Updated February, 2020. Originally posted June, 2016.
Janine Hasey, Chuck Leslie, Wesley Hackett, Pat J. Brown, Andreas Westphal, Michael McKenry, Greg Browne, & Dan Kluepfel.
Helpful terminology in understanding walnut plant material:
Cultivar (cultivated variety) – A named group of plants within a cultivated species that is distinguished by a group of characteristics, e.g. refers to a vegetatively propagated clone, such as ‘Chandler’ or ‘Howard’
Genotype – The genetic constitution of an individual.
Phenotype – An individual’s observable characteristics or traits, e.g. flower color, or nut size.
Clone – Plants (scion or rootstock) reproduced from a single plant by vegetative methods (grafting, cuttings, layering, micropropagation). Plants produced in this manner have the same genotype as the parent. Variation can exist among clones from a given plant due to their interaction with the environment.
Micropropagation– Multiplication of plants under sterile in vitro conditions in a lab followed by hardening off in a greenhouse. Most of the clonal rootstock and own-rooted walnut plant material in the trade is micropropagated.
Grafted or budded plant – A plant whose roots are of one genotype and the shoots (scion) are of a different genotype, obtained by grafting or budding a cultivar onto a rootstock.
Own-rooted (also known as self-rooted) plant – A plant whose roots are of the same genotype as the shoots. It is obtained by micropropagation or rooting stem cuttings.
Seedling – A plant propagated from seed.
Plantlet – A plant propagated by vegetative methods e.g. micropropagation.
Liner – A young rooted plant used for transplanting into a nursery row or larger container.
A walnut plant can be purchased as a:
- Rootstock – A seedling or clonally produced tree, to be subsequently field grafted or budded to the desired English variety (cultivar). Before 2007, most rootstocks have been seedlings: Seedling black, seedling Paradox hybrid (black x English), seedling English (no longer available). Clonal Paradox rootstocks with selected characteristics are now favored by many growers and are available from many nurseries. They are sold as potted plants or bare root trees.
- Two-year old tree – A two-year nursery finished tree product where growth of the rootstock is started in the first year and growth of the English variety scion is completed in the second year. The scion is added either by budding the rootstock in the fall of year one or by grafting the rootstock in the spring of year two.
- June-budded tree – A one-year old finished tree with the English variety budded onto the rootstock at the nursery in the spring or early summer. The nursery tree will typically be smaller than a two-year tree, however, research and experience have shown that the grower’s orchard tree at the end of the first growing season can be as large as or larger than a two-year tree.
- Own-rooted (also known as self-rooted) tree – An English variety rooted and grown on its own roots until ready for orchard planting. There is no graft or bud union.
Availability in nursery trade:
- Rootstocks (sold as ungrafted or unbudded trees): Seedling Paradox, seedling black, or clonal Paradox ‘VX211’, ‘RX1’, or ‘Vlach’ (and possibly other clonal rootstocks).
- Clonal rootstocks are sold as potted (container) plants or bare root trees.
- Nursery grafted or budded trees: Various English varieties on seedling Paradox, seedling black, or clonal Paradox ‘VX211’, ‘RX1’, or ‘Vlach’ (and possibly other clonal rootstocks) sold as bare root trees.
- Potted Finished Trees (clonal Paradox rootstock): Grafted walnut tree in pot (container); limited and sporadic availability. More research needed on field performance – ongoing.
- Own-rooted English trees: Sold as bare root or potted trees. Available by custom order (at least one year advance notice required).