Peach, nectarine, apricot and sweet and sour cherry production are within the genus Prunus. The principles of fertilizer and crop nutrition for high quality fruit production between these species are fairly similar. Where appropriate though, examples of the effects of different nutrients across different species are detailed within the main Nutrient Management section.
Peaches and Nectarines
There are thousands of peach cultivars worldwide, most of which belong to the P. persica species.
Freestone peaches are more widely grown than clingstone peaches. They have flesh that is tender and juicy, which melts upon the bite and which can easily be removed from the stone. They tend to be slightly later maturing than clingstone peaches and are largely sold fresh.
Clingstone peaches have flesh that adheres to the stone. They tend to have firmer textured flesh and so are better suited to canning. Clingstone peaches also retain their shape better and have a brighter colour and clearer juice. Nectarines P. persica. var. nectarina have a ‘hair-less’, smooth skin, and are almost exclusively sold fresh.
White fleshed peaches are more common in China and Japan, but are becoming increasingly cultivated elsewhere alongside nectarines. Yellow-flesh cultivars are more common in the USA and Europe.
The best indication of maturity is background colour. As peaches mature, colour changes from green to straw yellow. Fruit with a fair degree of yellow and sufficient firmness for shipping – around 10psi - as measured by a penetrometer -are ready to be harvested. Total Soluble Solids (TSS) content should also be around 12°Brix. Fruit shape is also used to determine fruit maturity. Fruits that are well rounded along the suture and at the calyx end are ready for picking. Red colouration varies according to cultivar and exposure to light and is thus not a good indication of maturity.
Fresh peaches need to be free of dust, disease and bruises. Skin needs to be intact and well presented with a good bloom. The USA has four standards for fresh peaches. Peaches for canning, freezing or pulping also need to be free of defects. Size can also be a factor, with smaller sized peaches being more difficult to peel prior to canning. The USA has three grades of freestone peaches for processing.
Plums are the most diverse type of stone fruit and are adapted to a very broad range of climatic conditions. They belong to the sub-genus Prunophora that contains over 40 different plum species. Most common are tree plums, either European plums P. domestica or Japanese plums P. salicina.
European plums are taller, more upright, later flowering and maturing. They are oval, smaller and diverse, with different cultivars producing green (greengage), yellow (egg-type), blue and red (Victoriatype) skins. They are mainly blue-red Victoria cultivars – are used for prune production.
Japanese plums are larger, rounder (heartshaped with a pointed calyx) and firmer than European plums. Their flesh is more tightly adhered to the stone. Japanese plums are the most commonly exported fresh plum type and have many varied skin and flesh colours.
P. insititia are smaller fruited types with dwarf rootstocks – they include damsons and St Juliens and are commonly grown for jams, jellies and preserves. P. cerasifera are myrobalan or cherry plums.
Plums for fresh consumption are generally harvested when skin colour and firmness are optimum. However, TSS and TSS/Acid ratios are increasingly being used; sugars should be between 14-17% for export and firmness around 10-20lbs.
Prune production is most common in drier, warmer climates; the crop is particularly sensitive to cracking, even in dry climates and is rarely grown where rainfall is likely at harvest time. European plums grown for prunes are harvested at a more mature stage than fresh plums, when the fruit is starting to decrease in size. They are then dried prior to additional processing. Flesh colour should turn from green-yellow to amber and TSS should be at 25-35%. A firmness of 1-2psi is desirable.
The most common apricot species is P. armeniaca. Other similar species include P. sibirica and P. mandshurica.
P. armeniaca species are most widely grown in mild Mediterranean type climates where summers are warm and dry and the winter and spring is continental. Warm/dry summers reduce disease pressure.
P. mume (also an ornamental form) and P. ansu are the most common species grown in Japan. They perform better in more humid climates and have an astringent or harsh biting quality and are largely used for jams, syrups, pickle and liquor production.
Hybrids of plums and apricots have been recently introduced which have lower chilling requirements and are thus better adapted to warmer regions. Plumcot, aprium and pluot have varying degrees of plum and apricot in their parentage and are said to produce finer fruit. Apricot skin is yellow to orange, often with a reddish blush. The fruit has a prominent suture. Flesh colour is mostly orange, but a few white-fleshed cultivars are grown.
Apricots for fresh fruit are picked ‘firmmature’ for shipping, with harvest suitability based on a measure of fruit firmness, as assessed by using a penetrometer, or the number of days after full bloom. Flesh colour and background skin colour are also key determinants of harvest maturity. Apricots destined for drying are harvested later – when fruit is fully ripe. Canning is a major market as fresh fruit is more perishable than most other Prunus species.
Cherries are a distinctly different type of stone fruit than plums, apricots, and peaches.
Prunus avium is the sweet cherry, and P. cerasus the Sour, Pie, or Tart Cherry. While sweet cherries are solely P. avium species, sour cherry cultivars may include hybrid crosses of P. avium, P. cerasus and P. fruticosa. Sweet cherries include cultivars that produce large dark - almost black – firm fruit for the fresh market, and white fleshed maraschinos or lighter-red fleshed fresh types that are brined or candied.
The fruit is 1.2-3cm in diameter and round or heart shaped with a long pedicle stem. Skin colour ranges from purple-black to deep red and also yellow or white. Sour cherries are typified by Montmorency and the morello-type, Schattenmorelle. They have a rounder, more spreading habit than the erect sweet cherry tree. Sour cherries have lower fruit sugars and higher organic acid contents and are almost exclusively used for processing.
They are generally bright red in colour and produce fruit of the same size as sweet cherries. Pollinator species are needed for sweet cherry production, while sour cherries are self-pollinators. Poor fruit set is more problematic with cherries than other stone fruit.
Sweet cherries for fresh consumption are harvested by hand when they are at the firm-mature stage. Later harvesting would increase risks of bruising. TSS should be around 23% in mature sweet cherries.
Increasingly, producers are assessing the time of harvest when the pull force required to remove the fruit from the pedicle reaches a certain force. Maraschino or glace cherries destined for brining are picked ahead of full ripe colour development – again, force to remove the stem, is often the key determinant for harvest.
Sour cherries – especially those for processing - can be picked later and in some countries are harvested mechanically.