Harry P. Burgart, Union City, Michigan
It is only natural that those who propagate by budding and grafting are always hoping to find a rootstock that will accept their scions with the highest percentage of takes and impart vigorous growth to the scion variety. Sometimes in our eagerness to adopt a new rootstock we are likely to neglect a vital point, namely—Future Performance of the root-top combination we are about to use.
It would take years of observation in a test planting to prove whether or not a new rootstock material is safe to use. A rootstock can affect the tree it supports in various ways. Sometimes the rootstock will force to the top too much growth, which is likely to bring about unfruitfulness. In other cases, the rootstock may cause a dwarfing habit in the future tree, with the resulting top being a scant producer of nuts. Then there is the combination where rootstock and top vary too much in their growth rate, thus making an unsightly tree. The ideal rootstock is one that attains a diameter nearly equal to the diameter of its partner, and is capable of producing a moderate amount of top growth, together with the production of heavy crops of nuts. Such a rootstock should also accept buds or grafts readily, and be compatible with the scion throughout the life of the tree.
My first experience with rootstocks for grafting came about in 1926 when I was working at the J. F. Jones Nursery then at Lancaster, Pennsylvania. Mr. Jones used both bitternut and pecan seedling stocks for grafting shagbark hickories. Pecans and hicans were also grafted on hardy northern pecan seedlings, and Japanese walnut stocks were used for butternuts and heartnuts. Black and Persian walnut scions were set on eastern black walnut seedlings.
When I returned to Michigan I brought back enough of Mr. Jones' trees for a small test planting here at Union City. These trees were planted in a heavy quack grass sod and some were lost, but those surviving show good compatibility between the top and root.
In the intervening years I have made but slight changes in the rootstock material used in my own nursery. I do not approve of the performance of our butternut varieties on the Japanese walnut root, as it results in a weak and dwarfed tree. The use of butternut rootstocks is also unsatisfactory, for they tend to produce trees of low vitality that in a few years fall victim to blight and then perish. I tried our Michigan black walnut seedlings as a rootstock and found that they are very much better rootstock material. The growth at the union is about equal. Top growth is good, and the butternut tops bear early and heavily, with no signs of blight during the ten years I have had them under test.
After years of test I have decided to use the northern pecan seedlings as rootstocks for my shagbarks, pecans, and hicans because they are a fast growing stock tree. They accept the grafts readily, and make good unions more quickly than the bitternut stocks I have tried. Mr. Wilkinson, from whom I obtain my seed, has never failed to send me seed with good viability, just about every seed germinating. The northern pecan seedlings have shown no winter injury here in Southern Michigan during the 20 years I have watched them growing.
An example of the superiority of the black walnut over the Persian walnut as a rootstock is a seedling of the variety Wiltz Mayette growing near a Broadview grafted on black walnut. Both trees are the same age, but the Broadview on black walnut is just about twice the size of its own-rooted neighbor.