What is a rootstock and which one should you choose?

What is a rootstock?

A rootstock is a young tree or bush that is cut to remove the aerial parts, onto which a graft will be made. To do this, a notch is made and a scion is implanted onto the rootstock, so that they fuse together. What interests us about the rootstock is its root system, while the scion provides the aerial part and will therefore produce the same flowers and fruits as the plant from which it was taken.

When choosing a rootstock, a vigorous plant is selected, one that is suited to the soil and climate, resistant to diseases, with a well-developed root system, etc. It is the rootstock that will nourish the scion and impart its qualities.

Sometimes the rootstock seeks to develop: this is the case, for example, when we see shoots or branches growing below the grafting point. These must be cut, otherwise the rootstock may overpower the scion.

A grafted apple tree, with the swelling of the grafting point visible on the trunk. (photo Adobe Stock)

What is the role of the rootstock?

The rootstock provides the scion with its root system. It allows the scion to feed, to draw water and mineral elements from the soil, and is therefore of great importance for the growth of the plant and fruiting. A good rootstock, for example, optimises the productivity of a fruit tree. Not all rootstocks have the same requirements in terms of soil (pH, moisture, etc.): a wise choice of rootstock allows for the cultivation of a fruit tree or bush suited to the land on which it will be grown. Similarly, the choice of rootstock affects resistance to diseases, pests, and cold.

The main criteria for choosing a rootstock are as follows:

• Compatibility with the scion: the rootstock must be compatible, meaning it should be genetically close to the scion (therefore from the same genus, or at least the same family).
• Soil type: rootstocks have different requirements regarding the nature of the soil (pH, fertility, moisture…)
• Resistance to diseases, pests, cold, and drought: some rootstocks are more resistant than others.
• Speed of fruiting: depending on the type of rootstock used, the young plant will start to bear fruit more or less quickly.
• Vigor: generally, seedling rootstocks produce very vigorous fruit trees with good longevity that grow large in adulthood.
• Adult form of the tree: espalier, low-stem, half-stem, high-stem, or free-standing. For a small garden, one would opt for low to medium vigor rootstocks, which will produce fairly compact fruit trees, while in larger gardens, one can more easily choose vigorous fruit trees that will take on high-stem or free-standing forms.

What are the different rootstocks used and which one should you choose?

Since they will be fused and function together, there must be compatibility between the graft and the rootstock. For this, a rootstock from the same family, or even the same botanical genus, as the grafted plant is chosen. For example, one would not graft a rose onto a citrus tree, or an apple tree onto a walnut tree, as these plants are very distantly related… It is also essential to select a rootstock suitable for the soil and climate. Some varieties are better adapted to calcareous soils than others, for instance.

For roses:

• Dog roses (Rosa canina): Roses are often grafted onto dog roses. These have the advantage of being well-suited to calcareous soils, being quite hardy, and fairly drought-resistant.
• Rosa multiflora : Well-suited for roses that will be grown in pots, as the plants become sturdy and branched, with a flexible root system. It tolerates acidic soils and does not like calcareous soil (it risks developing chlorosis in calcareous soil).
• Rosa laxa: Suitable for calcareous soils.

For citrus trees:

• Poncirus trifoliata: This is the bush most often used for grafting citrus trees. It has the advantage of being quite hardy. However, it should be noted that it does not tolerate calcareous soil but is well-suited to acidic terrains.
• Seville orange (Citrus aurantium): It is quite vigorous and particularly suitable for lemon trees and calcareous soils. However, it is sensitive to heavy and wet soils.
• Citrus volkameriana: It is very vigorous, tolerates calcareous soil, and is hardy down to -7 °C.
• Citrange Carrizo: Quick fruiting and good productivity.

Grafting a cherry tree and an apple tree

For apple trees:

The varieties used as rootstocks for apple trees are generally clones, obtained through vegetative multiplication, and designated by the letter M followed by a number.

• M2 (Doucin de Fontenay): This is a vigorous rootstock, suitable for low-stem, goblet, and palmette forms. Fruiting occurs after 5 to 6 years. It is not demanding regarding soil quality, tolerates dry and poor soils, and copes well with calcareous conditions. However, it is sensitive to woolly aphids.
• M9 (Paradis jaune de Metz): It is suitable for compact forms, either low-stem or espalier. It thrives in ordinary soil, not too dry or too wet. Good productivity and quick fruiting (2 to 4 years). It tends to sucker.
• M26: Slightly larger and more vigorous than M9, it is particularly suitable for trained forms. Risk of chlorosis in calcareous soil. Sensitive to drought and stagnant moisture. Quick fruiting.
• M106: More vigorous than M26, but it generally produces smaller fruits. Suitable for low, half-stem, and bushy forms. It is sensitive to drought but tolerates calcareous soils.
• M111: For half-stem forms. More vigorous than M106 but less so than the seedling. It is suitable for dry and stony soils but is sensitive to excess lime.
• Seedling apple tree ‘Bittenfelder’: Very vigorous, quite hardy, and not demanding regarding soil type. Suitable for high-stem or free-standing forms. Good longevity but late fruiting.

