Sour Cherry

The Sour Cherry, (Prunus cerasus) is a species of Prunus in the subgenus Cerasus (cherries), native to much of Europe and southwest Asia. It is closely related to the Wild Cherry (P. avium), also known as sweet cherry, but has a fruit which is more acidic, and so is useful primarily for culinary purposes.

The tree is smaller than the Wild Cherry, growing up to 4-10 m tall, and has twiggy branches, whilst the crimson to black fruit is borne on shorter stalks.
Cultivation and uses
Cultivated Sour Cherries were selected from wild specimens of Prunus cerasus and the doubtfully distinct P. acida from around the Caspian and Black Seas, and were known to the Greeks in 300 BC. They were also extremely popular with Persians & the Romans who introduced them into Britain long before the 1st century AD. The fruit remains popular in modern-day Iran.

In Britain, their cultivation was popularised in the 16th century by Henry VIII. They became a popular crop amongst Kentish growers, and by 1640 over two dozen named cultivars were recorded. In the Americas, Massachusetts colonists planted the first sour cherry, 'Kentish Red', when they arrived.
A blooming Sour Cherry tree

Before the Second World War there were more than fifty cultivars of Sour Cherry in cultivation in England; today, however, few are grown commercially, and despite the continuation of named cultivars such as 'Kentish Red', 'Amarelles', 'Griottes' and 'Flemish', only the generic Morello is offered by most nurseries. This is a late-flowering variety, and thus misses more frosts than its sweet counterpart and is therefore a more reliable cropper. The Morello cherry ripens in mid to late summer, towards the end of August in southern England. It is self fertile, and would be a good pollenizer for other varieties if did it not flower so late in the season.

Sour Cherries require similar cultivation conditions to pears, that is, they prefer a rich, well-drained moist soil, although they demand more nitrogen and water than sweet cherries. Trees will do badly if waterlogged, but have greater tolerance of poor drainage than sweet varieties. As with sweet cherries, Morellos are traditionally cultivated by budding onto strong growing rootstocks, which produce trees too large for most gardens, although newer dwarfing rootstocks such as Colt and Gisella are now available. During spring, flowers should be protected, and trees weeded, mulched and sprayed with seaweed solution. This is also the time when any required pruning should be carried out (note that cherries should not be pruned during the dormant winter months). Morello cherry trees fruit on younger wood than sweet varieties, and thus can be pruned harder. They are usually grown as standards, but can be fan trained, cropping well even on cold walls, or grown as low bushes.
Ripe sour cherries, Leamington, Ontario, Canada near Lake Erie

Sour Cherries suffer fewer pests and diseases than sweet cherries, although they are prone to heavy fruit losses from birds. In summer, fruit should be protected with netting. When harvesting fruit, they should be cut from the tree rather than risking damage by pulling the stalks. Morello cherries freeze well and retain their flavour superbly.

Unlike most sweet cherry varieties, Sour Cherries are self fertile (sometimes inaccurately referred to as self pollinating) or self pollenizing. Two implications of this are that seeds generally run true to the cultivar, and that much smaller pollinator populations are needed because pollen only has to be moved within individual flowers. In areas where pollinators are scarce growers find that stocking beehives in orchards improves yields.

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