Concepts and Principles of Grafting

Concepts and Principles of Grafting

Grafting is a technique used to untie ‘parts’ of different plants by bringing the cambium of each into contact to grow together as one plant. The technique involves two important stages: the preparation of the grafting surfaces and the procedures for aftercare. The advantages of grafting include:

  • Reduced height for easy picking
  • Good quality fruit from selected varieties
  • Early fruiting after only a few years.

There are several types of grafting namely: cleft, side-veneer, bark, splice, whip, tongue, saddle and approach grafting. One of the simplest and most popular forms of grafting is described in this module. It is known as cleft grafting.

Raising Rootstocks

Allow a single stem to grow for 6 to18 months depending on the species. The technique involves formation of a union between scions taken from desirable mother trees and rootstocks that are normally young or healthy seedlings established in the nursery. If grafting is done with the right plant material, it can shorten the period between field establishment and when a tree flowers and fruits. This is important for fruit trees, since early maturity means revenues can be realised more quickly by farmers.

To achieve a successful graft, it is important to have healthy, actively growing rootstocks which grow well in your area, as well as scions with active (swollen) buds that have not yet opened. Normally, scions and rootstocks should be of the same diameter, in order to align cambium layers. This is required for the formation of the graft union, to allow the effective movement of the nutrients and water needed for plant growth between roots and shoots.

Selecting and Handling Scion

The best quality scion usually comes from shoots grown the previous season. Scions should be severed with sharp, clean secateurs or knives and placed immediately in moistened plastic bags or tissue papers. It is a good practice during the harvesting of scions and the making of grafts to clean the cutting tools regularly. This may be done by immersing them in a sterilizing solution such as alcohol or methylated spirit. An alternative sterilizing solution may be prepared by mixing one part household bleach with nine parts water (by volume). However, this bleach solution can be highly corrosive to certain metals.

For best results, harvest only as much scion as can be used for grafting during the same day. Select only healthy scion that is free from insects, disease or damage. Be sure the stock plants are of good quality, healthy and true to type. If large quantities of scion wood must be harvested at one time, follow these steps:

  • Cut all scions to a uniform length, keep their basal ends together, and tie them in bundles of known quantity (for example, 50 scions per bundle).
  • Label them, recording the cultivar, date of harvest, and location of the stock plant.
  • Wrap the base of the bundles in moistened tissue paper or cotton wool, place them in polythene bags and seal the bags.
  • Store the bundles for short periods, if necessary cool box.

It should be noted that grafting, as well as budding, the vascular cambium of the scion or bud must be aligned with the vascular cambium of rootstock. In woody plants the cambium is a very thin ribbon of actively dividing cells located just below the bark. The cambium produces conductive tissue for the actively growing plant. This vascular cambium initiates callus tissue at the graft or bud unions to stimulate tissue growth and healing.

How to do cleft grafting

  • Harvest scions from the desired mother tree and cut them about 15cm long. Remove all the leaves carefully. The scions should be the same thickness as the rootstock stem.
  • With a very sharp knife cut the bottom of the scions with two sloping cuts 3½cm long (A)
  • Cut off the top of the rootstock about 30cm above the soil. Make one straight cut about 3cm deep in the top of the rootstock (B) to form a wedge.
Top cleft grafting method

Activity

Grafting techniques

In this trial you will try several types of grafting techniques to understand the advantages of each method.

Procedure

  • Prepare grafting tools and bring root stock and scion.
  • Select two types of grafting techniques and graft 5 seedlings each using same techniques (graft one inch higher than usual height so it could be grafted again in case grafting is not successful).
  • Push the scions firmly into the rootstock cut. Leave ½cm of the cut scions outside the rootstock as shown.
  • Use clear plastic tape to wrap firmly around the graft. Do not remove the tape until the scion begins to grow – showing the graft has been successful.
  • Remove any buds which have grown below the graft. If the graft dies, you must allow one bud to grow below the graft and wait several months before trying again.
  • Observe daily and count the number of success.
  • Re-graft the unsuccessful seedlings
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