Juglans regia L. (Juglandaceae) at Peter the Great Botanical Garden in Saint Petersburg

Juglans regia L. was the first exotic species of this genus to be cultivated at Peter the Great Botanical Garden of the V.L. Komarov Botanical Institute of RAS in Saint Petersburg - it was mentioned at M.M. Terekhovsky’s Catalogue in 1796. Firstly it was cultivated indoors. It was tested by E.L. Regel as early as in 1871 but unsuccessfully. It has been cultivated trustworthy outdoors since 1914. It was seriously frost damaging during the 20th century in cold winters with temperature below -25 oC, such as in 1955/56, 1968/69, 1978/79, аnd 1984/85. The winter of 1986/87 with absolute minimum temperature -34,7 oC was very unfavourable, and many trees died after it. At present, the winter hardiness has increased with the warming of the climate. There are no frost damages at all or they are small and insignificant. The largest trees now reach 19 m high and 31 cm of trunk diameter in the age of 67 years old. The majority of trees produce fruits. Twenty trees of modern collection represent the five generations. The visible increasing of adaptation abilities is observed starting with the fifth generation. The trees of the fifth generation are good looking single-trunked trees without frost damages. Since 2014 they have been producing fruits, and subsequently this is possible to obtain plants of the sixth generation. Apparently the specimens of the fifth and the next generations are of special value to test at areas outside of the city to promote the distribution of the walnut in cultivation.