Types of Plums
There are several different species of plum which produce edible fruit but Prunus domestica, (the European plum) and Prunus salicina (the Japanese plum) are the main types grown. The colour, flavour and texture vary widely between species and cultivars from yellow skinned through to almost black and golden flesh through to the darkest red.
For your trees to actually set fruit, you will need to consider what is called the ‘chill factor’ needed by the variety you want to grow. The chill factor is the amount of hours below 7 °C (over winter) that a variety needs in order to fruit. Plums need between 275 –1200 chill hours below 7°C (depending on the variety). So before you buy your fruit trees ask the grower how many chill hours the variety needs so that you can choose the right variety for your climate.
Japanese plums include the varieties: ‘Santa Rosa’, ‘Satsuma’, ‘Mariposa’ and ‘Ruby Red’ these are one of the most popularly grown plums. Most Japanese plums have less chilling requirements (i.e. they tolerate warmer winters - a chill factor of 300-900 hours below 7°C) and are therefore more suited to warmer areas. Japanese plums, depending on the variety, will bear ripe fruit mostly over summer.
European plums on the other hand need higher chill factor climates and will do very well throughout most cool temperate regions i.e. best with a chill factor of below 3 degrees for 800-1200 hours.
European Varieties include: ‘Victoria’ plum (England’s favourite variety), a self-fertile variety with reddish skin that changes to dark purple when ripe and golden flesh other varieties: ‘Coe’s Golden Drop’, ‘Green Gage’, ‘Damson’, ‘King Billy’. European plums, depending on the variety, bear fruit a bit later than Japanese plums.
Cultivating Plums
Generally plums prefer heavier soils with good water retention properties more than peaches and nectarines where good drainage is more critical.
Although plums seem to fruit irrelevant of whether they are fed or not it does help to look after your trees by giving them an annual application of general fertiliser early spring (preferably organic or slow release such as blood and bone). Some people like to give their plum trees an extra feed of potash - which might be needed in some cases (watch for potash deficiencies, especially in sandy soils, on plum trees this is evident by curling leaves that brown at the edges; don’t overuse nitrogen fertiliser as this can contribute to a potash deficiency.
Pruning Hints:
- Japanese plums tend to bear on laterals (like peaches). Prune these varieties to control growth and stimulate development of new laterals.
- Most plums fruit on either year old wood or older wood but also on spurs but usually most fruit is on two year old wood, so do not remove spurs which are only one year old. European plums tend to bear more on spurs (like apples).
- Fruit thinning is often necessary for Japanese plums and also for the Prune D'Argen variety.
- Unpruned trees are huge producers of fruit and this tends to weigh down the branches and break them.
- The simplest way to prune a plum tree is to remove all growth that is outside of easy reach and leave the rest.
Possible Problems
- Viruses are perhaps the most important problem. You should only use virus free plum stock plants.
- Fungal diseases include brown rot, plum rust, silver leaf (a wood rotting fungus). These are generally less serious on plums than on other fruit trees though. Brown Rot: is another problem associated with plum trees and can be evidenced by sap oozing from the plums and ends of branches and is prevalent in moist, wet and windy weather: prune after harvest instead of winter and burn the affected pruning material and pray with a fungicide for example Eco-Fungicide in winter. (Try Green Harvest for the Eco-Fungicide).
- Bacterial spot: common on plums and evident as a shot-hole appearance on the leaves; plant a less susceptible variety, clean up all diseased material including leaves and old fruit and destroy.
- Insect pests are not commonly a major problem.
- Birds can be a serious problem, and netting may be required.
