Everything you need to know about plum cultivation, growth and production. Learn about:- 1. Introduction to Plum 2. Species of Plum 3. Climate and Soil Required for Cultivation 4. Planting 5. Training and Pruning 6. Fertilizers and Manure 7. Propagation 8. Harvesting and Postharvest Management 9. Varieties 10. Uses.
Contents:
- Introduction to Plum
- Species of Plum
- Climate and Soil Required for Plum Cultivation
- Planting of Plum
- Training and Pruning of Plum
- Fertilizers and Manure of Plum
- Propagation of Plum
- Harvesting and Postharvest Management of Plum
- Varieties of Plum
- Uses of Plum
1. Introduction to Plum:
Plums are placed within the Prunoideae subfamily of the Rosaceae, which contains all of the stone fruits such as peach, cherry, and apricot. The subgenus Prunophora contains plums and apricots. The common European plum is classified as Prunus domestica, the Japanese plum as Prunus salicina, and the Damson plum as Prunus insititia.
The Japanese plum is native to China, but was domesticated in Japan 400 years ago. It was first brought to California from Japan in 1870 by John Kelsey. In 1885, Luther Burbank imported about 12 seeds from Japan, and used them to breed many cultivars. The plum industry has increased throughout California (mainly in the central San Joaquin Valley) where most Japanese plums in the U.S. are grown.
Two types of plum – European (P. domestica) and Japanese (P. salicina) were introduced during 1870 in Himachal Pradesh and only Japanese plum is being commercially recommended for cultivation in the temperate regions of the north-western Himalayas. Now it is predominantly grown in Himachal Pradesh, Jammu and Kashmir and hills of Uttar Pradesh, and also to some extent in Nilgiri hills of South India.
World (2004 FAO) – 9,836,859 MT or 21.6 billion pounds. Plums are produced commercially in 81 countries on 6.4 million acres. Yields average 3640 lbs/acre worldwide.
2. Species of Plum:
The important plum species are as follows:
1. P. salicina Lindl. (Japanese Plums and Hybrids):
Contrary to the name, this species is originated in China, where it was cultivated for thousands of years. It was brought to Japan 200-400 years ago, where it then spread around the world, being falsely called Japanese plum.
In the USA, it is grown primarily in California, and is the major fresh market plum seen in grocery stores. These are the most common fresh eating plums in the USA. They are larger, rounder (or heart shaped), and firmer than European plums and are primarily grown for fresh market.
2. Prunus domestica L (European Plums):
It grows worldwide and is one of the main species grown. Fruit are generally oval, smaller, and more variable in color than Japanese plums. In the USA, P. domestica is used for prunes or fruit cocktail or other products, and rarely eaten fresh.
3. P. insititia L (Damsons, Bullace plums, St. Juliens, and Mirabelles):
These are the small, wild plums native to Europe, cultivated their prior to the introduction of P. domestica. The ‘St. Julien’ types are used as dwarf rootstocks for plums. Fruit are small and oval (1 inch), purple and clingstone for Damsons and yellow and freestone for Mirabelles, with heavy bloom. They are used primarily for jams/jellies/preserves.
The plant is small to medium sized trees, similar to but more erect growing than peach. European plums are larger and more erect than Japanese plums. Leaves ovate or elliptic with acute or obtuse tips, short petioles, crenulate margins. Japanese plum trees have rougher bark, more persistent spurs, and more numerous flowers than European plums. They are also more precocious, disease resistant, and vigorous than European plums.
Flowers are similar in morphology to peach, but white, smaller, and have longer pedicels. Flowers are borne mostly in umbel-like clusters of 2-3 individuals on short spurs, and solitary or 2-3 in axils of 1-yr-old wood. European plums bloom much later than Japanese types, and are therefore less frost prone. Honey bees are the major pollinator. For Japanese plums, pollinizers are necessary for commercial production for most cultivars. Fruit is a drupe. Oval shaped in European types, round to conical in Japanese types.
Bloom (epicuticular wax) is usually present on glabrous surface (thus, the fruit surface is termed glaucous). Plums require 2.5 to 6 months for fruit development, with most Japanese ripening in relatively short periods (3 months), and some prune & canning cultivars ripening in autumn. Thinning is necessary for proper size development for Japanese plums, but not always necessary for European plums, particularly prunes, since they are not as floriferous, and fruit set is generally lighter.
3. Climate and Soil Required for Growing Plum:
Plums are adapted to a wide range of climatic conditions. Japanese plums are less cold hardy (similar to peach). Plums have chilling requirements ranging from 550-800 hrs for Japanese, and >1000 for European. Rainfall during the growing season can reduce production by accentuating diseases and causing fruit cracking. It is grown from subtropical plains to the temperate high hills. Succeeds in sun or partial shade though it fruits better in a sunny position.
