Fruit and Nut
Almost all fruit trees and a high proportion of nut trees are grafted - that is, the fruiting part of the tree is grafted onto a separate rootstock. The choice of rootstock determines not just the ultimate size of the tree, but also factors such as disease or pest resistance, tolerance of poor ground or climate extremes, precociousness (ability to begin fruiting early in life), longevity, yield and ability to stand alone without long-term staking.
It is very important, therefore, to choose the right rootstock for the right situation. Amazingly, many garden centres sell fruit trees without providing the buyer with information about the rootstock - this could be compared to a car manufacturer selling a car without any information about engine size or fuel performance!
This page attempts to demystify some of the confusion surrounding rootstocks by listing some of the characteristics of the most common and some less common rootstocks.
These are the most commonly used apple rootstocks in Ireland and the UK:
M25 Very Vigorous
M111 Vigorous, high tolerance of waterlogging
MM106 Semi Vigorous
M116 Slightly less vigorous than MM106, disease resistant
M26 Semi Dwarfing
M27 Ultra Dwarfing
Myrobalan B Very Vigorous
St Julien A Semi Vigorous
Jaspi Semi Vigorous but with greater tolerance of wet situations
Plumina (Ferlenain) Similar vigour to Pixy but improved fruit size.
Pixy Semi Dwarfing
F.12.1 (Mazzard) Very Vigorous
MxM14 Semi Vigorous
Colt Semi Vigorous
Gisela 6 Semi Dwarfing
Gisela 5 Dwarfing
Pear rootstocks (also suitable for quince and medlar)
Pyrus communis Very vigorous
Pyrus Kirchensaller Very vigorous (crops more consistant than Pyrus communis)
Quince BA29 Semi Vigorous (smaller than Pyrodwarf)
Quince A Slightly Vigorous
Quince EMH (Dwarfing but better fruit size than Quince C)
Quince C Dwarfing
The need for staking varies according to the anchorage ability of the rootstock, the degree of exposure to strong winds and the size of the tree at the time of planting. Generally, the more vigorous rootstocks have greater ability to anchor well to the ground. Conversely, trees that are relatively large at the time of planting will tend to be top-heavy and will require more robust staking. Round 75mm x 1.8m fencing stakes make good tree stakes. In exposed locations, heavier stakes may be considered. Lighter stakes, of the kind often sold in garden centres, are unlikely to be strong enough to offer sufficient support. Stakes need to be driven well into the ground. It is better to put in the stake before planting the tree.
It is advisable to cut off the stake approx 100mm above the tying point with the tree as this reduces the likelihood of the tree rubbing against the stake during windy conditions (which causes wounds and increases the risk of diease).
Poles of ash, sycamore, oak or sweet chestnut also make good tree stakes, though ash and sycamore will rot after a few years. Sweet chestnut and oak poles are very rot-resistant and will last longer than any commercial pressure-treated stake of white deal (spruce).
The distances given in the tables should not be taken as absolutes but are indicative. It is always possible to space trees more generously. However, crowding trees too tightly has a number of negative consequences among them the inhibition of tree development (thereby limiting future yields) and the increased risk of disease as orchard ventilation becomes compromised. This is particularly relevant for organic growers (see below).
Disease resistance and tolerance of poor ground conditions
The ratings given are approximate and will vary according to other factors such as local climate and micro-climate, planting densities, and choice of variety. Disease is nearly always more prevailant at higher planting densities. Poor ground (infertile soil; heavy soil; waterlogging) is also a contributary factor in the prevalence of disease.
In the heyday of orchard production in the Nineteenth and early Twentieth centuries, the spraying of trees with toxic chemicals was standard practice. This rather dubious strategy permitted the growing of many disease-prone varieties of fruit that otherwise would have been difficult if not impossible.
Many of these chemicals are now considered a serious danger to health and/or the environment and in a number of cases are outlawed.
The modern organic fruit grower should acknowledge that plant diseases are a fact of life and that the best chance of success lies in appropriate selection of varieties and rootstocks, careful choice of site, good orchard ventilation and general vigilance against unwanted visitors.
Among the fruit varieties that are very disease-prone and thereby unsuited to organic methods are the plum Victoria and the apple Cox's Orange Pippin.
The simplest way to achieve good orchard ventilation is to avoid overcrowding - space the trees generously. Vegetation around the trees should be kept short or suppressed with mulches (but do not pile mulches against the trunk of the tree).
Sweet Chestnut rootstock
While some hybrid varieties of sweet chestnut are propagated by layering or stooling and grown on their own roots, most are grafted onto seed-grown rootstocks of Castanea sativa, Castanea crenata (the Japanese chestnut) or C.sativa x crenata hybrids . The latter offer a good combination of vigour, disease resistance and compatibility with most common chestnut cultivars.
The hybrid Marigoule is often used as rootstock, and produces a tree of good vigour. Other choices include Bournette, Bouch de Betizac, Maraval, Marlhac, Marsol, and Vignois. Trees grown on Marlhac or Vignois rootstocks may leaf out slightly later, which could be an advantage in regions at risk from late frosts.
Walnut cultivars are most commonly grafted onto seed-grown Juglans regia. Occasionally Juglans nigra or Juglans hindsii rootstocks are used. However, walnuts grown on these rootstocks can develop black line, a graft incompatibility that only emerges after 15-20 years.
Rootstocks grown from Juglans regia seed of north-western European provenance are most likely to perform best in Ireland or Britain. The most important nut growing region within this area is the Dordogne in France. Walnuts are also produced commerically (albeit often on a small scale) in many parts of Germany, Alsace-Lorraine (France), southern England and the Netherlands.
Some work has been done on developing dwarfing walnut rootstocks in China, apparently with some degree of success. Although the use of interstitial grafts appears rare in walnuts, there may be scope for using interstices of naturally compact cultivars such as Rita to produce trees of less vigour.
Further sources of information
Martin Crawford of the Agroforestry Research Trust has written a series of excellent directories of apple, pear, cherry, plum, walnut and chestnut cultivars. The directories also contain further information on rootstocks, including details of many rootstocks not commonly found in Ireland or Britain.
Supply of rootstocks for grafting purposes
Many of the roostocks listed above, along with graftwood (scions) and grafting tape, will be available from Fruit and Nut in winter 2012/13, in good time for the next grafting season. The more popular rootstocks sell out quickly so order early to avoid disappointment.