Friday, 15 June 2012

Grapevine grafting (part 1): The graft.

    There are many reasons to graft grapevines.  The main reason, and why grafting vines became common practice, is disease.  To make a long story short, in the mid 8000's, when the vineyards of Europe got infested with phylloxera ( a louse that was unknowingly introduced from contaminated vines that were imported from... America), it was quickly discovered that vines native to America seemed immune to the disease.  So they had two options.  Breeding or grafting. 
      Introducing disease resistance in the European vines by breeding them with American vines was tried and partially succeeded.  I say partially because although the hybrid vines were resistant, they lacked some of the winemaking qualities the original vines had.   One of the side effects of introducing American genes in these hybrids is that the resulting varieties were a lot more cold hardy, enabling us Canadians to grow vines where most European (vinifera) vines would quickly die due to our cold winters.  Most of the modern cold hardy grape breeding programs (University of Minnesota, and Cornell in NY) use these old ''french hybrids'' as a starting point to create new varieties.  There is a lot to say about breeding and hybrids so I will leave the rest for a future post.
     The other option, and the one they quickly chose, was grafting.  By grafting a European shoot (scion) onto an American vine (rootstock), they got the best of both worlds.  The root system of the rootstock was completely immune to phylloxera, and the above ground portion of the vine produced the grapes the winemakers liked.  Most vinifera varieties (Chardonnay and  Merlot, to name a few) are now grown this way around the world. 
    Other interesting effects of grafting are changes in the way vines behave like earlier budding or earlier harvests.  It can also make vines more drought resistant, grow better in different soil conditions.  So there are advantages in grafting vines even though they are disease resistant (like hybrids) to a different rootstock for those reasons.

    So for my grafts,  I chose to use a wild riparia vine as a rootstock.  Those grow like weeds around my vineyard so I thought they would be good candidates. The vinifera varieties I've grafted on the rootstock are Riesling and Chardonnay. 
    And now, the procedure...

    The technique I used is called dormant bench crafting.  Both the rootstock and the scion wood are dormant at this stage.  It seems to be the most common way to graft grapevines.  I tried two variants of this method.  The first is a standard ''omega'' graft where you use a grafting tool to cut the wood into an omega shape so that the joint locks kind of like a jigsaw puzzle.  I bought one of those tools at Lee Valley's for around fifty dollars if I remember correctly.
    I also tried a technique called chip budding where you graft only a bud (chip) from the donor vine onto the rootstock.  This technique is usually used in field grafting, where a dormant bud is grafted onto an actively growing vine in the field.  I couldn't think of a reason why it wouldn't work on a dormant rootstock so I tried it.  My success rate ended up being around 80% with both methods so I figure they are both worth mentioning. 

1)  Omega Grafting.

Tools you'll need.

You will need an omega grafting tool,  painter's tape,  and wax.
You can use grafting wax if you want, I used paraffin wax from a home spa machine that my wife bought and use only once (free wax!), and it worked fine.  The tape is to help secure the graft union.

Cuttings all hydrated and ready to go.
 This is my riparia rootstock.  It was harvested in December and
 kept dormant in my fridge until grafting time.  Cuttings like these can be kept for up to a year provided they are kept moist and cold (0 to 1 Celsius).  I rap them with moist paper towels and seal them in a big Ziploc type bag removing as much air as possible.  You can use your kitchen fridge to store them but try to put them in  the back end of the fridge where it is the coldest.  If you could have a dedicated fridge to store them in,  it would be ideal.  You want to keep the temperature as steady as possible.  I bought a mini-fridge ( on sale for 80 $) which was ideal.   I just set the temperature and left the cuttings in there until I  needed them.  Before you start, weather rooting cuttings or grafting, the wood should be immersed in water for a day or so .  I just put my cuttings in the sink and put a plate on top of them to hold everything under water.  Hydrating them greatly improves the success rate.  Then, just before I start, I dip them in a diluted bleach solution (10 %) for 30 seconds, and then rinse them immediately with plenty of water.  This kills any mold/bacteria that could infect the wounds you'll make when grafting.  Make sure not to soak them in bleach for too long though because it could damage the dormant buds, and the cutting would die.

The next step is to ''debud'' the rootstock.   I used a utility knife (forgot to include in the first picture...) and simply cut the buds off.
Each node contains a bud (three buds actually).  The main bud is easy to see but there is also a secondary and a tertiary bud just under the main one.  These buds normally stay dormant but if something happens to the main bud, they will take over and start growing.  You'll want to make sure to remove them all otherwise, throughout the life of that vine, you will have to deal with removing rootstock suckers that will keep coming every year.

omega cut.
When grafting, one of the most crucial things is to match the size of the wood (rootstock and scion) as closely as possible.  For the graft to be successful, the cambium layers have to be aligned almost perfectly.  The cambium is a thin layer of the wood directly under the ''bark''.  This cambium produces the callus that will weld the graft union into one piece.  Mismatched wood will yield week grafts at best, but will most likely not take.
      Once the buds are removed from the rootstock, I make my first ''omega'' cut on the top of the cutting.  Which reminds me... Cuttings don't grow upside down.   Make sure you are holding them the right way.  The buds usually point up but if you are unsure, there is always a scar directly under each bud.  So next, I make my cut on the bottom of the scion (the grafted part).  It has to be matched to the rootstock so that the graft union ''interlocks'' as in the picture.  Remember that the scion also has an up and a down.

Graft complete.
 Snap the pieces together and wrap tightly with the tape and there it is!  The graft is complete.

    I will switch to chip budding now since it is a variant of this method and get to callusing later.

2) Chip budding.

Tools you'll need.

  Less expensive tools here.  A utility knife with a sharp blade, plumbing Teflon tape, and the same wax.  Proceed the same way as omega grafting for soaking, sterilizing and ''debuding''. 

Chip bud incision.

Instead of making a cut on the top of the rootstock, you make it on the side as in the picture.

Rootstock and chip.
   Next, the goal is to match that incision as closely as possible with the bud.  It takes a little practice to get it right but it's worth it.  Make sure to have some wood to practice with.  To make the ''chip'', I make a first cut at a diagonal starting just under the bud, and slice right through the trunk (cutting the bottom off completely).  All that's left to do is to ''peel'' the bud off with a second cut.  Again, try to match as closely as possible (see picture on the right).

Hold tightly.

Then, push the chip in the incision firmly...

Wrap with Teflon tape.


                       ...and wrap tightly with Teflon tape to secure the bud,

and done! 

p.s. I apologize for the lack of pictures.  I just noticed a lot of them were unusable (bad quality).  I will take better pictures next time and update this post. 

Click here for part 2: Callusing and Rooting

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