Colby walnuts of 1951 crop, showing thin shells and plump, bright kernels.
The Colby tree is rather upright in growth, with strong branches, being the most vigorous among the four hardiest Carpathian seedlings at Urbana. It was one of two trees on which most catkins survived the winter of 1950-51, when temperatures at Urbana fell to -19° F. It is among the earliest Persian walnuts to start growth in spring, blossoming at Urbana normally in the first half of May. Flowering is protandrous (male flowers first) but with enough overlap of staminate and pistillate blossoms to secure a large degree of self-pollination from the abundant large catkins. Fruit set might be improved, however, by planting nearby another variety with later staminate catkins.[20] The nuts mature from the middle to the last of September and have not been seriously affected by walnut husk maggot or walnut blight at Urbana. The tree is relatively early in wood maturity, shedding its foliage usually before November, a characteristic shared by the other hardiest Carpathian seedlings in Illinois.
Prior to 1952, scions of the Colby walnut (previously designated Illinois No. 10) were propagated for test by top working on native eastern walnut (Juglans nigra) at two widely separated locations. It fruited in 1951 at Greensboro, North Carolina, where the early growth sometimes is injured by spring freezes. (This is common with Carpathian walnuts in the southeast.) It has survived three winters at Sabula, Iowa with no cold injury and made unusually vigorous growth there. At both Urbana and Sabula, it has been compared with Broadview Persian walnut, a British Columbia origination considered a hardy variety. Broadview has often suffered winter injury at both locations, and in 1950-51 was killed to the understock at Urbana.
The suggested test regions for the Colby Persian walnut include those with a climate similar to central Illinois, and where spring freezes are not generally a problem. The suggested understock is black walnut (J. nigra) though established hardy Carpathian and other Persian walnuts may be satisfactory for top working.
Additional wood for propagation of the Colby will be available in small quantities next August to nut nurserymen and other experiment stations. (Walnut scions cannot be sent from Illinois to California.) Trees of Colby should be available from several cooperating nurseries in the fall of 1953.—Reprinted from Fruit Varieties and Horticultural Digest, 6(4):72-75. 1952.