How to do whip-and-tongue grafting (benchgrafting)

My mom snapped some pictures while I was doing some bench grafts up in Five Islands last visit, so I thought I’d post a photo-lesson on how to do this type of grafts. I’m hardly an expert at this, having just learned last spring, but all seven or so grafts that I made at the MOFGA class last spring took, and then I taught Joshua and Kelsey to do it, and most of the grafts they made took as well, despite the scionwood getting pretty old, so I figure it can’t be that difficult – though it seems that having done a lot of whittling in childhood helps. Some discussion after the photos.

Here’s the scionwood (left), and Budakovski 118 rootstock (right). Normally I use seedling Antonovka rootstock, but Fedco was sold out. B118 makes a tree nearly as large as seedling rootstock, and supposedly comes into bearing a bit sooner than Antonovka. The pieces should be about the same diameter, but it’s not a big deal if the scion is smaller than the rootstock.

Make the first cut at a medium-steep diagonal to the axis of the piece, so as to form a planar face in the neighborhood of 3/4″ or 1″ long, depending on the diameter of the piece. You want to cut it with the unbeveled side of the knife toward the piece you’re keeping, and you want to do it in one smooth motion, rather than whittling away at it, since whittling inevitably leaves a faceted surface rather than a smooth plane. Here’s where my technique is hampered by not having a left handed grafting knife; I basically grip the scion with one hand and freehand the first cut, with the knife pointing away from me:

Getting the first cut smooth, planar, and at the right angle takes some practice; right-handed folks can use a slick technique where the knife is held by the fingers of the right hand (palm down), with the blade over the thumb and pointing back toward the body. The twig is placed between the thumb and the blade and pulled smoothly away from the body, with the angle and pressure on the knife setting the cut at the correct angle. The exact angle doesn’t matter so much as planarity and smoothness. In all cases, avoid touching the cut edges with your fingers (or anything other than a clean knife). Here are the mating surfaces (B118 rootstock has a purplish color, like a redfield):

Place the cuts so they don’t slice through any buds, and flip out any buds that are too close to the graft union and threaten to burst through the wrapping tape prematurely. The next step is to make the axial cuts to form the ‘tongues’ that hold the graft together. This is done with the flat edge of the knife toward the pointy end of the diagonal cut, symmetric across the cut face, and slightly more than half way from the base of the diagonal cut to the tip – I usually make the axial cut at about the pointy end of the central pith, and go until it feels like the twig is about to start splitting ahead of the knife, but hasn’t actually split yet. No material is removed when making this cut, it’s basically just a small controlled split in the twig. It takes a bit of practice to get a clean tongue that’s in the right place and not smashed up:

Once both halves of the graft have both cuts, just push the mating parts together by pressing the diagonal faces together and sliding them axially toward one another until the two tongues engage one another and jam together. If the angles of the diagonal cuts are consistent, and the axial cuts are in the right place, the pieces will fit together so the splice is barely perceptible:

My experience last year is that the fit doesn’t have to be this good to get a strong graft. And if one piece is significantly smaller than the other, don’t split the difference – pick the side where the fit is nicest, and justify the scion over to line up with the rootstock on that side. Here’s one where the axial cuts weren’t far enough toward the tip, so the two pieces go a bit too far past one another – but I’m pretty sure it will take anyway; there’s plenty of good contact between the two pieces:

The graft should be mechanically self-supporting at this point, but it needs to be protected and sealed so it won’t dry out before the union heals together. I use parafilm tape, basically a stretchy and self-adherent but not sticky LDPE film that’s familiar to folks who’ve worked in chemistry labs – Fedco Organic Grower’s Supply sells it. It isn’t UV stable, so it disintegrates at about the right time, a couple months after it’s put out. I start at the bottom (so it sheds water) and stretch it pretty tight as I go (so the faces are pressed tightly together):

If there are any buds in the way of the wrapping, flick them out with the knife so they don’t burst through the tape. Finally, cut the scion off leaving two good buds above the union. One is all you need, but two is good in case one is a dud. More than two and the graft union will have a hard time supporting all that vigorous activity above.

