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~ Grape Growing Information ~

Field Grafting to Change Varieties
by Jack Johnston

Many years ago I came across a publication by Dr Keith Kimball, Professor of Viticulture at Cornell, entitled 'Converting Mature Vineyards to Other Varieties', which described a method of grafting cuttings from one grapevine variety onto another. This technique does not require that the old vine be decapitated in the process, so if the graft does not take you can try again next year while continuing to take a crop until the graft is successful. Once the new variety is established, the old one is lopped off.

The beauty of this technique is that if the graft does take, you've got a new variety the next season without having to start from scratch -- ie, you don't have to wait three years to get a crop, and the established root system and the trunk base remain intact.

Since my initial vineyard was planted with varieties I later came to regret, this seemed worth trying. So over the next few years Baco Noir became Merlot, Foch became Cabernet Franc, and Chancellor and Pinot Noir became Pinot Blanc (a few stubborn vines still refuse to take a graft, but little by little...). Dr Kimball indicates an annual 80-90 percent success rate, which I find a little optimistic -- my own has averaged around 50 percent, about the equivalent of most bench grafting.

During this time I have modified Dr Kimball's technique somewhat, and will describe the way I currently do things. This first part will cover the selection of scions (cuttings to be grafted, generally taken during pruning), so that you can work this into your winter pruning schedule.

During pruning, select straight healthy-looking canes from well-exposed areas of the vine whose fruit variety you choose to propagate. One or two (or even more) grafts can be applied to each vine targeted for conversion (hereafter referred to as the 'stock' vine), improving the chances of success. I typically graft two, and sometimes even three, scions onto each stock vine, provided there is room for each on the trunk. So the first step is to determine how many vines you plan to convert and take the appropriate number of cuttings.

Buds on the selected canes should not be too closely or widely spaced, and the cane thickness should be at least 3/8" or slightly larger. Thickness is important because, as will be described later, the scion will be fitted with a plastic tube which, when filled with water, will keep it moist while the graft has a chance to take. 3/8" (inside diameter) plastic tubing works well for this purpose.

Cut segments of two buds each -- 3 if the buds are close together -- with the bottom cut at least 2 inches (preferably 3) below the first bud, and the top cut, at a slant, at least 1 1/2 inches above the top bud (this is where the tube will go). Several scions can be cut from a single cane as long as these requirements are met.

When the cuts are made, check to assure that the inside is green, not brown or grey. Buds should appear healthy and undamaged. Soak the cuttings for several hours in a fungicide solution -- I used to use Benlate, but it is no longer available - chinosol or Topsin work equally well. Then place them in a heavy plastic bag with moist peat moss or spagnum, secure the bag tightly, and store it in the refrigerator until they are ready to be grafted. If you have more than one variety, be sure to keep them separate and clearly labeled.

For the grafting operation, you will need:

  • a razor knife
  • a 1/16" drill bit (plus electric drill, of course)
  • 3/8" (id) plastic tubing - enough for all scions @ 8" each
  • a roll (or rolls) of stem wrap - a stretchy, non-sticky tape that adheres to itself when wrapped
  • 3/4" or 7/8" brads - one for each scion
  • a small hammer
  • 3/4" wide elastic - the kind sold in fabric stores; length depends on number of scions and thicknesses of trunks
  • a staplegun
  • a bucket of water
  • a rubber squeeze bulb with a spout, like those used as ear syringes or for (arggh) giving enemas
  • pruning tar

When should the grafting be done? For this particular method, the window of time is roughly two weeks -- from the time when a small flap cut into the bark of the stock vine will peel back easily ('slip') until bloom. This period is different for each variety and can only be determined by experiment. I generally start checking around the middle of May, since most of my varieties start flowering during the first of June.

For testing purposes, pick a segment of the trunk where the graft will not be made so that you won't waste a potential grafting area. Using the razor knife, make a horizontal cut into the bark (the solid portion, not the loose stuff that you can peel away with your fingers) about an inch wide, followed by two vertical cuts downwards from the ends of this cut. Insert the point of the knife into one corner and pry back the bark. If the flap peels back easily, exposing a smooth whitish-green surface beneath, you're go. If it clings stubbornly or if it's brownish underneath, wait a few days and try again. If you're not sure whether it's working or not, it probably isn't -- you'll know a successful 'peel' when you see it. It might help to practice on some non-stock vine trunks first -- you can't hurt anything.

