Lab
I. Top Wedge Grafting
Print out
Top Wedge Grafting Flash Card for concise summary of this method.
A.
Background
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
C. Procedure
1. Rootstock preparation.
- 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
After reading through the following steps, view the first video:
NOTE: To
view the videos click on the down-arrow on the bottom-right portion of the player
screen and choose "Open Link."
- 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.
- Insert
the scion into the split upper end of the stock plant by sliding
the tapered ("V") tip of the scion downwards with gentle pressure, until the
top of the "V" cut is even with the top, horizontal surface of the stock.
If both are equal in diameter, the vascular cambia of the scion should be
aligned with that of stock, but if the scion is slightly smaller in diameter
than the stock, the scion should be placed to one side of the stock (rather
than centered), as for cleft grafting, so that the cambia align at least on
one side.
4. Tying and covering the graft
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
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.