When seedlings of nut trees and other tap-rooted species are transplanted from nursery to orchard, the percentage of survival in often quite low. Perhaps the chief reason for this failure is the marked and pronounced tendency of most tap-rooted plants to produce little or no fibrous, branched roots in lieu of the long, straight, and seldom branched tap roots.
The common practice of undercutting seedlings during the dormant season to induce a branched root system requires additional labor, and often results in reduced growth and vigor during the following season. The use of hardware cloth or other close-meshed wire is effective, but this method also has the disadvantage of being relatively expensive for the nurseryman.
Preliminary work carried on during the past two years has shown that with certain nut trees and other tap-rooted plants, it is possible to induce fibrous roots by growing such seedlings in vermiculite. The methods and results of this work are presented in this paper.
Material and Methods
Seeds of black walnut (Juglans nigra), Persian walnut (Juglans regia), Chinese chestnut (Castanea mollissima), pignut hickory (Carya glabra), shellbark hickory (Carya laciniosa), shagbark hickory (Carya ovata), pecan (Carya illin), pawpaw (Asimina triloba), and three persimmons (Diospyros kaki, D. lotus, and D. virginiana) were stratified in moist sawdust for three months at a temperature range of 35 to 40 degrees F. After this period of stratification the seeds of each species were divided into three lots and planted in flats 25 x 26 x 6 inches containing one of the following media: (1) sharp sand of the type used in potting soil, (2) potting soil, and (3) vermiculite. Seeds were kept moist with ordinary tap water and allowed to germinate and grow in the greenhouse. When the seedlings had grown two or three true leaves, they were carefully removed from the medium and examined for the type of root system developed.
Results
In the first eight species listed in Table 1, the differences between branched and tap-rooted seedlings were quite pronounced. The few tap-rooted seedlings growing in vermiculite medium showed some laterals and were less strongly tap-rooted than those in soil or sand. Pawpaws in soil and sand media were practically devoid of laterals, and their fibrous root system in vermiculite was not as pronounced as with the walnuts, hickories, and pecans. Of the species studied, the persimmons
Table 1.
Sand Soil Vermiculite
Species Number of plants
Tap rooted Fibrous Tap Fibrous Tap Fibrous