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I have a healthy three year old English walnut. It is about 8 feet tall and 5 feet wide. It was purchased at one of the large home improvement stores (I don't remember which) so the tree itself may actually be grafted onto a black walnut rootstock. I have read that this is common for trees sold commercially.

On a local property there is a 5-year old chance seedling of a black walnut tree growing out of some old farm equipment. The property owner plans to tear out the seedling, but is willing to let me take as much of the tree as I want.

I'd like to convert about one third of the tree to black walnut if possible, but I'm wary of damaging an otherwise healthy tree.

  • How do I graft a branch from the black to the English walnut?
  • Should I attempt large (1/2 in diameter) branches or just smaller twigs/buds?
  • When is the best time of year to perform the graft (I have until next spring)?
  • What type of grafting technique should I use (whip, splice, bark, T-Budding)?
  • Why do you want to do this? Side grafts are unlikely to produce good quality wood stock and this would be a twenty year project. Why not just propagate a cutting? – kevinsky Jun 27 '16 at 16:40
  • @kevinsky I don't have room for a full size black walnut tree. I'm aiming to create a source of both black and English walnuts for edible use. – iAndelin Jun 27 '16 at 17:27
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To begin with, I would collect some small branches/twigs and attempt to root those cuttings. You will probably want pieces that have one or two (compound) leafs and reduce each leaf to about 4 leaflets. The base of the cutting probably ought to be soaked in an IBA (rooting hormone) liquid or dusted with IBA powder of a strength something like 3000 ppm (0.3% IBA) or off-the-shelf RooTone (0.2% NAA). This just serves to kick-start the process of generating roots.

Strike the cuttings in something that is moisture retaining but with a high gas exchange rate, like vermiculite, pearlite, or even orchid moss (sphagnum). I frequently use 1 'gallon' nursery pots - a 1 gallon zip-loc storage bag fits right over it to make a nice humidity tent or terrarium. Clear plastic soda bottles with the bottom cut off works nicely as well. Bottom heat helps if you have something like an old water bed heater that can be set for 75F or so, but it isn't required. Put the covered pot of cuttings in a shady place and wait. Check periodically for fungal problems - spraying a solution of 2 tablespoons of 3% hydrogen peroxide in a quart of water will usually take care of it and it isn't a bad idea to just spray the cuttings every couple of weeks, need it or not. Unless all the leaves (plural of leaf) have dried/rotted, leave the cuttings alone, lest you will break off the newly forming roots. Next spring you will repot your rooted cuttings - just dump them out into a bucket of water as the buds begin to swell or are just cracking. Then pot each rooted cutting separately into a small plastic pot, say 2 or 3 inch diameter (side length if square). You'll need to let them just grow, at least until the middle of next season.

Then you can use them to make approach grafts. You will make a vertical cut on the stock plant wide enough and deep enough to fit the rooted cutting's stem in. Then you secure the pot to the stock, fit the stem in the groove and hold it in the groove with thumb tacks, roofing nails, a padded wire, or a zip tie (this is to hold the stem in the groove for one an maybe two seasons).

Alternatively, you could try bud grafting. You will do this in late winter before buds begin to swell. You begin by cutting a 'T' on the stock and then lift the flaps of bark (if you are too early it will be difficult to lift the flaps - wait a week or so and try again, until you can lift them). Then you will slice a bud off your cutting and slip it under the flaps - do some reading between now and next spring.

With bud grafting it may not be necessary to root cuttings to keep the buds alive until late next winter. Instead, you may be able to store buds on cuttings in a plastic bag with some damp paper/sphagnum kept in your refrigerator until then. It would be best if you can wait until after leaf fall, but your neighbor may not wait. If so, cut the leaves off just below the leaflet pair closest to the stem (the new bud is at the base of this stem where the petiole joins the twig).

Rooting cuttings is your best hope IMHO, and failure is the most likely outcome - it just ain't easy. But go for it!!!

  • This seems like good advice for woody plant propagation. Have you attempted to graft black to English walnut before? What was your success rate? – iAndelin Jun 28 '16 at 15:48
  • Never tried walnut. I am a bonsai enthusiast - walnut leaves don't work out well. Approach or in-arch grafting of a seedling will have the greatest chance of success because both plants are supported by their own roots - you can wait 'forever' for fusion to occur. Side/cleft/bud/etc. grafting is analogous to a cutting. You must keep the scion from desiccating until a connective layer of xylem has grown common to the two. Plus, during the growing season, the phloem sap tends to make the scion be 'spat out' and fail.This is your biggest problem and the reason for the 'plant propagation story'. – Jim Young Jun 28 '16 at 16:45
  • There shouldn't be a 'compatibility' issue with walnut on walnut. UC Davis has a brief review link that is more to the point than my diatribe. – Jim Young Jun 28 '16 at 16:53

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