Japanese plums require 700-1,000 hr chilling, which is met in midhill areas located at an elevation of 1,000-16,000 m. Plums bloom early in the season thus they are prone to frost injury. The areas with frost-free spring, having good air drainage and adequate sunshine in summer are most suited for plum cultivation. Plum requires 90-110 cm well-distributed rainfall throughout the year. Prolonged drought and excessive rains during fruit growth and development are harmful.
Plants grow in a well-drained moisture-retentive loamy soil. Prefers some lime in the soil but is likely to become chlorotic if too much lime is present. Soil depth, drainage and pH determine the suitability of soil types. Although plum can grow on a wide range of soils, deep, fertile and well-drained, loamy soil with a pH of 5.5-6.5 is most suitable. The soil should be free from hard pan, waterlogging and excessive salts. Very heavy and light soils are not suitable.
4. Planting of Plum:
Planting distance varies with variety, vigour of rootstock, soil fertility and climatic conditions. Pits of 1m x 1m x 1m size are dug and filled about a month before planting. While digging, the top soil and sub-soil should be kept separately. Pits should be filled first with sub-soil well mixed with 30 kg fully- rotten farmyard manure and filled with top soil mixed with 10-15 kg farmyard manure, 500 g superphosphate and 50 g Aldrin dust.
Planting should be done during December-January. While planting, graft-union should be kept 15-20 cm above the ground level to avoid collar-rot and scion rooting. Proper design of orchard should be prepared before planting which depends on the type of land that is in slope, flat and valley areas. A spacing of plants in row-to-row and plant-to-plant is varieties.
5. Training and Pruning of Plum:
Plum plants are generally trained according to their growth habit and vigour of the rootstock.
Open center pruning is recommended for stone fruit trees and should be done when the tree is 1 to 3 years old. Large branches that fill the center of the tree should be removed. This will leave a “bowl like center”. Be sure to leave enough branches in the center of the tree to provide some leafy growth, which will provide a bit of shade to prevent sunscald. Vigorous upright shoots should also be removed. Light pruning may be done at any time during the year.
Although plum trees are getting ready to crop in early summer, it is important to prune them at this time instead of during the dormant season. Pruning cuts expose the plant to the risk of infection by silver leaf disease; most of the spores of this fungal pathogen are released during wet and cool winter weather. Pruning in summer, when there are not so many spores around, minimizes the risk of the disease entering through the pruning cuts. To further reduce the risk, treat each cut with proprietary wound paint and disinfect pruning tools between trees.
Training is done to give a proper shape and to develop a strong framework of branches. Plum trees are trained to open centre system. The first dormant pruning should be of central leader type. Bearing trees are pruned to maintain a balance between vegetative and reproductive growth.
Thinning cuts that favor (i.e., leave) outward-growing branches are necessary to spread the plum’s upright tree form so that sunlight can penetrate the inner canopy and enhance fruit spur production. After the first growing season, heading cuts should be avoided. Begin dormant pruning after February 1 to reduce bacterial canker infection.
6. Fertilizers and Manure of Plum:
Plum requires adequate amount of nutrients for better growth and quality fruits. Application of manures and fertilizers depends upon soil fertility, type of soil, topography, age of tree, cultural practices and crop load. The requirement of fertilizers varies from region-to-region. Fertilize newly planted plum trees in early spring before leaves appear. Broadcast one cup of 10-10-10 fertilizer over an area 3 feet in diameter.
Apply additional nitrogen in mid-May and mid-July by applying a half-cup of calcium nitrate or ammonium nitrate evenly over an area 2 feet in diameter. Beginning the second year, fertilize the trees twice annually. Make the first application in early March and the second around the first of August.
Use these rules of thumb for the two fertilizer applications:
March application – Apply 1 cup of 10-10-10 for each year of tree age to a maximum of 12 cups for mature trees.
August application – Apply 1 cup of calcium nitrate or ammonium nitrate (equivalent) per tree per year of tree age to a maximum of 6 cups for mature trees.
Always broadcast the fertilizer in a circle at least as large as the circle created by the limbs. Be careful not to concentrate the fertilizer near the trunk of the tree.
Soil analysis and leaf is generally necessary to decide the schedule for fertilizers and manures. The schedule used for plum orchard in Himachal Pradesh is given in Table 30.4.
Boron deficiency results in misshapen fruits. Spray of 0.1% boric acid (0.1%) in June is recommended.
Aftercare:
Floor management of plum orchard is essential. Clean basin + permanent sod may be used. The basins should be weed free while the rest of the orchard floor is kept under permanent sod. Mulching of tree basins is done with 10-15 cm thick hay in March. Besides controlling weeds, it also helps conserve soil moisture.
