The amputation of the leading root causes the seedling to grow up instead of down and will make them start to bear nuts earlier.
In Europe instead of cutting off the walnut seedling's main roots they put under them a flat stone, or start in an earthen pot.
The next spring the walnut seedlings are ready for the permanent planting. Being permanently transplanted they should be cultivated at least two or three years.
Whitewash the walnut trunks in the late fall to protect bark from bursting by the winter sun. Put a screen around the trunks to protect them from mice and rabbits. Though, if a walnut is gnawed by rodents do nothing about it, the tree will produce a stalk—a new one—from the root.
2. Propagation by Grafting
Take Canadian black walnut seedling, one or two years old early in the spring, if you have a greenhouse and can graft them one inch above the root line, tie up with raffia, cover with melted parawax and put in boxes covering each row with light soil mixed with the moss. After 20th of May when the danger of frost is over transplant in your nursery.
The grafting of walnuts should be called a barking method. Cut off the upper part of the stock horizontally. Split the bark with your grafting knife as much as needed and lift up the bark as far as the wood and insert the scion. Tie up with raffia and do the rest as said previously.
The top grafting on the large Canadian black nuts gives good results also.
3. Budding
We bud the walnuts in the middle of August. Regular "T" cut has to be done, the bud put in and wrapped with raffia. Then it should be covered with parawax and left for a couple of weeks. After that time the budding should be examined and the raffia removed. If the leaf by the bud remains green it indicates that the grafting is successful.