The cut surface at the tip of the scion should be protected with a dab of Tree-Kote or wrapped in parafilm to prevent it drying out. I left the grafted trees in an unheated garage in a bucket of moist sawdust for a couple weeks, until they started showing signs of life up top, then planted them out, though I gather it’s fine to plant them out directly. If the graft takes, the buds will take off and put on at least a foot or two of growth the first summer. Once it’s clear they’ve taken, the weaker of the two buds should be clipped off, as should any buds on the rootstock.

That’s basically all there is to it. Here’s some background info:

Common apple varieties can’t be grown from seed, since the seeds taken from any given type of apple will not produce that same variety of apple if they are sprouted and grown up to maturity. So instead, a little twig or ‘scion’ is taken from the desired type of apple and spliced or ‘grafted’ onto the stem of a small apple tree of a different variety (the ‘rootstock’) , and it grows up to become a full-sized tree with the fruiting properties of the tree from which the scion was taken. While the rootstock can just be a sprouted apple seed (‘seedling rootstock’), in which case it will grow into a robust full-sized tree, in modern practice it is common to graft onto a special rootstock that gives a greater or lesser degree of ‘dwarfing’ character, which means that the tree will not grow as large, but it will come into bearing sooner (though it will be less healthy and be more likely to die after a number of years). Rootstocks can also confer other desirable traits, such as disease resistance. Rootstocks have been carefully selected by various breeding programs, and they themselves must be propagated by special techniques. Dwarfing rootstock is very common in commercial orchards, where economics dictates that the plot must fruit relatively quickly to recoup the capital investment of planting.

So, grafting is necessary to propagate the apple varieties we’re all familiar with. But why not just let a commercial nursery do the work, and buy trees that have already been grafted? For one thing, it’s a lot cheaper; scionwood is free if you have access to a tree of the desired variety to collect from during the March pruning (and the MOFGA scionwood swap is a great source as well), and rootstocks cost from under $1 in volume to maybe $3 for small quantities, while a good quality year-old grafted tree runs over $20 from Fedco. Also, given the dozens of rootstock varieties and hundreds of apple varieties available, it’s simply not practical for nurseries to offer every apple variety on every rootstock, so if the orchardist has a particular need for a particular combination of apple variety and rootstock, custom grafting can be the only way to get it.

The whip-and-tongue ‘benchgraft’ is one common way to splice a scion onto a rootstock. It’s called ‘whip-and-tongue’ because of the shape of the joint that’s made, and it’s called ‘benchgrafting’ because it’s typically done indoors, at the orchardist’s convenience, sometime in mid spring. Typically you’ll start out with a handful of scionwood, and one or more bare-root rootstocks, which will be around 18″ long and somewhere around the diameter of a pencil or less. It’s important to keep the scions labeled with tape or in a labeled bag, since once you lose track of what type they are, they’re pretty much useless. And its important that the scionwood be essentially dormant (i.e. store it in the fridge, tightly wrapped in plastic with moist paper towel or other source of moisture), and its good if the rootstock is somewhat less dormant (I left mine in a 50F basement for a week or so, and the buds had just started to show new growth). The basic idea is to create a splice between the scion and the rootstock that provides a large area for the cambium of the two pieces to touch, and at the same time provides for the two pieces to be held physically together for long enough that they grow together and heal into a strong graft union.

A grafting knife is basically just a single-blade pocket knife with an edge that’s only ground on one side. I bought one (Victorinox) for $20 or so at the MOFGA class. It’s right-handed, and I haven’t bothered to regrind it left-handed, so my technique is a bit awkward, but it seems to work fine. Maybe next year I’ll spring for a nice left handed grafting knife, though the only ones I see readily available online are fancy German ones that cost almost $100.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: