Hard Graft

Working with the London Orchard Project, the London Borough of Sutton’s Biodiversity Team and the Sutton Nature Conservation Volunteers yesterday held a fruit tree grafting workshop at Carshalton Road Pastures nature reserve. People from around London gathered to learn from the experts how fruit trees are propagated.

The generation of fruit trees via their seeds is a very hit and miss affair; the natural variation based on sexual crossing (the admixture of male and female genetic material at fertilisation), as with all sexual congress, introduces a variety of mutation, in the way that all children are different from their parents. To preserve breed fidelity (i.e. ensuring a particular apple species, say, remains ‘that’ apple species), the adult growth is cut and added to a different species’ ‘rootstock’. In botany, plant species of wide ranging parentage can be crossed to create a fertile hybrid, unlike the vast majority of the animal kingdom. Thus, an apple of genus Malus can be added to a hawthorn (genus Crateagus) shrub and the two will incorporate some of the characteristics of the two. This doesn’t necessarily mean one will produce a ‘thorny apple’, there are a far wider ranging set of characteristics that can be inherited, such as resistance to drought or amount of fruit produced. The real secret of grafting though is the fidelity to the initial stock. Thus, a Cox’s Pippin apple, if planted as a seed, will produce something akin to a Cox’s Pippin. The seed of the ‘akin to a Cox’s Pippin’ will be slightly different still and so on, until something that isn’t a ‘Cox’s Pippin’ is produced. If you want to produce a Cox’s Pippin, you need to take some ‘pure’ Cox’s Pippin and graft it to something that will act, essentially, as a ‘host’ to that ‘pure’ stem’. Thus, the rootstock will provide the nutrients to the graft (technically, the ‘scion’), which will take those nutrients to produce the Cox’s Pippin variety.

Much as wounds in humans need a certain amount of care, one cannot cut, willy nilly, into two trees and expect them to survive. Consultant arboriculturalist to the London Orchard Project, Russell Miller, demonstrated two common grafting techniques. The first in known as ‘rind grafting’ or ‘crown grafting’. This takes two stems (one from the rootstock and one from the scion) of different diameters and fuses one to the other. The key is to create a contact between the growing parts of the rootstock and the scion. The growth of woody species occurs in two places, the bark cambium and the vascular cambium. Both of these areas create matter through cell division, although the main purpose of the bark cambium is to produce bark and as such, is less integral to the propagation of the scion than is vascular cambium. The contact between the vascular cambium of the rootstock and the scion is absolutely vital to successful growth.

When rind grafting, one tops (cuts off) a particular branch of the rootstock, creating a neat transverse cut. Then, using a grafting knife, one makes a small vertical incision into a face of the rootstock. The aim is to cut about ½ inch down the rootstock and peel back the bark and bark cambium in a neat slit. The scion, which is of a much smaller diameter than the rootstock, is cut at an oblique angle to produce an angled face, which has a relatively greater amount of surface area than a transversely cut branch. The scion, which is precut to have four buds only, is then slid into the slit on the rootstock, so that there is cambium to cambium contact. Once the contact is made, the wound needs sealing to prevent desiccation (drying out) of the scion and to prevent infection. First, a polyethylene tape is wound around the graft to restrict movement and to reduce desiccation and then grafting wax is applied to the scion tip and join to prevent any further aerobic infarction or desiccation.

Members of the workshop grafted a number of apple scions onto a crab apple tree Malus sylvetris, in what is known as family tree grafting (the addition of a variety of scions to one rootstock). We will judge their efforts come autumn when we look to harvest the fruit!

The second technique Russell demonstrated was whip and tongue. In this instance, both the scion and the rootstock have to be the same diameter. An oblique cut is made on each, so that, theoretically, there should be a vascular cambium contact of 100%. Into each oblique cut, a small transverse cut is made, which aids in the bonding between scion and rootstock. Again, grafting tape and then grafting wax are applied to reduce movement and the chances of desiccation and infection.

If you are interested in learning more about fruit tree growing or harvesting, please contact London Orchard Project’s David Blair. If you are interested in wider aspects of biological conservation and the skills therein (habitat management, site management, floral and faunal surveys etc.), please do contact the London Borough of Sutton’s Biodiversity Team at biodiversity@sutton.gov.uk  020 8770 4203 or contact the SNCV at sncvvolunteers@hotmail.co.uk.

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