Black alkathene mulch is beneficial. Application of Attrazin or Diuron @ 4.0 kg/ha in April as pre-emergence and Gramoxone @ 2 litres/ha or Glyphosate @ 800 ml/ha as post-emergence are recommended. The thinning is essential therefore, foliar spray of 200 ppm Ethephon and 100 ppm Carbaryl at full bloom is recommended.
Week earlier of harvesting by 500 ppm Ethephon spray improves fruit colour, and for fruit size improvement spray of 50 pm Triacontanol after pit- hardening stage is recommended.
Plum requires adequate amount of water throughout the growing season. In India, most of the plum orchards are on sloppy land growing under rainfed conditions. Drought conditions prevail during the fruit growth and development, therefore, irrigation is essential during this period.
7. Propagation of Plum:
Through Seed:
Seeds require 2 – 3 months cold stratification and are best sown in a cold frame as soon as it is ripe. The stored seed are sown in a cold frame as early in the year as possible. The seeds should be Protect the seed from mice etc. The seeds can bear dormancy (slow to germinate), and sometimes take 18 months to germinate.
Prick out the seedlings into individual pots when they are large enough to handle. Grow them on in a greenhouse or cold frame for their first winter and plant them out in late spring or early summer of the following year.
Vegetative Propagation:
Grafting and budding are two common methods used for commercial multiplication of nursery plants, since they do not come true-to-type from seeds. Plum is raised on seeding rootstocks of wild apricot and Myrobalan B plum clonal rootstock. In Punjab for heavy and wet soils, cuttings of Kabul Green Gauge and for sandy loam soil peach seedlings are recommended as rootstock. In India, mass scale propagation techniques of raising clonal rootstocks are not common.
The seedling rootstock is developed using seeds of fully ripe fruits of wild apricot (Zardalu). After drying the seeds are y are treated with Bavisten @ 3 g/kg. They are stored at 3.3° – 7.2°C with a RH of 20%. The dormancy is removed after stratification in moist sand for 45-50 days in 30-45 cm deep pits dug in cool and shady place during January. The water-soaked seeds are put in 3-4 cm thick alternate layers of sand and kept moist during stratification. In severe winter affected regions the seeds are sown directly in nursery beds in December or January.
In nursery, the stratified seeds are sown in beds (6-10 cm deep) in rows (25 – 30 cm apart) with a distance of 10-15 cm. The nursery beds are then covered with 10 cm thick hay mulch. Mulching will protect the seedlings from direct sun, heavy rains and spring frost. Light irrigation should be given after sowing. This will avoid desiccation of stratified seeds. When seedlings attain the height of 5 cm the hay mulch is removed followed by regular irrigation and weeding. Single stem should be allowed to grow and remaining side shoots are pruned off.
When the seedlings attain the age of 12 months (about 90%), are used for grafting. For this purpose Myrobalan B is recommended for raising plum plaints. It is multiplied through mound layering (stooling). The rooted layers of the clone are planted in well-prepared stolbeds in December keeping a distance of 30 cm in rows and 60 cm apart. Numerous suckers will come out from layers, therefore, they should be covered by 2-3 soil mounding.
The suckers are ringed near the base during rainy season and treated with 750 ppm IBA for quick and better root initiation. The rooted layers are separated in December and lined out in nursery beds for further grafting.
Hardwood cuttings of Myrobalan B may also be used for propagation. A treatment of IBA (2,500 ppm for 10 seconds) should be given. These cuttings are planted to open field during January-February.
Seedlings as well as clonal rootstocks (0.8-1.2 cm thickness) are grafted in February. The scion should be collected from bearing, disease-free trees of known pedigree during dormancy. Generally, 1-year old shoots having only vegetative buds and smooth growth are preferred.
Tongue grafting in February is most commonly used and ideal method of propagation.
Chip budding during mid-February also gives good success. T-budding during July-August is also recommended but the plant growth is slow and takes 2 years to attain standard-sized plants. In Punjab, own-rooted plants of Kala Amritsari are generally used for planting.
8. Harvesting and Postharvest Management of Plum:
Varieties of indices are used for plum maturity, depending on use, species/cultivar and location. Since plum is a climacteric fruit, it does not attain fully ripe, edible quality on tree. Plum fruits should, therefore, be picked at proper stage.
Picking of immature fruits results in poor quality plums lacking flavour and taste. They shrivel during transpiration and storage. Various maturity indices – days from full bloom, firmness, TSS, change of ground colour from green to yellow or red depending on cultivar – used to judge proper maturity of plums.
Japanese plums and European plums for fresh market are harvested based on skin color and firmness, although sugar content and sugar to acid ratio has been used. Flesh color, firmness, and sugar content are the most reliable indicators for harvesting. A color chip guide is used to determine maturity for some cultivars. Firmness, measured by squeezing fruit in the palm of the hand (spring), is also a useful maturity index for a few cultivars.