For pear trees:

• Quince: Allows for compact forms, suitable for small gardens. Fruiting occurs slightly faster than on seedling pear trees. Suitable for heavy and wet soils, non-calcareous. The quinces used can be either Provence quinces or Angers quinces.
• Seedling pear: It has the advantage of being quite vigorous, undemanding, and not very sensitive to calcareous conditions. It is perfect for free-standing forms and has a deep root system. It has a longer lifespan than pear trees grafted onto quince but fruits quite late (3 to 7 years).
• Seedling pear ‘Kirchensaller’: Very vigorous, resistant to cold and drought, but tends to sucker. Late fruiting. It produces slightly smaller fruits than pear trees grafted onto quince.

For cherry trees:

• Wild cherry (Prunus avium): This is a wild cherry tree, spontaneous. It is quite vigorous and thrives in rich, fresh, humus-bearing soil.
• St. Lucie cherry (Prunus mahaleb): It is suitable for dry or calcareous soils. It is important that the soil is well-drained as it is sensitive to stagnant moisture.
• Seedling cherry, Cerasus communis: Quite vigorous, it is suitable for high-stem forms.

Grafting an apple tree (photo Adobe Stock)

For plum trees:

• Myrobalan plum (Prunus cerasifera): The myrobalan plum is a wild plum, native to southeastern Europe and southwestern Asia, which has naturalised in France. Quite vigorous and offering good anchorage, it is particularly suitable for half-stem or high-stem plum trees (free-standing). It is suitable for dry and stony soils and tolerates calcareous conditions. Fruiting is quick, but it tends to produce many suckers.
• St. Julien plum: It tolerates heavy and wet soils. A bit less vigorous than myrobalan, it is well-suited for low-stem and espalier forms.
• Mariana plum: This is a versatile and undemanding rootstock. It does not sucker and is suitable for most varieties, except for the Reine Claude d’Althan.

For peach trees:

• Seedling peach: It is well-suited for deep, non-calcareous soils. Quite vigorous, it is perfect for half-stem and high-stem forms.
• St. Julien plum: Of medium vigor, it is ideal for low-stem and espalier forms. It is suitable for heavy and wet soils. It is quite hardy and tolerates calcareous conditions.
• Myrobalan plum: It has the advantage of being versatile and well-suited for free-standing forms.

For apricot trees:

• Myrobalan plum (Prunus cerasifera): Undemanding, it is suitable for all types of soil, including dry, wet, or calcareous soils. Suitable for half or high-stem forms.
• St. Julien plum: Suitable for all types of soil, bushy forms, and palmettes. “Plum that tolerates clayey and cool soils. Suitable for grafting of the quenouille as it produces weakly.”
• Prunus persica ‘Rubira’ (seedling peach): For low-stem or half-stem forms. Suitable for poor and well-drained, even sandy soils. Quick fruiting.
• Prunus armeniaca (seedling apricot): Ideal for dry soils, without excess lime. Suitable for dry and poor, stony soils. It is sensitive to stagnant moisture. Vigorous, it is suitable for half-stem or free-standing forms. Late fruiting, but good longevity.

For almond trees:

• Myrobalan plum: Suitable for all types of soil, even dry, poorly drained, or calcareous.
• Seedling peach: For dry soils, but not calcareous. Quick fruiting.
• Seedling almond (Prunus amygdalus): Suitable for dry and calcareous soils.

For quinces:

• Provence quince (BA29): Accepts dry and calcareous soils. Productive, quick fruiting.
• Sydo quince from Angers: Tolerates cold and humidity, but is sensitive to calcareous conditions.
• Seedling quince: For cool and clayey soils, non-calcareous. Quick fruiting and good productivity.

For walnuts:

• Seedling walnut Juglans regia: Suitable for all types of soil, particularly adapted to calcareous terrains. Vigorous, good productivity.
• American seedling walnut: Vigorous, for rich and cool soils. Quick fruiting (about 5 years).