Lab I. Top Wedge Grafting

For information about the use and commercial applications of Top Wedge Grafting, including links to several Web sites which describe it in detail, go to Top Wedge Grafting  under the List of Grafting and Budding Methods.

B. Top Wedge Grafting Exercise Check List

• Before beginning this section, you should read over the Lab Introduction and Overview. Then, review the steps involved in Top Wedge grafting below, including the videos.

• Is your knife very sharp? Remember, a dull knife is more dangerous than a sharp one, when it come to grafting. If you need instruction on knife sharpening go to Lab Introduction and Overview.

• Materials:
  • Potted hibiscus plants
  • Grafting knife
  • Budding rubbers
  • Parafilm
  • Twist ties
  • Small plastic bag
  • Water spray bottle

• Choose a hibiscus stock plant with an actively growing shoot tip, that is at least 0.5 cm, but preferably less than 1.0 cm in diameter at the point at which you will cut off the top section and insert a new scion. This graft can be placed at any height along the stem, from approximately ten cm from the top to ten cm from the base. If you are planning to insert one or more T-buds and/or Chip buds on the same plant, the Top Wedge Graft should be placed up towards the top of the main shoot, at least 25 or 30 cm from the base.

2. Cutting the stock plant

• Using pruning shears or grafting knife, remove larger leaves and flowers from the portion of the shoot where you plan to place the scion.
• Make a horizontal, clean cut with your pruning shears, removing at least the top 4 - 6 cm of the shoot, so that the stem diameter across this cut is at least 5 mm (approx 1/4 inch). 
• With a sharp grafting knife, split the understock vertically, down the center, from the horizontal cut to a point approx. 3 - 4 cm down the stem. Depending on the hardness of the wood, a gentle rocking motion of the knife may be useful to start the downward cut.

Passion fruit

• In Uganda, Passion fruit is top wedge grafted to a fusarium resistant rootstock. The top of the rootstock is removed with a horizontal cut. Note minimal stock plant diameter, approx. 0.5 cm.

3. Cutting the scion

After reading through the following steps, view the second video.

• Scion selection: It is possible to cut the scion either from the top of the scion donor plant where the shoot is still green or only partially woody, so that the scion growing point will be the actively growing shoot tip from the scion donor plant. Alternatively, the scion many be cut from a lower, woodier section of the shoot where new growth from the scion will arise from a more or less dormant lateral bud. The former is perferable, since an actively growing terminal scion is more likely to form a successful graft union and new growth from the scion begins sooner. However, the later may be necessary if a terminal scion is not available from your scion donor plant.  
• Cut the scion from the scion donor plant with pruning shears or a sharp grafting knife, in the same way that the top of the stock plant was removed. The scion should be at least 3 cm long to as much as 6 cm long, and include as few as one node in the case of a non terminal scion, or as many as several closely spaced nodes, in the case of the perfered teminal scion. A scion longer that about 6 cm. is more likely to be dislodged (knocked over) later on, and it has a greater surface area for dessication.
• Trim off any leaves from the scion, except very small ones (<1 cm long) at the growing shoot tip.
• Cut the base of the scion into a "V" shape by making two straight tapering cuts about 2 to 3 cm long. A single long cut on each side is preferable to making several passes with the knife to trim the "V", since the former is more likely to be straight and even. The diameter of the scion should be approximately the same as that of the upper, cut end of the stock.

Note: If you are not using the top portion of the stock plant which you just removed to serve as the scion for a different stock plant, it is good to use it to practice making the "V" cut, before proceeding to the real thing.

The scion and understock are first tied firmly in place with a budding rubber to create pressure between the cut surfaces. This is followed by wrapping the union with parafilm to further prevent dessication, and finally the entire scion and upper portion of the stock junction is covered with a plastic bag "tent" to create a humid environment as a third barrier to water loss from the scion.

After reading through the following steps, view the final video.

• The budding rubber is wrapped tightly around the graft, from the base upwards by holding one end of the rubber band against the stock about 1 cm below the graft union, with the thumb of the left hand while wrapping with the right hand. If the scion tends to "pop out" as you tie from the base upwards, try tying from top downwards, to trap the scion in place. To secure the end of the rubber band, the first turn with the right hand should cross over this end, "trapping" under the first turn. The band should be stretched as it is wrapped around the stem to create pressure. Terminate the wrapping about 1 cm above the horizontal top cut of the stock by pulling out a "loop" with the right ,hand and tucking the end of the rubber band through this loop before releasing it and trapping it in place.
• Cut a piece of parafilm about two inches wide and 3 inches long. The paper backing is divided into two inch sections, so cut it along that line. Remove the paper backing, and fold this 2 x 3 inch piece in half long ways so it measures about 1 x 3 inches. To adhere firmly, the parafilm should be stretched slightly before it is wrapped in place. Hold one end of the parafilm just below the bottom end of the budding rubber wrapping, and wrap upwards, just as you did with the budding rubber, until the rubber is entirely covered. Remember to stretch the parafilm as you wrap. At the upper end, fix the parafilm in place so it will not unwrap by running your thumbnail across it, which tends to stick it to the layer of parafilm below it.  
• Create a humidity tent over the graft by placing a small plastic bag upside down over the scion and upper portion of the stock and tie it firmly with a twist tie near the bottom (open end) of the bag, approx. 2 cm below the graft union. Before placing the bag you may wish to lightly spray water inside the bag, with the spray bottle.

Apple

• Top wedge grafting is occasionally practiced in breeding of fruit tree rootstocks. In this case, top wedge grafting is being used to bulk up a rootstock selection (the scions shown here) which is available in limited quantity. Shoots of the rootstock genotype grown from these scions will be layered to get them on their own roots, and then lined out in the field to establish a stool bed for propagation of the rootstock genotype in greater quantities. In this case the top wedge grafted plants are placed in a fog chamber to minimize dessication, rather than covering each with a plastic tent.

Avocado

• In developing countries where budding rubbers and parafilm are not available, the stock and scion are bound together with a strip of polyethylene cut from a plastic bag.

5. Post budding management of the Top Wedge graftted plant

• Place the grafted hibiscus under shade in the greenhouse for several weeks. It is especially important to keep your grafted plant out of the sun since the plastic "tent" which maintains a high humidity around the scion, can over heat very rapidly and kill the sicon.
• Active growth of the scion after one to several weeks is a good sign that the graft is "taking" properly.
• After about 3 weeks cut one or two slits about one inch long, anywhere in the bag so that the humidity will be gradually reduced and the scion will become acclimated to the lower ambient humidity.
• One week later, remove the bag entirely.
• At this point you should inspect the graft union for signs of callusing by removing the parafilm and budding rubber temporarily. A healthy graft union will exhibit a thin line of whitish callus all along the exposed edge of the stock scion junction. At this point, you should tie the stock and scion back together, for several more weeks, before their final removal.