Hot Callus Grafting set up for cold conditions

Hello all!
I wanted to just share some details of a new experience hot callus grafting various trees this winter. I originally was inspired by a post on this forum by Dax, where he showed a very simple set up with many using it for great results.
Unfortunately this set up did not work out for me as I only had an unheated root cellar and the temperature was just too cold.
So before giving up, I took the advice of nurseryman Cliff England and set up a more elaborate system that had a built in temp control and have now had my first group of trees come off with near perfect results!

As an overview;

I first cut out notches with a drill and hand saw every 2" down the length of a 2" PVC pipe.
I then did some surgery on an electric heat tape by carefully removing the little button inside the built in thermostat which regulates the temp. WIth that button gone, it will quickly go up to 150+ degrees F. I then wrapped that heat tape around a 1/2" CPVC pipe which I filled up with antifeeeze and capped off the ends. This smaller 1/2" pipe and heat tape were inserted inside the larger pipe with a small strip of cardboard shielding between the hot cable and the trees just in case they touch. The while thing was wrapped up in foam insulation which was then slit with a knife in each space of a notch in the larger PVC pipe within. The heat tape was plugged up to a simple thermostat controller and a sensor placed inside one of the spaces wresting where a tree would.
After placing this on top a layer of roxul rigid board insulation which was laid on the floor of my root cellar, I proceeded to get it up to temp, which was set at a range of 79-83 degrees F. I then went about whip and toungue grafting various heartnuts, Black walnuts, pecans, persimmons, peaches and mulberrys, all trees which need a warmer temp to callus. After grafting they were rubber banded and parafilm tape wrapped over the graft and all the scion. These were inserted inside the slits within the foam insulation layer covering the larger PVC pipe and wrested against the cardboard shield within. This set up was left for 21 days in the root cellar which maintained between 39 and 45 degrees over the period of days.

A couple of things to note!

  1. I feel the main difference in the two systems (mine and the one posted by Dax) are just that my system uses a 6W per foot heat tape that will get quite hot and a temp control device where Dax’s system uses a 2W per ft heat tape that is self regulating to some amount above ambient temperature. So in a cool basement or warmer place his set up is perfect! But I found if its too cold, that unknown heat tape just wont warm the union enough.
  2. I did learn from Cliff England who is an amazing wealth of info that Black walnut rootstocks will still bleed heavily even in dormant grafting!!! His solution is to place the bare root rootstocks all inside a large garbage bag with just some very slightly damp sawdust (the roots are all in the bag not the tops and its tied off) then leave them for around 2 weeks to dry out. If they bleed when cut off, they are not dry enough! I tried this and most of mine did not bleed, those which did I drilled holes in the base of the rootstock and also made knife cuts in the trunk to release sap below the graft. It seems to have worked! On a few of them that were just bleeding too much I did just do a side graft and left the top of the rootstock cut off and dripping sap, which did heal!

Those are my experiences so far, I plan on running a few hundred more trees through this winter.

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That’s a sweet setup Josh, thank you for sharing! It’s great to have alternative strategies available based on varying conditions. I think the built in static temperature control is great as long as it’s in the range you need, but knowing there is another way that isn’t much more expensive (but a bit more effort) is great. Another tool in the toolbox.

When you did this, did you heat antifreeze before capping? I don’t know if leaving less space may be useful.

No I did not. Just filled it up and glued the caps on, then after drying I wrapped and taped the heat tape on it.

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Josh, the idea behind the antifreeze being a more stable temperature control that allows the heat tape to cycle on and off less frequently, correct?

I believe so, it acts as a thermal mass holding a more constant temp than just heated air would. Water is great at holding a temperature, the antifreeze is used just so there is never a concern of freezing and busting the pipes.

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Great job! I’m intrigued by your tools - the saw and drills look like they came down to you from another generation. Very nice stuff.