Rootstocks

What Is A Rootstock?

A rootstock is just what it sounds like, an established healthy root system. Rootstocks provide the root system that the chosen scion variety is grafted on to.

Why Use A Rootstock?

While the scion determines the variety of fruit a tree will produce, the rootstock determines the size, vigour, disease resistance, the type of soil conditions it can handle, and to an extent the longevity of the tree.

Also, fruit trees grown on commercial rootstocks tend to produce trees that fruit within a year or two, rather than having to wait the 3-8 years it takes to get fruit from a tree grown from seed. Fruit grown from seed does not necessarily produce the fruit the same as the parent.

It should be noted that generally the more dwarfing a rootstock, the shorter the lifespan of the tree will be. For instance pear trees on pear rootstock can live for over 300 years. For example the Kerikeri Pear tree which is over 200 years old. However pears on quince rootstock have a general life expectancy of around 40 years.

The Potted Pear's Grafting

We graft all our trees high on the rootstock, 20-30cm above the ground level. Most nurseries only graft 5cm above ground level. The graft union must be kept above above ground, so grafting higher it means that you can plant the tree deeper, providing more stability, which is good for more dwarfing rootstocks. Because rootstock will often continue to develop roots when the base of the tree is mulched or heavily shaded, having the graft higher off the ground means you can have mulch around the tree.

We currently use MM106 and M26 for our apples, and Bartlett pear seedlings for our pears.

You might wonder why we do not use more dwarfing rootstocks for our espaliers. The reason is that espaliers are not dwarf trees. They are trees that have been kept small by the use of pruning and training techniques. When you train espaliers, especially in a horizontal style, it requires more effort for the tree to pump sap up from the roots to the leaves, and this naturally keeps the tree smaller. Rootstocks such as M26, M9, and M27 lack the vigour to pump sap in an espaliered tree, unless it is in the single cordon or step over style.

General Information on Rootstocks

APPLES

M793

Approximate Size: 90%

Resistance: Woolly aphid, some tolerance to phytophthora.

Growing conditions: Suitable for clay soils

Advantages: Adapted to a wide range of soil types. Produces trees that crop earlier and heavier than Northern Spy.

Disadvantages: Grows into a very tall tree.

Northern Spy

Approximate Size: 75%

Resistance: Woolly aphid, some tolerance to phytophthora.

Growing conditions: Heavy or clay

Advantages: A hardy rootstock which is adapted to a wide variety of soil types yet producing good quality and yields of fruit. Moderately precocious

Disadvantages: Grows into a very tall tree.

MM106

Approximate Size: 70%

Resistance: Woolly aphid.

Growing conditions: Good on most soils, except poorly drained sites.

Advantages: The best rootstock for most garden and small orchard situations, particularly when grown on good soils and well watered. Useful for both free-standing trees and for large fans and espaliers. Does not need staking, and can be left to its own devices once established.

Disadvantages: Whilst much of the crop should be accessible from ground level, you may need a ladder to pick fruit from higher up the tree.

MM102

Approximate Size: 50-55%

Resistance: Woolly aphid.

Growing conditions: Good on most soils, except poorly drained sites.

Advantages: Precocious (meaning it begins fruiting at an early age). Branches will need support when young to handle weight of the fruit. Generally easy to grow.

Disadvantages: Susceptible to collar rot on wet sites

M26

Approximate Size: 40-45%

Resistance: No outstanding resistances.

Growing conditions: Average soils including grassed orchards

Advantages: Produces a good productive tree. Good choice for cordons. One of the most cold-hardy of the Malling-series rootstocks.

Disadvantages: Usually needs a permanent stake, but this need not be as prominent as it is for the smaller rootstocks. Susceptible to fireblight and woolly aphid. Some authorities classify it as susceptible to collar rot (which is an issue if planting in damp ground).

M9

Approximate Size: 25-30%

Resistance: Phytophthora

Growing conditions: Suits well drained, fertile soils. Not suitable for heavy clay soils.

Advantages: Although M9 induces a small dwarf tree, the apples are usually slightly larger than for the same variety on other rootstocks. The tree will bear fruit at a young age, you should get a few apples in the 2nd or 3rd year.

Disadvantages: Requires a permanent stake. The ground around the tree should be mulched or kept weed free, because it cannot compete with other plants. Not suitable for areas where fireblight is prevalent.

M27

Approximate Size: 15-20%

Resistance: No outstanding resistances, some tolerance to phytophthora.

Growing conditions: Good weed and grass free soil. Water plants during drought. Unsuitable on poor soil and for weak cultivars

Advantages: Produces a very small apple tree, reaches its mature size within 2-3 years. Allows you to grow several different apple varieties in a relatively small space. Very easy to manage because everything is within easy reach. Useful for growing in patio containers.

Disadvantages: Needs a permanent stake. Requires regular watering and good soil conditions. Mulch or clear the soil around the tree - do not allow competing plants to get near.

PEARS

Three species are used as rootstock for pears - Cydonia Oblonga (a.k.a. Quince), Pyrus Calleryana, and Pyrus Communis (a.k.a. the European Pear). Pyrus betulaefolia is often used overseas as Nashi rootstock. A list of pear varieties compatible and incompatible with quince can be found at orchardpeople.com. Some sources say that Crataegus Oxyacantha (a.k.a. Hawthorn) and Sorbus Aucuparia (a.k.a. Mountain Ash) can also be used successfully. Pear can also be grafted onto some Malus Domestica (a.k.a. Apple) varieties (but not Apple on to Pear). Winter Banana is a known variety that is compatible with pear.

Quince-C

Approximate Size: 30-35%

Resistance: Crown gall, pear decline, nematodes, root aphids, mildew.

Growing conditions: Fertile, moisture retentive soil.

Advantages: Very productive and precocious (meaning it begins fruiting at an early age). Little suckering. Produces a small tree.

Disadvantages: Some incompatibilities, notably Bartlett (WBC), Beurre Bosc, Clapp's Favourite and delayed in compatibility with Packham's Triumph. Generally trees are interstemmed with Doyenne Du Comice or Beurre Hardy. Requires permanent staking.

Quince-BA29-C

Approximate Size: 50-65%

Resistance: Pear decline, crown gall, nematodes, root aphids .

Growing conditions: Fertile, moisture retentive soil. More cold tolerant than Quince C

Advantages: Produces a high yielding tree

Some suckering can occur.

Bartlett Seedling

Approximate Size: 90-100%

Resistance:

Growing conditions: It can be grown on most soils

Advantages: Compatible with all pear varieties including Asian pears. Trees can be very long lived.

Disadvantages: Trees will grow to over 6 metres.

Pyrus Calleryana

Approximate Size: 90-100%

Resistance: Good disease resistance and compatible with both European and Asian Pears

Growing conditions: Good for warmer climates, adapts well to both sandy and wet soils

Advantages: No interstem required. Trees can be very long lived.

Disadvantages: Trees will grow to over 6 metres.