Hot Callus Grafting

We use this method in the winter months to graft many different varieties of Japanese maples, pines, and fir. It involves heating the immediate area around the graft union to about 70 degrees for a period of 2- 3 weeks, or until the graft union shows signs of callusing. The apparatus is called a "hot callus tube".

Our method of construction is as follows:

1- thermostat with remote capillary sensor
1- 20' roof heating cable assembly
1- ten foot section of 2" schedule 80 PVC
1- 2" PVC coupler
1- 1"x4"x10' board
1- 10' half inch copper tube
1- half inch copper end cap
1- half inch elbow with a female threaded adapter on one end (this enables the copper to be filled with light oil and sealed.)
1 roll of sill plate gasket
12"x 10' strip of poly sheeting

Start by cutting the 10' length of PVC into two 5' sections and secure them together onto a suitable board. This makes the task much easier. Cut ½" slots in the PVC tube every 1 1/2" inches on center. We used a radial arm saw to cross cut and a roto-zip® to pop out the slots and clean out the opening of any rough edges. EXERCISE EXTREME CAUTION IF USING THE ROTO-ZIP®.
Adhere sill plate gasket to the 10' board. Attach the coupled PVC tube ,using screws, with slots facing up to the gasket side of the board.
Cap one end of the copper tube and install the elbow with threaded female adapter on the other end. Round out one end of the PVC to fit the threaded end of the copper tube.
Fill the copper tube with a light oil of your choice leaving room for expansion. Cap the female end. Using a quality electrical tape, secure the heating cable along each side of the copper tube.
Insert the copper tube with the heating cable attached into the PVC Try to keep the heat cables at the lowest part of the PVC tube. Staple sill plate gasket along each side of the PVC Adhere the gasket together forming a seam. Next, cover the entire hot callus tube with poly sheeting. Feel out the slits in the PVC and carefully slice into them with a utility knife. DO NOT SLICE THE HEATING CABLE!!!
Place the hot callus unit into a desired location and set up the thermostat. Locate the center most slots and insert the capillary end. Keep the capillary at the highest part of the tube, up off the copper and heating cables. Secure with zip ties.


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