Hello: I own a small urban farm in Portland as a hobby and am learning as I go. I've got an established Venus grapevine and Himrod grapevine and would love to graft on some grape scions from a friend's grapevine (name unknown). I took a grafting class at HOS many moons ago and remember the basics, but am hoping someone can direct me to an online source specific to grape grafting so I can figure out the timing, techniques, etc. Thanks so much!
My understanding is that grape grafting is kind of a novelty because grapes are one of those things that root and establish easily and quickly. That said it is probably not difficult to graft; possibly top working, or using whip and tongue if sizing is near, likely when sap is just starting to flow, not too heavy. End of Feb, early March I'd guess. Propagation materials collected in dormancy as usual. If you were topworking you'd want to set enough scions to take the sap flow substantially. After they've well established, lose three of the five, keeping the two best positioned. Also removing the other response growth from the trunk thats sure to ensue.
Downsides to grafting grapes would probably be the placing. To keep track of your new variety, especially if your thinking of multiple varieties on one root. Keeping track of what's what with the kind of growth grapes put out could/would quickly get out of hand.
In your maintenance pruning you know you are removing 90% of the previous years growth. Grafting would be somewhat limiting on eventual needs or whims ( I occasionally take out an established cordon and replace it with an well positioned cane for renewal; mostly I spur prune from the cordon, Himrod seems to work ok that way)
The establishing of what ever vine structure you decide to design would be seemingly easier from a new start altogether, rather than default of where you get your 'takes' to establish.
The only really good reason to graft grapes that I've heard of: the European wine grapes were beginning to suffer blight maladies to the point of threatening the wine industry starting in the 1860's. The found fix was to graft to the roots of a wild North American grape, resistance ensued and saved the day. That's what I heard, would make a good case for grafting. Not so much so for changing over varieties, imo.
I searched around and grapes are commonly topworked by stick grafting of scionwood with two buds and the rest of the process is kind of a specialty too. My masters grafting manual states budding is optimized at 80F and it eliminates getting anything accomplished for this year.
The two budded stick method as described in the PDF below needs a one inch stem/stub with a double tongue and two scions on the same stub as added insurance. Make sure you remember to collect your scions and refrigerate them, but I am not even that sure since grapes leaf out so late that's even necessary(?)
Here is the practice as it is performed for California so add about 3 weeks to the dates shown;
Side whip grafting of Grapes
Because grapes are not so easy, one last note is that when selections of scionwoods are specified as having more than one bud is usually because the extra one is important in the aid of enough callus healing to happen at the graft.
The fact that the OP says she has a hobby farm, makes me think the likely motivation for the request is to add some grape varieties rather than to save space.
So rooting some cuttings to make new plants, which is what's typically done for table grapes here is probably the way to go.
I think the grafting is for hard to root vinifera grapes, or where special disease resistance is required.
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