all, select 4-5 scaffolds all around the trunk.
During the first two years selection of secondary branches on the scaffolds is also carried out. In the third year the top growing leader should be removed from a point of our growing scaffold, during January. Thin out some of the side branches and cris-crossing shoots. The small spurs formed during these years on shoots start flowering. Water shoots sprouting on the main trunk should be removed immediately.
Plums bear on one year old shoots and short spurs depending upon the nature of cultivar. Normally no pruning may be given in the first year of bearing. Remove only cris- crossing shoots and water shoots. Do not too open the tree from inside in the first year of bearing. Remove only cris-crossing shoots and water shoots. Do not too open the tree from in side, let the thin branches have leaves which contribute toward the maturity of other shoots and spurs.
A little pruning to the out growing branches may be done in fifth year onward. The severity of pruning depends upon the planting distance. When plum is planted as filler in pear it may require early severe pruning due to lesser planting distance than in litchi and mango. The cuts may be treated with Bordeaux paste/paint.
Flowering and Fruiting
Flowering in plum cultivars usually take place in the second half of February in the northern plains. Plum flower profusely hence there are sufficient number of hermaphrodite flowers to set fruit. Usually there is very heavy fruit set in plums. However, it is cultivar dependent.
Plum follows a double sigmoid curve of fruit growth. Immature fruits are very acidic. As the fruit mature the acidity start decreasing and TSS goes on increasing. Simultaneously the skin color specific of cultivar start developing.
Plums are shallow rooted and fast growing plants hence need sufficient moisture during growing period. Interval of irrigation may depend upon many factors such as soil type, climate and kind of main fruit trees. Frequent irrigation at weekly interval may be applied during April, May and June. No irrigation at full bloom stage and the ripening stage be given to avoid flower and fruit drop. During rainy season no irrigation is required. The interval may increase to 20 days in September, October and November. There should be no irrigation given during December and January months.
In solid block of plums inter crops can be grown for the first five years. If the plum is planted as filler then there is little space left for growing of crops. Hence inner-crops can only be grown for 1-2 years. The legumes like peas, grams, moong or vegetables should be grown with caution. Water needs of inter¬crops should be such that also favor plum growth and fruiting.
Manures and Fertilizers
Since plum trees grow fast they require nutrition to maintain growth. Plum should be given following doses as per age. Apply farm yard manure, super phosphate and muriate of potash in December. Nitrogenous fertilizer (urea) should be split in to two halves. Apply one half in February and second half in April. In addition the plum trees may be sprayed with a mixture of Zinc Sulphate plus ferrous Sulphate. Both should be of chemical grade. Spray 1 1/2kg zinc Sulphate plus 1 1/2kg ferrous sulphate plus 1 1/2kg un-slaked lime in 500 liters of water during March just when fruits have become pea sized.
In plum orchards several weeds come up. Weeds particularly motha, Khabal grass, baru grass, parthenium and dab are found in abundance. Weeds may be removed from plant basins by hoeing. Weeds from the vacant space may be controlled by spraying Round up (Glyphosate) @ 10 ml/litre and when required particularly during the rainy season.
Thinning of Fruits
Generally plums set fruit much more than it is capable of maturing. Excessive fruit set in plums results in to smaller fruits, which fetch poor price in the market. Thick plants need thinning of fruits to improve in size. Plum should be thinned immediately after natural fruit drop in April. Hand thinning is usually done from top of the shoot to bottom. Fruits are kept at 5-6 cm apart there should be 15-20 leaves for a fruit. There should not be two fruits at one point.
The plum fruits are mature when these have attained proper size and developed proper colour depending upon the cultivar. The plum fruits are harvested from second week of May in Punjab. For local marketing fruits should be harvested when ripe and firm. For distant markets, fruits are picked when firm but have developed 50% colour on the skin. Plum should be harvested along with pedicels avoiding any injury to the fruit.
Plum fruit is very perishable in nature, hence should be handled with care. The small baskets should be padded with rice trash or grass at the bottom and sides. Freshly harvested fruits are transferred in these baskets and covered with paper and tied in gunny cloth.
The fruits should be graded before packing in basket or wooden boxes. Several pickings are made as the entire fruit on a tree do not ripen at one time. Fruit is borne on spurs also so care should be taken to the save the spurs from breakage, during harvesting.