Measurement of fruit firmness is recommended for plum cultivars where skin ground color is masked by full red or dark color development before maturation. Flesh firmness, measured using a penetrometer (8-mm tip), can be used to determine a maximum maturity index, which is the stage at which fruit can be harvested without suffering bruising damage during postharvest handling. Plums are less susceptible to bruising than most peach and nectarine cultivars at comparable firmness.
Plums for fresh consumption must be hand harvested, and require 2-4 pickings for optimal maturity over a 7-10 day period, as for peach. Prunes for canning or drying are harvested by shake and catch methods like sour cherries. Fresh prunes are picked on the basis of color, i.e., at least 50% of the fruit surface is red or purple.
Generally 2 pickings are recommended for plums, since all the fruits do not mature evenly on trees, at one stage. Fruits are picked without pedicel in such a way that bruising and stem punctures are avoided. After picking they are put softly in picking baskets lined with gunny cloth and transported to grading and packing house.
Fresh plums are handled postharvest just like peaches. Prunes used to be dried in the sun like raisins, but now are dried in forced air tunnels for a more uniform product.
Fully grown plum trees yield 60-70 kg fruits. Harvesting time varies from variety-to-variety in different states. These are available in the market from second week of May (Titron) to third week of July (Jamuni).
Plums are graded according to their fruit size in 3 grades. Fruits are packed in layers in the wooden boxes of 37 cm x 16.5 cm x 16.5 cm size. Firstly boxes are lined with paper and then fruits are packed in layers with each layer lined with paper to protect the fruits from bruising during transportation.
Postharvest life varies among cultivars and it is strongly affected by temperature management. Most plum and fresh prune cultivars are susceptible to chilling injury when stored at 5 °C (41 °F). In all plum cultivars, a much longer market-life was achieved when stored at 0 °C (32 °F) than at 5 °C (41 °F).
Although plums are highly perishable, they can be stored for 2-4 weeks at 0°C with 85-90% relative humidity. Dipping plums in 4% calcium chloride for 2 minutes increases their storability without any reduction in loss of flesh firmness for 12 days at room temperature.
Plums have similar storage characteristics and problems as peaches, cherries, and apricots. They can be stored about 2-3 weeks at 32° F and 90% RH. Neither species is susceptible to chilling injury in normal storage conditions. Brown rot and Rhizopus rot, and blue and grey molds are the most common storage problems.
9. Varieties of Plum:
There are about 280 varieties of plum available in the country. A few of them are being grown commercially. Most of the varieties grown in India belong to Japanese group. However, in dry temperate zone of Himachal Pradesh, prunes are also grown.
A large number of cultivars (283) have been introduced into the country. European plums performed better in the hills, while Japanese plums are more adopted in sub-mountainous lower elevations. Leading cultivar in the hills is Santa Rosa. In the north-Indian plains small fruited cultivars like Titron, Kala Amritsari, Kelsey, and Alubukhara showed better performance. A good number of low-chilling Florida hybrids (Fla-1-2, Fla 73-4, Fla 85-2, 85-3, Fla 86-4) Sungold, Redgold etc. are under evaluation.
Once prunes are dried, they are relatively resistant to postharvest diseases, and can last for months. Plums can be ripened by placing them in a paper bag, closing it loosely, and leaving it on the counter for a few days. Once the fruit is ripe, it should be stored in the refrigerator for up to three days.
10. Uses of Plum:
i. Food:
Fruits has a unique taste, sweet and juicy. They can be eaten out of hand, made into pies, preserves etc. or be dried for later use. The fruit is very resistant to rotting. The plum-shaped fruit is up to 7 cm long and contains one large seed.
Most Japanese plums are marketed as fresh fruit. European plums have a much wider variety of uses. In California, almost all European plums are dried for prunes. In other plum producing states, utilization is reported as – 30-50% fresh, 18-25% dried (prunes), 20-25% canned, 1-3% frozen.
Plums are used for jelly/jam/preserves, brandy and cognac, pies, cakes, tarts, and in confectionery. Per capita consumption of plums is 1.3 lbs. The fruits are low fat, saturated fat-free, sodium-free, cholesterol-free, and contain high level of vitamin C.
Dietary value, per 100 gram edible portion:
ii. Medicinal:
The fruit is stomachic. It is said to be good for allaying thirst and is given in the treatment of arthritis. Although no specific mention has been seen for this species, all members of the genus contain amygdalin and prunasin, substances which break down in water to form hydrocyanic acid (cyanide or prussic acid). In small amounts this exceedingly poisonous compound stimulates respiration, improves digestion and gives a sense of well- being.
iii. Other Uses:
A green dye can be obtained from the leaves and a dark grey to green dye can be obtained from the fruit.