If the bark peels easily, remove your scions from storage and place them standing up in a bucket of water. Using the razor knife, whittle the bottom of each scion, below the lower bud, into a wedge, first on one side, then the other. One face of the wedge should be about 1 1/4" in length, the other slightly shorter, about 1". The bottom should resemble a fork, with some brownish pith visible between the 'tines'. The buds on the scion should be on either side of the flat surfaces (Fig 1).

Drill a small hole, using the 1/16" bit (you can't very well drill a large hole with this size bit), slightly below the top of the longer wedge face, so that it comes out the other side slightly above the shorter face. Insert a 3/4" or 7/8" brad snugly into the hole in the shorter face (if it slips out easily, use a larger diameter brad) and place the scion back into the water.

Next, cut a number of 8" lengths of 3/8" id plastic tubing equal to the number of scions you have prepared, and slip one on the other end (with the angled cut) of each scion. The fit should be tight (now you know why the diameter of the scions is important, and why this end was cut at an angle). Check for leaks by adding some water to the tube. If the fit is too loose, try wrapping some of the stem wrap around the scion end before putting on the tube.

Find a nice straight area of the stock vine trunk, preferably close to the bottom, and make the horizontal cut into the bark with the razor knife, this time completely girdling the trunk (it goes without saying that the trunk should be of sufficient thickness to avoid the premature removal of the whole top of the vine). Make the two vertical cuts, about 3/4" apart, downward from the horizontal cut a distance of about an inch, forming the flap described earlier. Peel back the bark and use the squeeze bulb to deposit some water behind the flap into the exposed area.

Slip the wedge end of the scion in behind the flap, down as far as it will go (don't force it), and use the small hammer to drive the nail into the trunk, just above the flap, to secure the scion (Fig 2). Be careful not to damage the flap.

Cut a 3" - 4" piece of stem wrap and tuck it in behind the scion -- this will help keep the pruning tar from oozing down between the scion and trunk (Fig 3).

Then cut a longer piece -- the length will depend on the thickness of the trunk -- and wrap it around the graft union several times until it is completely covered. Use the squeeze bulb to fill the plastic tube with water, checking again for leaks (the end of the scion inside the tube will swell a little and tiny leaks may seal themselves). This will maintain moisture in the scions while the graft has time to take (Fig 4).

When no leaks are observed, paint the whole graft area with pruning tar, including the part of the scion below the lower bud, being careful not to get the tar on the bud. Do not allow it to rain until the tar has dried (give it about 24 hours).

After the tar has dried, cut a piece of elastic roughly equal to the circumference of the trunk, and wrap it around the trunk over the taped graft union, stretching it slightly to make a snug fit. Overlap the ends and staple it to the back side of the trunk (Fig 5). The tubes should be checked daily and refilled as necessary, usually for three to four weeks.

During this time, the buds will swell and in most cases put out a shoot, even if the graft does not take. If all goes well, the shoots will continue to grow, often quite rapidly. But don't be discouraged if growth ceases while the shoots are still small -- I've seen graft shoots stop growing after only a few inches but come back vigorously the following year. As long as they produce a bud and keep their leaves during the initial growing season, there's still a chance. If, however, the leaves drop off and the shoots shrivel up, all bets are off. Try again next year -- that's the beauty of this method.

The tubes can be removed any time after the graft has taken, but be careful not to dislodge the graft. I prefer to wait until the end of the season when the scion is firmly adhered to the stock vine trunk. Don't remove the elastic -- it will add support and eventually disintegrate on its own.

Pruning the new shoots during dormancy: depends on the initial growth -- if they grow vigorously during the first summer, I sometimes go ahead and hack off the stock vine, just above the graft, and treat the new shoot as a new trunk extension. If in doubt, cut the new shoots back to a few buds and leave the stock vine intact. You can even take another crop from it the following season, or prune it severely, leaving just enough to recover if the graft runs into problems.

Once in a while, for unaccountable reasons, the grafted portion will take off like gangbusters the second season, only to suddenly wither and die. So don't be too hasty about dispensing with the stock vine -- it's probably best to keep some portion of it throughout the second season, just in case.

The graft shoot itself may try to produce a small crop during the second season. In a few instances, if the shoot is healthy and vigorous, I have allowed it to do so without detrimental effects. Normally, however, I remove the fruit to allow the vine to establish its new growth.

When the older portion of the vine has been removed, you essentially have a new variety, and can take a normal crop from it from then on. I've had a few (out of over a hundred) fail on me after a few years, but it's not clear whether this had anything to do with the grafting. Vines die from any number of causes, and I prefer to believe that these would have bitten the dust anyway. The vast majority have done well and produced good fruit for many years.

Here's hoping yours do likewise.

Maryland Grape Growers Association ©2017