With some difficult to graft species, a warm temperature around the graft can be beneficial.
The hot-pipe callusing system warms the graft union to about 80°F. but keeps the roots and buds on the scion cool (about 45°F.) to prevent their premature growth.
Species that benefit from this technique include various fruit crops and ornamentals like maple (Acer), hazel (Corylus) and beech (Fagus).
The graft union is kept warm by a PVC or copper pipe that contains a hot wire or recirculating hot water system.
The entire system is insulated around the graft and the scion and roots are kept cool. As in all grafts, the union must be kept from drying out.
Hot-pipe callusing is performed in the late winter or early spring.