Since I live and grow fruit trees in Minnesota, most of my research have been with cold hardy rootstock and interstems. My goal has been to produce a salable, lightly feathered 2 year old whip. Our short growing season doesn’t allow for us to use the west coast procedures.
Our machine for making the mortise and tenon graft was the first break through. We are now able to graft very large scions to produce a 2 year old whip.
This will be our third year of research as to what works best for us. I start with 3/8 inch Bud 118 rootstock and bench graft a 12 inch Bud 9 interstem to this. Since the first graft is going to be buried, I graft as low as I can on the rootstock. This is usually about 4 to 6 inches up from the new roots. The new grafts are stored in an area maintained at 45 ˚F. In late April these new grafts are potted up into 1 gallon containers and set out in our container area under overhead irrigation. These 1 gallon plants are the foundation of the next procedure. In November we will move the plants into a cold frost free area to be ready for grafting the scion in December.
Penn St. University suggests to bury the graft on the interstem by 1 inch. Since many of the growing ranges in Minnesota have poor soil drainage my recommendation would be to plant the interstem graft level to the existing soil and cover with mulch to 4 inches. Eventually the interstem would root into the mulch giving the desired effect of planting below grade.
Our machine graft allows us to graft on a 3 to 5 Ft. scion. After tying in the scion, it is staked using a 4 Ft. by 3/8 bamboo stake. This stake allows us to straighten the scion and prevents the scion from moving. The new grafts are set into a 45 ˚F greenhouse to callus. In March we are going to cover the scions with a narrow plastic bag to make the buds break without cutting back he leader. Most books suggest to cut back the leader but this procedure is not necessary if the buds break and develop a nice lightly feathered whip. After the buds break I’m going to remove the plastic bag and spray the new growth with Promalin to stimulate new growth.
By June of 2012 we should have a good idea of how bagging and spraying with Promalin really works.
So far this has been the extent of our research in producing a 2 year old whip for early summer sales in 1 gallon containers. We are open to new suggestions.