These plum rootstocks are suitable for most European plum varieties, as well as the closely related species of gages, damsons, and mirabelles. There are not as many plum rootstocks as there are for apples, and there are no extremely-dwarfing plum rootstocks.
Krymsk 1 semi-dwarf rootstock
Krymsk 1, also known as VVA-1, is a new dwarfing cold-hardy rootstock for plum trees. It was developed in Russia and released in 2004. It is related to Prunus cerasifera, the Cherry Plum - a species of plums which are naturally quite small.
Plum trees grafted on Krymsk 1 should achieve a mature height in the range 6ft - 10ft or so.
Krymsk 1 also induces precocity, in other words the new tree will start to fruit at a younger age in its life, around 2-3 years instead of the more usual 3-5 years. Fruit size is also improved, compared with some of the more traditional semi-dwarf plum rootstocks.
The main disadvantage is that this rootstock (like most dwarf rootstocks) cannot tolerate drought so will need regular watering over the spring and summer.
Myrobalan vigorous rootstock
Myrobalan is a Prunus cerasifera seedling rootstock, suitable for a wide range of soil conditions. It is usually considered a vigorous or semi-vigorous rootstock, producing a tree with a mature height of 16ft - 20ft.
Trees on Myrobalan should become free-standing but may benefit from staking for the first few years in lighter soils and / or windy situations.
Like most seedling rootstocks Myrobalan is not particularly precocious, and trees should start bearing after 4-5 years.